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Filters FAQ and Links pages

Center filters can cost an amazing $2,850 US$ (for Super Angulon 210mm f/8). So many of us have an interest in possible solutions we can do for less. In some cases, center filter use may be optional, depending on your choice of subject and technique. Modern digital filtering and image merging (multiple exposures at different stops on tripod..) may make it possible to achieve more uniform effects with less effort. Finally, some photographers have had success with making their own low cost center filters, with their tips available to you below.

Related Postings

Date: Tue, 11 Jan 2000
From: "Alexander Kraus" [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Making a center filter...

Todd E. Maurer [email protected] wrote

> When researching the Metrogon that Mr. Grimes' WEB put me onto, I got to
> see pictures of that lens' center filters.  These seemed to simply have
> an asterisk pattern of metal foil in the center.  I couldn't tell if the
> foil was opaque or semitransparent.
>
> Anyone ever try making their own center filter by just putting an foil
> asterisk on a clear filter?  Seems like too simple a solution...  Not
> near as elegant as a neutral density filter that gradually gets darker
> in the center.  But it seemd like it might actually work. I'd expect it
> to be sensitive to the aperture setting. But hey for the cost difference
> between a UV and a "real" center filter, I could make a filter (even
> from multi coated glass filters  for every marked aperture and still
> save a bundle.
>
> Todd     

Well, I'd bet this would really diminish the performance of the lens. First of all you would need a foil that is

a) perfectly neutral grey,

b) perfectly planparallel (equally thick everywhere) and

c) optically homogeneous.

Secondly you need to glue it to the glass. Again you need a perfect crystall clear glue and you have to apply it equally thick everywhere to avoid bumps. After all you don't want to copy a Zeiss Softar ;-) The foil has to be semitransparent. Since the depth of field of a wide angle lens is very large, an opaque foil would cause a black spot in the center of your image. I think these prerequisites cannot be fulfilled without very sophisticated equipments/materials.

You might try an other approach. Take a (cheap) UV-Filter, cut a star-shaped mask out of cardboard and place it a couple of millimeters above the glass surface. Then spray a *very fine* mist of flat black paint through the mask towards the glass. Let the distance between can and glass be at least 2 feet in order to avoid getting an completely opaque black spot.

I have never tried this procedure my self and I have never heard that another one did it before, but I think it might actually work.

If it fails - just clean the filter with some methylene chloride or acetone and you haven't lost anything. If you try it, don't forget to post how it works! :-)

Alex

From: Bill Peters [email protected]
Date: Thu, 13 Jan 2000
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Making a center filter...

Todd,

Metrogon Centre Filters are available from the Surplus Shed in red and yellow for a few dollars each. These are the evaporated metal type. The ones I got had some minor surface damage and fungus spots - more cosmetic than anything that would degrade performance. They are so inexpensive you might order two or three and cherry pick.

Now if you want to shoot color :-\

http://www.surplusshed.com/filters.html

cheers,
Bill Peters

Date: Fri, 14 Jan 2000
From: Harald Finster [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Center Filter? who uses, comments please

Hi Rodney, hi all,

[email protected] wrote:

> I've seen them for sale for extreme wide angle lenses.  I am curious
> if they are necessary?

The answer depends on your application.

You WILL need a center filter, if you are going to photograph evenly illumuinated objects. If you are working on B&W, you can compensate the light falloff in your darkroom - that's the poor man's solution :-)

In same cases, e.g. in landscape photography, the light falloff might even be useful. If you shift your lens up, the falloff 'replaces' the graduated neutral density filter.

> I have a 90mm Nikkor f8 and I guess it doesn't need a filter, because
> I have noticed no light fall-off in my transparencies. 

I had some experience with a 47mm lens, which definately REQUIRED the filter. But a 90mm might be ok without one.

Harald

Date: Thu, 13 Jan 2000
From: "M. Denis Hill" [email protected]
To: [email protected]
Subject: RE: Fuji G617 focusing screens, ND filter usage, etc., questions

In my experience, the center filter becomes optional when:

a) The subject does not contain large areas of even tones extending into the corners (e.g., sky), or

b) The lens is stopped down to f22 or beyond, or

c) A combination of "a" and "b."

I've heard one prominent IAPP member claim that she never uses a center filter on a Fuji, just stops way down.

IMO, it is preferable to get the image as right as possible in the camera.

BTW, stacking a standard filter behind the center filter (in my case, a Heliopan) caused severe vignetting at nominal apertures.

The correct way to frame an image with the G617 is to line things up so you see the level in the notch at the bottom of the viewfinder frame. In my experience, I often found this gave accurate framing on the vertical axis, but I usually got extra image on the horizontal axis. Although I never used one with the G617 I owned, I think a ground glass would be a very useful accessory unless you want to frame with fudge factor.

As I recall, using a cable release on the lens did not tell the winding mechanism an exposure had been made.

The Fuji is a real workhorse. Enjoy it! And don't forget that it takes vertical pictures, too.

M. Denis Hill
Area 360 Communications
http://www.area360.com

Date: Tue, 11 Jan 2000
From: "Alexander Kraus" [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Making a center filter...

Todd E. Maurer [email protected] wrote

> When researching the Metrogon that Mr. Grimes' WEB put me onto, I got to
> see pictures of that lens' center filters.  These seemed to simply have
> an asterisk pattern of metal foil in the center.  I couldn't tell if the
> foil was opaque or semitransparent.
>
> Anyone ever try making their own center filter by just putting an foil
> asterisk on a clear filter?  Seems like too simple a solution...  Not
> near as elegant as a neutral density filter that gradually gets darker
> in the center.  But it seemd like it might actually work. I'd expect it
> to be sensitive to the aperture setting. But hey for the cost difference
> between a UV and a "real" center filter, I could make a filter (even
> from multi coated glass filters  for every marked aperture and still
> save a bundle.
>
> Todd

Well, I'd bet this would really diminish the performance of the lens. First of all you would need a foil that is

a) perfectly neutral grey,
b) perfectly planparallel (equally thick everywhere) and
c) optically homogeneous.

Secondly you need to glue it to the glass. Again you need a perfect crystall clear glue and you have to apply it equally thick everywhere to avoid bumps. After all you don't want to copy a Zeiss Softar ;-) The foil has to be semitransparent. Since the depth of field of a wide angle lens is very large, an opaque foil would cause a black spot in the center of your image. I think these prerequisites cannot be fulfilled without very sophisticated equipments/materials.

You might try an other approach. Take a (cheap) UV-Filter, cut a star-shaped mask out of cardboard and place it a couple of millimeters above the glass surface. Then spray a *very fine* mist of flat black paint through the mask towards the glass. Let the distance between can and glass be at least 2 feet in order to avoid getting an completely opaque black spot. I have never tried this procedure my self and I have never heard that anothe r one did it before, but I think it might actually work. If it fails - just clean the filter with some methylene chloride or acetone and you haven't lost anything.

If you try it, don't forget to post how it works! :-)

Alex

Date: Tue, 11 Jan 2000
From: "Todd E. Maurer" [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Making a center filter...

When researching the Metrogon that Mr. Grimes' WEB put me onto, I got to see pictures of that lens' center filters. These seemed to simply have an asterisk pattern of metal foil in the center. I couldn't tell if the foil was opaque or semitransparent.

Anyone ever try making their own center filter by just putting an foil asterisk on a clear filter? Seems like too simple a solution... Not near as elegant as a neutral density filter that gradually gets darker in the center. But it seemd like it might actually work. I'd expect it to be sensitive to the aperture setting. But hey for the cost difference between a UV and a "real" center filter, I could make a filter (even from multi coated glass filters for every marked aperture and still save a bundle.

Todd

From Panoramic Mailing List:
Date: Sun, 19 Dec 1999
From: Joel Seaman [email protected]
Subject: Re: Horseman 612

John,

Some folks allegedly are successful with the 45MM. They seem to get by with the help of a Schnieder Center filter which is a 2 stop (4X) filter, and substantially less expensive. I did have occasional images that worked well with the 45MM, but this was extremely inconsistent. Rodenstock recommeds a 1 1/2 stop for both lenses. The Rodenstock 1 1/2 stop (ND 0.45) is the same as the Heliopan which you might find for less money. I have the ND 0.45 Rodenstock but since they are "hand made" they vary in actual compensation, and therefore my 1 2/3 stop Velvia / 100VS solution. You will have to test yours to see what it really needs. Rodenstock told me that the ND 0.45 should require only 1 1/3 stop compensation.....fat chance.

When I bought my Horseman Samy's Camera had the best price which was their 612 kits, although, other then giving Samy's my credit card # and receiving the camera, I found them to be less than useless and less than helpful.

Good luck

Joel

From: "Todd E. Maurer" [email protected]
Newsgroups: rec.photo.equipment.large-format
Date: Thu, 27 Jul 2000
Subject: Re: f/8 vs. f/5.6 65mm Super Angulon

The center filter might help even things out. I just got mine for my 65 mm F8. Haven't have time for even a test shot! The less expensive Heliopan was hard to come by as they are discontinued. Around $200+-20 if you can find it in stock. The Schneider one is available but a special order item. I was quoted $310 to $500 depending on the dealer.

I won't count on much if any movement. The previous owner had this lens mounted off center on its board for shooting architecture with roll film. I found I had to drop the standard to prevent the worse of the vingetting.

BTW Schneider's web site does not recommend this lens for 4x5.

Todd

Alan & Juliet Duncanson wrote:

> I am looking for a 65 mm lens to use with 6x9
> and 4x5 formats.  I am attracted to the f/8
> Super Angulon in part because of the low price
> for which they are sometimes available.
>
> It appears that, at 100 deg. coverage, the f/8
> will just barely cover 4x5 with no movements.
> Will a center filter help, and maybe allow it
> to cover 2 cm of shift?
>
> Does the f/8 suffer in terms of sharpness in
> comparison? I will be making about 5x
> enlargements.
>
> Thanks - Alan

From Panoramic Mailing List:
Date: Wed, 02 Aug 2000
From: Michel Dusariez [email protected]
To: [email protected]
Subject: Graduated Filters

Dear panoramist,

I remember to all of you that I am a retail optician in Brussels, Belgium.

About graduated filters, you have to know that it's very easy to made some yourself.

In any rx spectacles glass factory, who made glass (mineral and organic - plastic ) for retail opticians, they made any coloration on organic eyeglass, they put the plastic glass in some tinting liquid at 90-95 centigrade temperature for a few minutes.

The tinting powder come in different hues as well neutral gray and is very inexpensive, you can color a lot of glass in one liter of liquid.

The coloration is darker as the glass stay more in the liquid.

They made easily graduate by immersing more or less some part of the plastic sheet.

With some training it is maybe possible to made some central dark spot.

I hope to have give all off you some usefull informations.

Michel DUSARIEZ.

PS : The last edition of the book " 360� PANOPTIC PHOTOGRAPHY EXPERIMENTS" is nearly all sold, last copies are always available, persons interrested can ask more info by E-mail.

>Ya, sure, Peter, I use graduated filters on that thing a lot.  And boy, oh
>boy, they have really made a difference; several photos in my new book
>involved the Fuji 617 with 2 or 3 stop ND graduated filters.  I use the
>Tiffen Glass ones; they cost about $125 each a few years ago.  They're
>rectangular, so one can slide them up and down without getting the edge of
>the filter in the frame.  This does limit their use when doing verticals,
>though, because the filter only barely fits inside the "roll bar" and so the
>horizon of dark and light is stuck in the center then.  But hey, it works.
>Some of those verticals need a little cropping anyway.  The nice thing about
>glass is that it's a lot harder to scratch than resin is.  Also, these are a
>nice neutral gray compared to some of the green or amber "grey" that I've
>seen on the market.
>
>Liz Hymans
>
>In a message dated 8/1/00 6:38:13 AM Pacific Daylight Time,
>[email protected] writes:
>
> I find the need for graduated filters for the Fuji GX 617. 

Michel DUSARIEZ
UNLIMITED FIELDS RESEARCH PANOPTIC IMAGING
KITE AERIAL PHOTOGRAPHY WORDWIDE ASSOCIATION - FOUNDATION
14, Avenue Capitaine PIRET
B-1150 BRUXELLES - BELGIUM
Fax 32 2 512 68 29      

From Panoramic Mailing List:
Date: Sun, 20 Aug 2000
From: "[email protected]" [email protected]
Subject: Re: Linhof 6x17 filter question

as the manufacurer of 612 shift cameras i have found the centerfilters very a great deal no matter what the annouonced factor is. Probably 3x (1 1/2 stops) is a good starting point. if you are shooting transparencies you do not want to overexpose of course, on contrary with color negs i expose for the far corners if i want an even result which i get by printing in the center w/o image damage. to deterning the filter factor I take a good spot meter 1 degree best, read the center and then the clear edge holding filter in same position with a light wall as background.ralph

> From: Denton Taylor [email protected]
> Reply-To: [email protected]
> Date: Sat, 19 Aug 2000 
> To: [email protected]
>
> Hi all...
>
> I'm the very fortunate owner of a Technorama 6x17 with fixed 90 SA...
>
> I also got the graduated center filter, which, after a roll of chromes
> without it, has made it clear that I need it all the time :-)
>
> But, does anyone know what the filter factor is? Bracketing 6x17 gets
> expensive :-)

Date: Fri, 13 Oct 2000
From: C. Downs
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Centering Filters: Required When?

Paul Mozell [email protected] wrote:

>These babies are expensive. Which focal lengths make the best use of
>them? Please tell me I won't need one for 75mm!

For many applications you might be able to avoid using one for 75mm on 4x5 film.

I believe that David Muench leaves the filter off for most shots. He is probably the best known photographer that specializes in this particular lens. His main film for color is Velvia so it's possible to not use it even with contrasty films.

My favorite lens for 4x5 wide angle is the 58XL and unless I'm shooting something that has to be even from edge to edge like a blank wall used for commercial advertizing the center filter is not used. This applies mainly to nature images and will not apply for some types of commercial work where the background is to be exactly the same from corner to corner but for most other work even commercial no filter is needed for the 75mm. Actually the light fall off for nature work works very well to give a slight darkening at the corners that many achieve by burning and dodging.

You might want to check out one of the many books that David Muench has out and see if the slight darkening doesn't seem to work well. In B&W if you are aware of the slight light loss at the edges you can increase the exposure just a bit and dodge the center when printing. Again the effect is not that distracting and sometimes works really well. DO be careful if you use a polarizing filter with the wide angles as they will sometimes give very uneven skies. This happens due to the angle of light coming from one side of the sky is partly polarized and on the other end of the image the angle is too far off of the polarizing axis to work as well.

I certainly would try the lens for a while without the center filter and see if you can live without it. It is a pain to use as it is easily scratched and as you said expensive to replace. It adds another couple of surfaces to flair and you do loose light. One of the strange things I have noticed is that the same formula lens on an 8x10 camera { around 150mm} is not usually questioned as to the need for the center filter and the light fall off is the same. If you have access to any of the books in the "Images of Wildness" series look for George Humphries work and you will see the majority of images are shot on 4x5 with the 75mm.....never a center filter used.!

As I said try it with out the filter and for most things I think you will be happy.

Date: Fri, 13 Oct 2000
From: [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Centering Filters: Required When?

[email protected] wrote:

> These babies are expensive. Which focal lengths make the best use of
> them? Please tell me I won't need one for 75mm!

Whether you feel you need one or not has to do with your taste and how you use the lens. If you want a quantative answer and you are using a schneider 75 SA, you might go to their website (http://www.schneideroptics.com/large/super_angulon/75/daten.html) will get you directly to the description of the 75 SA. There is an illumination curve that tells you the percent illumination as a function of the distance off axis. You can convert % to f:stops (50% means you need 1 more f:stop). If you want the answer from Rodenstock you can probably find it in their brochures. If you want it from Nikon, or Fuji, well you're out of luck, but their lenses should be similar to Schneider and the illumination fall-off seems to me a little less. Thus, the Schneider curves are probably a good guide.

If you are troubled by the cost, sometimes a used one is available a little cheaper. There are both Heliopan and OEM versions. Personally, I think they are both very good.

Good luck.

From Contax Mailing List:
Date: Thu, 16 Nov 2000
From: Bob Shell [email protected]
Subject: Re: AW: [CONTAX] Re: Ziess Jena

Also, there were some wide angle lenses which had little propellers (like on an airplane) on the front. You would spin the propeller just before taking the photo, and this worked like a graduated neutral density filter to even out the illumination.

Bob

[Ed. note: handy note, as I have suspected this, but glad to see it confirmed by an owner/user...]
Date: Mon, 15 Jan 2001
From: [email protected]
To: [email protected]
Subject: Crazy prices

I was forced to purchase a graduated center filter for my Hasselblad Xpan's 45mm lens at a price of $240. Despite what Hassleblad says, the severe light drop-off in this lens prevents successful use even with print film with most subjects. This filter should be provided with the lens or camera kit, but is not. The price is about half of what you pay for the whole lens. Conversely, I paid less than that for a huge (and beautifully made) center filter for my LF Schnieder 75mm Super Angulon.

Date: Sat, 13 Jan 2001
From: [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: How Could You Build A Practical Center Spot Filter?

I've got a couple of older WA lenses with excellent coverage... I'm also trying to pick up one or two of the modern WA lenses with incredibly excellent coverage. But the center spot filters are not available for the classics and are EXPENSIVE for the new lenses.

A couple of friends and I talked about making our own. The problems are serious (which is partly why they are expensive), but workable. Anyone got ideas how to do it? Here are some random thoughts...

1. Color neutral materials are a challenge. Litho film is pretty good, as is copier toner suspended in gel.

2. You can compute the function on a computer and plot it, but it needs to be calibrated for each lens.

3. The center spots for modern lenses are not the pure cosine to the forth function, because the lens geometry is so complicated.

4. One approach would be to photograph a white field through the lens, and then mount the resulting negative as a filter to produce a uniformly bright image (the lens would be the definition of its own filter).

5. Another approach would be to calculate the filter and then print it out using photoshop onto transparency material.

Any contributors or aiders and abbetters out there?

Date: Sat, 13 Jan 2001
From: Michael Briggs [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: How Could You Build A Practical Center Spot Filter?

[email protected] wrote:

cut...

> But the center spot filters are not
> available for the classics and are EXPENSIVE for the new lenses.

I don't think that you need have a center filter designed by the lens manufacturer for excellent results. Heliopan markets a line of "generic" center filters at somewhat lower cost than those of the lens manufacturers. A Heliopan (or Rodenstock or Schneider) filter of the right diameter would probably do a good job on a classic lens. AFAIK, neither Fuji nor Nikon produce center filters for their lenses, so users who want a center filter will have to buy one made by a different company.

> A couple of friends and I talked about making our own.  The problems
> are serious (which is partly why they are expensive), but workable.
> Anyone got ideas how to do it?  Here are some random thoughts... cut...
> 5.  Another approach would be to calculate the filter and then print it
> out using photoshop onto transparency material.

I think your last idea is the best, because it is cheap and plenty good enough. I don't think you need to do any calculations. Just set up some radial gradients and print out to transparency material, then take test photographs and select the one you like. If your ad hoc center filter gives good results, then its good for the job. For testing, I suggest focusing the lens on a distant object, then pointing the camera at a nearby evenly illuminated, single-toned object, perhaps a piece of postboard in sunlight. Your testing will reveal evenness of illumination and how much exposure compensation is needed.

I am not sure that the manufacturer's base their center filters on mathematical calculations. They do NOT aim to produce completely even illumination of the negative. If they did, the required exposure compensation would be too high for convenient use. Perfectly even illumination of the film isn't required: few scenes are evenly luminous and the printing process can compensate for some unevenness.

--Michael

Date: Sun, 14 Jan 2001
From: Tadeuz Jalocha [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: How Could You Build A Practical Center Spot Filter?

You could use sheets of Colour-diapositive material. Expose thru the lens with cyan light and you get a yellow Center filter if you develop in C-41. For B/W much better than a grey one.

The first center-filter i know of was made by rodenstock and was yellow too.

...

Date: Tue, 16 Jan 2001
From: [email protected] (Sandy King)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: How Could You Build A Practical Center Spot Filter?

[email protected] wrote:

> I've got a couple of older WA lenses with excellent coverage...
> I'm also trying to pick up one or two of the modern WA lenses with
> incredibly excellent coverage.  But the center spot filters are not
> available for the classics and are EXPENSIVE for the new lenses.

I have followed this thread (including the links) and found some interesting ideas that might be worth a try for my needs. I would certaily be interested in being kept informed of any follow-up information that may become available. My situation is that I have a very large lens, a 210/f/8 Super Angulon which I use with my 7X17 and 12X20 cameras. At this coverage fall-off in illumination is quite severe. Since I do a lot of work with this lens I would be happy to buy a center filter for a moderate price. Unfortunatley, the only thing available for this lens (which has a 136mm screw-in thread) is a sporadically available center filter that would set me back $2850.00 list). Yes, that is right, no transposition of zeroes as I first thought when quoted the price.

Thanks to those who are interested in the topic to keep me informed of any off-list developments about buiilding one of these center field beasts.

Sandy King

Date: Tue, 16 Jan 2001
From: "Nicholas O. Lindan" [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: How Could You Build A Practical Center Spot Filter?

[email protected] wrote:

> I've got a couple of older WA lenses with excellent coverage...
> I'm also trying to pick up one or two of the modern WA lenses with
> incredibly excellent coverage.  But the center spot filters are not
> available for the classics and are EXPENSIVE for the new lenses.

You could make a mechanical center filter that spins.

There is an old extreme WA lens that did this trick (heliogon?). The center filter was a fan that sat in front of the lens and was powered by the photographer's breath.

A clear filter with the right ratio of dark to light painted on it, mounted in a polarizing filter holder and spun by a small DC motor might do the trick.

--
Nicholas O. Lindan, Cleveland, Ohio [email protected]

From Leica Topica Mailing List:
Date: Sat, 20 Jan 2001
From: "Henning J. Wulff" [email protected]
Subject: RE: [Leica] my first test with the 12/5.6

Dan Cardish wrote:

>I've thought of that, and in fact I think Voigtlander sells a bubble level
>thingy to attach to the hot shoe.  Problem is, to make sense of this I
>think you would have to use a tripod, and I generally don't use one.
>
>dan .c
>
>At 04:38 PM 20-01-01 -0800, Frank Filippone wrote:
>>You might want to consider a bubble level?  It would help with the
>>horizon.... I use a Craftsman bubble level just laid on top of my
>>hood.....this does require a tripod and a flat spot on the hood!  Cost is
>>about $4.
>>
>>Frank Filippone
>>[email protected]

Dan, I have the bubble level and double shoe and they work well, although only in horizontals. I use this handheld. If I use a tripod I use a better level; an electronic one I carry with me on all architectural shoots.

Another solution is one of the little shoe mounted levels and the Voigtl�nder double shoe. You can't see the bubbles as well from the shooting position with your eye to the finder, but they work in both horizontal and vertical orientations.

Usually I find the light falloff unobjectionable, but if I want to even it out Voigtl�nder makes a filter adapter that takes 77mm filters, and Heliopan makes a relatively reasonable center filter. If you have other center filters, any of the larger ones from 82mm on up can be adapted and won't vignette.

Watch out for some center filters that have a sharp transition from the grey to the completely clear; this doesn't matter for the 72mm and longer focal lengths they were designed for, but the dof of the 12mm is such that this transition can be visible. I have an older filter for the 90/5.6SA that's fine, but a newer one for the 72/5.6SA-XL is not. It's the same problem that the 15 Hologon filter had and caused a visible line in even toned (sky) areas.

--

    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:[email protected]
  |[ ]|     http://www.archiphoto.com

From: "Larry Whatley" [email protected]
Newsgroups: rec.photo.equipment.large-format
Date: Wed, 17 Jan 2001
Subject: Re: How Could You Build A Practical Center Spot Filter?

If you're willing to give up some exposure range on the negative (FP4?) you could just expose for the edges and use a negative center filter in printing, the advantage being that the filter wouldn't have to be a particularly good one. But I guess that's just another way of dodging... that being what you're trying to avoid.

- Larry Whatley

Sandy King [email protected] wrote

> > I've got a couple of older WA lenses with excellent coverage...
> > I'm also trying to pick up one or two of the modern WA lenses with
> > incredibly excellent coverage.  But the center spot filters are not
> > available for the classics and are EXPENSIVE for the new lenses.
> >
>
> I have followed this thread (including the links) and found some
> interesting ideas that might be worth a try for my needs. I would certainly
> be interested in being kept informed of any follow-up information that may
> become available. My situation is that I have a very large lens, a 210/f/8
> Super Angulon which I use with my 7X17 and 12X20 cameras. At this coverage
> fall-off in illumination is quite severe. Since I do a lot of work with
> this lens I would be happy to buy a center filter for a moderate price.
> Unfortunatley, the only thing available for this lens (which has a 136mm
> screw-in thread) is a sporadically available center filter that would set
> me back $2850.00 list). Yes, that is right, no transposition of zeroes as I
> first thought when quoted the price.
>
> Thanks to those who are interested in the topic to keep me informed of any
> off-list developments about buiilding one of these center field beasts.
>
> Sandy King

rec.photo.equipment.medium-format
From: [email protected] (Heavysteam)
Date: Sat Apr 14 2001
[1] Re: Hasselblad Xpan vs 645

I haven't tried it yet, but I'm told that you won't experience fall-off if you stop it down to f16 or f22. Has anyone tested this?

I still had fall off at f16. Don't forget that this end of the aperture reduces sharpness because of diffraction and the lens seems to hit maxium sharpness right around f8. The only solution I could come up with is to bite the bullet and get the center filter. Now I have no problem using the 45mm lens in it's maximum sharpess range. One big bonus that has already paid for the center filter architectural exteriors. It's ideally suited to long low buildings, and I find that I can get a very acceptible shot with just the Xpan and a tripod instead of hauling out the 4X5. This saves a lot of time and allows me to bring the image into the computer with a scanner at the office instead of drum scanning a 4X5.

From rangefinder mailing list:
Date: Wed, 29 Aug 2001 
From: [email protected]
Subject: xpan true PANORAMA center filter q.


Ok,

after shooting with my xpan true panorama camera :) for a while I find that
it's all I ever wanted. Their 45mm lens takes care of 95% of my needs and 30mm
that I bought just sits in the box because camera becomes little too big with
an extra finder mounted on top. But I took it for couple of climbing trips and
some deep sea fishing and camera did great.  But...

I know that center filters exist for a reason. Since one came included with a
30mm I was thinking about picking one up for my 45mm. At the same time I'm
under assumption that you only need to use center filters when you shoot wide
open. If you shoot around f/8 fall off/darkening on the corners/vi^$@#! (damn
kinky word) is not as great (again my assumption). Also according to manual
there is a 1.5 EV lost in light when one uses center filters. Wouldn't 
that create a real problems when shooting landscapes at dusk or dawn. Wouldn't that
destroy all shadows? I hate loosing light becasue of filters, hass/fuji lenses
are slow enough already. I also hate the fact that I have to put a $250 piece
of glass on and off the lens which makes me feel uncomfortable. Is there any
general rule for using center filters? Should I just leave it on all the time?

Matt

ps.
Word of advice: don't fish and shoot at the same time. Your camera will smell
like fish market and all the cats in the area will become your best friends
regardless if you own a dog or not :).

Matt





Date: Sat, 16 Feb 2002 
From: Michel Dusariez [email protected]
To: [email protected]
Subject: Re: Center filter for XPAN

Hi,

I have always consider that grey center filters are required to
compensate a lack off coverage (quality) of some optics or from basic
bad construction.

If an optic is well constructed the front and rear lenses will be big
enough to give same lighting on all surface of the film as well as
the edges.

If not, the optic is not constructed to such film size. I am surprise
that such well-known brands propose such optic with lack of coverage.
In addition the center grey filter will reduce the usable opening
diaphragm.

As everybody knows an optic must fully cover a circle of size of the
diagonal of your film size.

Michel DUSARIEZ
Optician



>Marty,  Center filters are used with any lens that covers a wide viewing
>angle to compensate for the falloff of light from the center to the corners
>of the image, which is not a defect in the lens design but a limitation of
>physics.  A center filter is dark gray at the center & changing gradually in
>a radial direction to clear at the edge.  The wider the angle of view of the
>lens, the darker the center is.  A center filter is typically matched by the
>manufacturer to a particular lens that it will be used with since in general
>light falloff varies with each lens.  Thus, I would definitely get the one
>that Hasselblad makes for the Xpan 45mm lens.  It has 49mm threads & the
>hood for the 45mm Xpan lens will mount on the 45mm with the center filter in
>place.  It's Hasselblad part #54453 & you can read a description of it at
>this URL:
>
>http://www.hasselblad.com/products/cameras/xpan45.html
>
>The only drawback is that is has a list price of $234.  However, bargaining
>with a dealer who wants to make a sale should help a bit.  I'm not positive
>what the etiquette on this list is regarding recommending particular dealers
>but if you contact me offline I can suggest a good one with reasonable
>prices.
>
>Regards, Ted
"[email protected]"  wrote:
>
>>  Dirk, Kerry & Ted --
>>
>>  Thanks for your comments, they are very helpful.  I'm not familiar with
>>  center filters.  Is there a particular brand/model that you use or
>>recommend?
>>
>>  Marty

--
http://www.pano360.org/
Michel DUSARIEZ
UNLIMITED FIELDS RESEARCH PANOPTIC IMAGING asbl




Date: Sat, 16 Feb 2002 
From: ralph fuerbringer [email protected]
To: [email protected]
Subject: Re: Center filter for XPAN

The foremost optical designer of the 20th century was L. Bertele, at 19 the
designer of the ernemman f1.8, subsequently all the sonnars plus the biogon
the benchmark wide angle. In a famous article in grossbilde technique in the
fifties he made the statement that fall off from the center to the edge in a
an extreme wide angle lens was inevitable. Light falls off on the square and
the distance from the center of the rear element is way shorter than the
distance to the corner.  He stated that he had managed to reduce modestly
the effect in his design of the biogons,21 to 75mm.  The 35mm apo-grandagon
used in my vistashift-612 cameras, is discussed, illustrated on Robert
Monaghan's benchmark medium format site

http://people.smu.edu/rmonagha/mf/vista612.html  

This lens covers more than twice the area of the famous 38mm biogon on the superwide
hasselbad. It is a superlatively designed lens with amazing lack of
distortion, but without a center filter the light fall is over
 10 to 1. The center is a few mm from the film, the corners on 612 hell and
gone.  If you do your own printing, expose for weak light at the edge
you might away without a center filter.  The 45 apo-grandagon has worked for
me ok w/o a center filter. If you shoot transparencies you should use a
center filter on both, and incidently none of the regular center filters
offered by any one fully compensates for the actual falloff.  As Bertelli
explained you can compensate in the lens design to minimize the effect but
you can't overcome it completely. Now we are at over twice [the] coverage he was
concerned with. Center filters are a wonderful tool. Way back goerz put a fly
swatter in the center of an extreme wide angle.  Vibrating it was supposed
to even out the light. Lots of luck. Hooray for center filters. ralph



From Panoramic Mailing List:
Date: Thu, 14 Feb 2002 
From: Kerry Swartz [email protected]
Subject: Re: XPAN

[email protected] said:

> I'm thinking about buying a Hasselblad XPan, and I remember past discussions
> on this list about it so I was wondering if there is an archive I could find.
> I also heard that the XPan is made by Fuji and that Fuji makes an identical
> camera but they are prohibited from the U.S. market.  I would appreciate any
> comments on the XPan, especially by those who have owned them, and on how to
> get one of the Fujis.  I live across the Detroit River from Ontario -- would
> that help?
>
> Marty

I've had an XPan since they were first released and quite happy with it.

I've used it regularly and it is still in nice shape. My friend bought one
at the same time, has used it less and the finish is awful; I've heard from
others about paint easily chipping off. The 45 and 90 lenses are very good.
I've not opted for the 30mm since it's far too expensive relative to the
price of the XPan body and sell and Xpan which I believe is called the TS1
or something like that. It's silver and usually available in Asian markets.
I've seen the odd one on ebay.

Hasselblad's XPan seems to have the best level of construction when you
compare it to strictly Fuji cameras - more metal instead of plastic, tighter
joins, smoother transport.

The most required accessory would be the graduated center filter for the
45mm lens which allows you to use slide film without much or any falloff,
but you essentially lose a stop or more making it a very slow lens.

I hope these comments find some listening ears since my three repeated posts
about my Olympus E10 appear to have largely gone either unnoticed or ignored
by other members of this list.

Kerry
--
Kerry Swartz [photographer]
online portfolio: http://www.ksphotos.com




From panoramic mailing list:
Date: Thu, 14 Feb 2002 
From: Ted Baker [email protected]
Subject: Re: XPAN

Marty,  I've had an Xpan with 45mm & 90mm lenses for about a year & a half
now & have been totally happy with it.  Design, construction & finish are
excellent.  Kerry Swartz is right -- get the center filter for the 45mm lens
for sure (not needed on the 90mm).  You'll lose a stop but you'll get even
illumination from corner to corner in panoramic mode.  I leave it on the
45mm & have found that I don't need a skylight or UV filter.  I use the XPan
mostly in panoramic mode but being able to switch (even in mid-roll) to
normal mode is a big plus.  If you find someone who imports (on their own)
the TX-1 n the gray market, be advised that you will not be able to get a
Fuji U.S. warranty with it.  Perhaps the importer will offer their own
warranty but I would inquire very closely as to how many TX-1's they have
actually repaired & how many parts they stock.  This is in no way a
criticism of the TX-1, just a heads-up in case it ever needed service.  Feel
free to contact me offline -- I'll be happy to discuss any of the above &
more if you want.
Regards, Ted


Regards, Ted


 "[email protected]" [email protected] wrote:

> I'm thinking about buying a Hasselblad XPan, and I remember past discussions
> on this list about it so I was wondering if there is an archive I could find.
> I also heard that the XPan is made by Fuji and that Fuji makes an identical
> camera but they are prohibited from the U.S. market.  I would appreciate any
> comments on the XPan, especially by those who have owned them, and on how to
> get one of the Fujis.  I live across the Detroit River from Ontario -- would
> that help?



From Panoramic Mailing List:
Date: Thu, 14 Feb 2002 
From: Ted Baker [email protected]
Subject: Re: Center filter for XPAN

Marty,  Center filters are used with any lens that covers a wide viewing
angle to compensate for the falloff of light from the center to the corners
of the image, which is not a defect in the lens design but a limitation of
physics.  A center filter is dark gray at the center & changing gradually in
a radial direction to clear at the edge.  The wider the angle of view of the
lens, the darker the center is.  A center filter is typically matched by the
manufacturer to a particular lens that it will be used with since in general
light falloff varies with each lens.  Thus, I would definitely get the one
that Hasselblad makes for the Xpan 45mm lens.  It has 49mm threads & the
hood for the 45mm Xpan lens will mount on the 45mm with the center filter in
place.  It's Hasselblad part #54453 & you can read a description of it at
this URL:

http://www.hasselblad.com/products/cameras/xpan45.html

The only drawback is that is has a list price of $234.  However, bargaining
with a dealer who wants to make a sale should help a bit.  I'm not positive
what the etiquette on this list is regarding recommending particular dealers
but if you contact me offline I can suggest a good one with reasonable
prices.

Regards, Ted



From Panoramic Mailing List:
Date: Thu, 14 Feb 2002 
From: Peter Marshall [email protected]
Subject: Re: XPAN

...

Marty,

I think it is worth getting an XPan if you get the 30mm lens. The 45mm is
fun to work with, but the 30mm almost gets you into real panoramic
territory. It isn't cheap, though I bought mine secondhand which helped.

A centre filter is essential with the 30mm. With the 45mm you can shoot
without it on colour neg and black and white, but I think you really need
it for transparency, though if you stop down well you might get away with
it.

If I wasn't going to buy the 30mm I think I would be better off with a 120
format camera and a wide angle, cropping down to panoramic format when I
wanted to. Something like a Mamiya 7 with 43mm or 50mm would give similar
results, but also enable me to do other things. And of course there is a
wider range of lenses.

he finish is not too great - I've used mine less than a year and it looks
pretty worn. I think the Fuji is only supported in Japan, which is a long
way to go for repairs.

Peter Marshall
Photography Guide at About          http://photography.about.com/
email: [email protected]




Date: Tue, 19 Feb 2002 
From: Peter Marshall [email protected]
To: [email protected]
Subject: Re: photoshop center filter effect? Re: XPAN

>
> I would think you could take a B&W photo of a uniformly lighted (white)
> wall, scan that negative, and have a custom mask for photoshop exactly
> balancing the dropoff (darker in center as brighter wall)?

It is an idea, and so long as you remembered the diffusion to get
completely rid of any texture would sort of work, though I think the
effect is aperture dependent, so it would only work roughly at other
apertures. You might alternatively just use a mask made using Photoshop's
radial fill with a little tweaking.

There are very few subjects where it is important to get absolutely even
illumination across the frame in any case. I know that it actually is
uneven in my pictures, but it is often not noticeable, seldom disturbing
and in some cases beneficial.

I think you have to remember that many of the people who contribute to
mailing lists are armchair theorists who don't get on with taking
pictures. If you take negatives and get your work handprinted (or do it
digitally) it doesn't seem a big deal to me. I have several hundred rolls
of colour neg that say its not really a problem.

Peter Marshall
[email protected] 



From: "Kerry L. Thalmann" [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: 80mm Super Symmar XL--users? Comments?
Date: Sun, 07 Apr 2002


Just a couple additional data points based on the Schneider relative
illumination curves.  All of the 90mm Schneiders (90mm f8, 90mm f5.6 and
90mm f5.6 XL) have a percent relative illumination in the low 40s (about
40.5% - 44%) at the corners of a 4x5 image (assuming image diagonal of
153mm and no displacements) at f22 and infinity.  By comparison, the
110mm Super Symmar XL is in the high 40s (looks like about 48% give or
take).

For me personally, I've always found a center filter necessary for
anything shorter than 90mm on 4x5.  Specifically, for my personal needs
and sensitivity, I've found the 75mm f4.5 Nikkor SW, 75mm f6.8
Grandagon-N and 80mm f4.5 Super Symmar XL to all benefit substantially
from the use of a center filter.  On the other hand, I've never found
the fall-off sufficient to warrant a center filter on lenses 90mm and
longer.  Based on the numbers, it looks like I am personally willing to
tolerate fall-off in the corners down to about about 40%, but anything
less and I prefer the center filter.


That's just a personal data point, but it does show how you can compare
the fall-off of lenses you are contemplating against ones you already
know.  For example, if I had done this excerise before testing the 80mm
SS XL, I would have already known the fall-off was most likely worse
than the 75mm I'd been using with a center filter (Nikkor SW - which
based on my experience has fall-off very similar to the 75mm f5.5 Super
Angulon and 75mm f4.5 Grandagon-N).  It also tells me that I would
probably require a center filter when shooting 5x7 with the 110 SS XL
(something I've also verified experimentally).

Kerry
--
Kerry L. Thalmann - Large Format Images of Nature
http://www.thalmann.com/

Kerry's Large Format Homepage
http://www.thalmann.com/largeformat/



From panoramic mailing list:
Date: Mon, 01 Apr 2002 
From: ralph fuerbringer [email protected]
Subject: Re: Low tech question.

Medium tech filter and ring info, many are unaware of: in respect to wide
angle lenses, many lose image circle when you screw anything into the front
threads, not that swinglens cameras have/need wide angle lenses at all. I am
referring to the super angulons, apo-grandagons, super symmar xl aspherical.
only rodenstock mentions this problem, publishing these startling,
threatening figures: the 55mm apo-grandagon loses 9mm from the diameter of
its image circle and its angle is reduced from 110 to 107 degrees when its
dedicated center filter is screwed in. you buy a center filter to get better
edge coverage, but hey catch 22 the far edge is eliminated altogether  by
the filter.  Further degrading of the image is from reflection of the screw
in ring on the film,this also in the rodenstock center filter brochure.

solution: for my vistashif-612 tweak of the brooks veriwide
(http://people.smu.edu/rmonagha/mf/vista612.html) i use over the lens filter
mounts, into which i remount the center filters. all center filters are
actually in step up rings to begin with. For example the dedicated center
filter for the 55 apo-grandagon has the 67mm lens threads on the small end
and 86mm on the front.  also in many the retaining rings are way to wide and
again can cut image. heligon center filters are the worlds worst in that
regard.

ralph

> From: [email protected]
> Date: Mon, 01 Apr 2002 
> To: [email protected]
> Subject: Re: Low tech question.
>
> I said adapter rings, I meant to say step-up rings.
>
> AJ




From: [email protected] (Richard Knoppow)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: Newbie Questions- Soft focus and Center Filter
Date: Fri, 17 May 2002


[email protected] wrote:

>First what is a soft focus lens?
>Second, what is a center filter and why do they cost so much?
>
>Thanks,
>Keith Mitchell
>[email protected]

....(soft focus..)

  Center filters are made to correct, at least partially, the fall off
of illumination from center to edge of an image. This fall off is an
inherent property of lenses which are made to reproduce a flat surface
onto another flat surface without distortion, a property called
rectilinear. Most camera lenses are designed to be rectilinear. An
exception is the fish-eye type wide angle lens. Because the image is
compressed toward the edge (it looks as though one were seeing it
reflected in a sphere) there is little fall off.

  Some lenses employ a principle called a tilting entrance pupil,
which effectively makes the lens faster for light coming in at an
angle. This principle can partly correct fall off, but most of it
remains. For lenses with more than moderately wide angle coverage the
darkening of the image away from the center can become important,
espeically when using positive color film. So, a center filter is used
along with stopping down the lens. The center filter allows more light
to enter at angles from the edges and reduces the light at the center,
making it more uniform.

  Center filters must, in general, be matched to the lens they are
used with in the sense of the size of its front element and coverage
angle. They do not have to be made specifically for a particular lens.

  The center filter should also be matched to the fall off rate of the
type of lens its to be used with.

  Center filters are expensive partly because they require some
precision in manufacture. The coating must be color neutral and effect
all colors to which film is sensitive. It is generally a vacuum
deposited metal film. In order to work properly it must taper from
center to edge in a prescribed manner and to a precribed density. Not
cheap to make. They are also generally made in small numbers so
whatever savings might be made from mass production techniques is not
available.

  Keep in mind that the integrated circuits used in electronics would
cost a fortune if made in small quantity, they are very cheap because
they are made by the ton. This sort of economy is not available to
something as specialized as a center filter.

---
Richard Knoppow
Los Angeles, CA, USA.
[email protected]


Subject: Re: advice needed on centre filter for 58mm SA XL
From: Jon [email protected]
Newsgroups: rec.photo.equipment.large-format,[email protected]
Date: Fri, 19 Jul 2002


Hi Wayne,

I just bought the Schneider 3B center filter for my 58mm SAXL. It is of a
very good quality.

I didn't find this to be much help:

http://www.schneideroptics.com/photography/accessories/center_filters/

But B&H's web site says this:

67mm Center Filter (#3b) for 80mm f/4.5 and 110mm f/5.6 Super Symmar XL
Lenses and 58mm f/5.6 XL and 90mm f/8 Super-Angulon Lenses

I don't know if the 3B will work on the Sinaron... does it really need a CF?

The 58mm SAXL definitely needs the CF on 4x5--I have found it necessary also
when shooting chromes with lots of sky on 6x12.

Jon

P.S. You may have a tough time getting a filter on the front of the CF
(86mm). Schneider told me that only the EW series will work with CF's. I had
Steve Grimes make me a slip on mount for 4x4 (100mm) gels. It was cheaper
than the one glass screw-in filter I was going to buy and it took him a week
to make it.

Here:

http://www.skgrimes.com/

> From: [email protected] (Wayne Stubbs)
> Newsgroups: rec.photo.equipment.large-format
> Date: 18 Jul 2002 
> Subject: advice needed on centre filter for 58mm SA XL
>
> I have just purchased a 58mm xl lens. In the next couple of weeks I
> will be buying the centre filter for the lens. I understand that this
> filter can also be used on the 90mm f8 super angulon as well.
>
> I also have a Sinaron 75mm f4.5 lens. Does anyone know wether the
> schneider centre filter will work well with this lens ?
>
> As anyone tried to do this and got exceptable results ?
>
> many thanks,
>
> Wayne Stubbs


From camera makers mailing list:
Date: Tue, 03 Sep 2002 
From: Robert Mueller [email protected]
Subject: Re: [Cameramakers] Re:  Resolution of Metrogon

Thanks for the advice on the center filter for the Metrogon.  I actually
had a different problem in mind.  As I understand it a piece of flat glass
adds spherical aberration.  Someone in this group reported that the
Metrogon was calculated with this in mind by including compensating
aberration of the opposite sign so optimum resolution would be reached when
one of the center filters was in place.  (These things are pretty
thick.)  Conversely, I have a publication (in fact, two of them) giving
data for the glasses, radii and spacings of the Metrogon and neither
mentions any filter.  Then again, just because the published designs do not
include a center filter does not mean B&L did not tweak the design for the
military optics.  Thus, I simply have no idea how much difference the
filter makes and, sadly, I have never seen a clear center filter for these
lenses.

What you report on the importance of uniform exposure is very revealing and
makes clear why looking only at resolution data is a mistake and the whole
situation must be considered in the context of making real photos.

Thanks again!

Bob

you wrote:
>resolution could actually be higher with the center filter, since excess
>exposure (1 stop) can cost you 20% or more of resolution potential, per
>example tests cited at http://medfmt.8k.com/mf/lenstest.html by Roger Hicks
>in Jan 2002 Shutterbug in testing wide angle 21mm on Pan F film. If the
>center filter enabled uniform exposure without a center highlight, you
>would avoid these losses (and more likely 2 or more stops overexposed without
>the filter, so even more of a resolution hit?).
>
>The losses from a decent flat filter to MTF is on the order of 2% or so
>for a good filter, and for a cheapy no-name not so flat filter, maybe 10%
>at high end, per Erwin Puts estimate (he is a noted Leica lens testing
>guru etc. However, this assumes that any focus shifting effects of the
>filter are compensated in setup.
>
>I find this a bit disconcerting (and not often discussed, hence notable), as
>it means relatively minor exposure errors or differences between systems (and
>by implications, developing differences between runs) can have as much of an
>impact on lens test results as the differences between mfgers (e.g. Leitz R
>vs Nikon etc. ) ;-)
>
>But my bet would be that the impact and benefit from avoiding  over/under
>exposure would outweigh the minor losses from the filter itself...
>
>* Robert Monaghan 


From camera makers mailing list:
Date: Wed, 04 Sep 2002 
From: Michael Briggs [email protected]
To: [email protected]
Subject: [Cameramakers] Re: Cameramakers digest, Vol 1 #474 - 7 msgs

[email protected] wrote:
> Thanks for the advice on the center filter for the Metrogon.  I actually
> had a different problem in mind.  As I understand it a piece of flat glass
> adds spherical aberration.  Someone in this group reported that the
> Metrogon was calculated with this in mind by including compensating
> aberration of the opposite sign so optimum resolution would be reached when
> one of the center filters was in place.

I assume that the center filter is used in front of the Metrogon?  If so, then,
for the photography of distant objects, the mere fact of having a flat uniform
thickness filter in front of the lens does NOT introduce spherical abberation.
For distant objects, the arriving light rays are very close to parallel -- the
effect of a flat uniform thickness piece of glass on parallel light rays is to
slightly shift the rays in a parallel manner -- with an object at infinity this
isn't noticeable.

Conversely, if a flat uniform thickness piece of glass is inserted into a beam
of convergent rays, spherical abberation will be created.  This would be the
case for a filter behind a lens, or a filter in front of a lens when the lens
is focused on a close object.   If you are doing closeups or using a filter
behind a lens, you should focus with the filter in place -- it changes the
apparent distance.

Compared to other filters, a center filter has some complicated effect on
abberations.   If you a lens without a center filter, the light rays that reach
the film have arrived with equal probability over the front of the lens (at
least the part of the glass used at the taking aperture).  If you use a center
filter, then the light rays at the edge have a higher probability of reaching
the film.  If the abberations contributed by the outer radii are different from
the inner, then the mean abberation will be changed.   I don't think there is
any simple way to predict this effect.   For a really wide-angle lens, the
improvement in exposure uniformity due to using a center filter is likely to be
more important.

--Michael


From: Bob Salomon [email protected]
Newsgroups: rec.photo.equipment.large-format,rec.photo.equipment.medium-format
Subject: Re: Where to buy Schneider or Rodenstock filters?
Date: Tue, 08 Oct 2002

 [email protected] (Xosni) wrote:

> I'm fed up with those Hoya filters. I want to try quality filters now-
> I'm talking specifically about #29 (dark red) filter for B&W. Where
> can I get Schneider or Rodenstock filters in the US (VA)? And which
> offer the best quality?
>
> regards,
> Xosni


Rodenstock only makes Graduated Center Filters. All other Rodenstock
filters are Heliopan.

--
HP Marketing Corp. www.hpmarketingcorp.com Ansmann, Braun, Combina,
DF, Ergorest, Gepe, Gepe-Pro, Giottos, Heliopan, Kaiser, Kopho, Linhof,
Novoflex, Rimowa, Rodenstock, Sirostar, Tetenal ink Jet and cloths,
VR Frames, Vue-All archival products, Wista, ZTS



Date: Thu, 24 Oct 2002 
From: Jim Brick [email protected]
To: [email protected], [email protected]
Subject: Re: [HUG] Scanning Xpan 35mm Negatives

Manu Schnetzler wrote:
>Actually, Epson TWAIN doesn't have any problem with arbitrary size. I've
>scanned xpan negs with it with good results (such as
>http://www.schnetzler.com/PAW/week_39.html).
>
>The only problem I see is a bit of vignetting but that's a due to a lack
>of center filter on the camera, not to the scanner.
>
>Manu


Over the years, some of my best (and most sold) photographs are those taken
with a very wide angle lens and no center filter. The edge darkening quite
often (most often for me) enhances the photograph, especially when printed
20x24 or 30x40. You don't really notice the drop off around the edges but
it really helps to keep your eyes focused within the image rather than
having them run off the edge of the print.

You Xpan photograph (very nice photograph) falls into this category in my
view. The drop off is good.

:-)

Jim


From: "John Cremati" [email protected]
To: [email protected]
Subject: Re: [Cameramakers] center filter
Date: Tue, 7 Jan 2003 


      Rather than using a silver based emulsion as the final emulsion or
film  , you could use a  glass coated with gelatin with a aniline dye (
aniline dyes are  generally transparent) , sensitize the emulsion with
ammonium dichromate .. Aniline dyes I believe is what Kodak uses in many of
their gelatin filters.. The first image would be silver based fine grained
negative film but then you would contact print the gelatin dye coating to
create the filter.. In essence what you are doing is making a carbon print
of the light fall off.....

     The big problem would be to determine which dye has the neutral density
characteristics...Creating a center filter in red, yellow , orange or green
filter would probably very easy  information to come by as isochromatic
photography is based on  the various dyes ability to absorb different parts
of the spectrum of  light.., but I would not even know where to begin on 
creating a neutral density dye...

Another problem would be to make the filter so the fall off is equal to that
of the lens when placed in front of it....

 jc  


Date: Wed, 05 Mar 2003 
From: Robert Feinman [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Fixing wide angle vignetting using Photoshop - New Tip

I've added two new tips on adjusting darker corners when using ultra
wide angle lenses or wide aspect ratio formats to my web site. Using
Photoshop can help avoid needing a center filter.

I've also updated some of my Hawaii photos taken with my 4x5. The
views of the interior of the Haleakala volcano crater came out quite well.

Finally, a little off topic. If you need a change from lugging all the
large format equipment around you might be interested in my ebay
auction of a Tessina 35mm subminiature camera. Smaller than a pack of
cigarettes.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2915505279
--
Robert D Feinman
[email protected]
Landscapes, Cityscapes, Panoramas and Photoshop Tips
robertdfeinman.com


Date: Thu, 10 Apr 2003 
Newsgroups: rec.photo.equipment.medium-format
From: Gavin Shaw [email protected]
Subject: Re: Graduated ND Filter for G617 via photoshop layer?

from [email protected] (Larry) contains these words:
> Hi,
> I would like to construct an accurate photoshop layer
> that can be used as a post-processing fix up in place of
> a real graduated neutral density filter. For Fuji G617 with
> 105mm F8.
> Yes, I recognize it is not the same as a real filter and
> the exposure can't be as accurate.
> I use color print film.
> I would try to hit perfect exposure for a point halfway between the center
> and the ends. Then slightly darken
> the center and slightly brighten the two ends. With even gradation
> in between.
> Would the values be a function of the F stop? Or is the drop off consistent
> despite aperture changes.
> Any tips appreciated.
> thank you
> Larry

Larry,

There's a tutorial using a multiplication layer for your very lens on
Luminous Landscape:
http://www.luminous-landscape.com/tutorials/panorami.shtml

I expect the graduation could change slightly with F-stop. Maybe you
could create an empirical multiplication layer for a range of F-stops
by photographing an evenly lit plain surface, scanning it, softening it,
inverting it. Tricky to find something big enough to photograph without
close focus capability, but I guess you wouldn't need an in focus
surface!?
--
Gavin
http://www.users.zetnet.co.uk/gshaw/


[Ed. note: thanks to Robert Mueller for sharing these ideas and tips...!]
From: Robert Mueller [[email protected]] 
Sent: Fri 5/30/2003 
To: Monaghan, Robert 
Subject: Center Filters not at the center!

I have long been longing for a clear center filter for my Metrogons and
just read through your collection of postings on the
subject. Unfortunately, I don't know the correct way to add to the
material so I am just making a suggestion for a different, though limited
approach.

Making a proper, graded center filter is not easy and designing it
(figuring out what the optical density versus radius must be) is also not
trivial as far as I can see. In the above comments I saw some worries
about the "flower pedal" style of filter but some of the concerns seem
excessive. For example, if you "glue" a foil to the glass of a large,
clear filter, I see no need to worry that the foil be precisely flat if it
is truly opaque. It would help to have the foil black but with aluminium
that is easy to achieve; black anodize, practically a household operation,
though you need a suitable power supply. If you are careful you can
remove the foil and try again until you reach adequate uniformity. I do
not completely share the concerns about loss of resolution; such an effect
will result from extra diffraction but the B&L filters were good enough for
the military aerial photos and the military is not well known for making
compromises. A few extra thousand dollars for a graded density filter
would upset nobody if the results were substantially better. According to
one book I have, astrophotographers find the Metrogons not so good unless
stopped down somewhat (but that information is ancient and may apply to the
4 -element variety only; I don't know!) For this small aperture
diffraction from the "pedals" might just disappear into the background of
the diffraction from the lens itself.

For those who want a nicer end product, after determining the correct pedal
shape, you can deposit silver onto the well cleaned glass (the way mirrors
were once made) and etch away what is not required to leave the correct
pattern. The bad news is that this is not black on the lens side, but I
suspect the B&L filters are also mirror-like, though the metal is probably
chromium or Inconel, which adhere better (chrome is wonderful and I have
been able to wash glass with this coating without loss of the chrome or
other damage.) I believe Inconel is especially useful if you attempt the
graded filter type of center-filter because the color is quite neutral;
however, I have great doubts there will be many graded, evaporated filters
made by readers of this group. The equipment and skills are probably quite
rare.

If anybody has one of the asterisk-type ("Flower pedal") filters it would
be wonderful if a photo could be posted showing as precisely as possible
how this should be shaped. A size reference would be highly desirable.
Better would be a precise drawing but that needs more work so probably
nobody wants to make it.

For the occasional camera offering no swings, tilts or other movements and
only used at a fixed object distance (infinity is fixed enough!), why not
put a filter at the film plane! There the demands on optical quality are
easier to meet and the density is easy to determine. Photograph a wall and
measure the density versus position (really only density versus radius
ought to be needed unless something is wrong, a simple, one-dimensional
problem.) I would even try just producing this density function from a
photo of the wall and with appropriate processing to get the correct gamma
and center density. Then use this just in front of the film, not up front
at the lens. I admit the loss of flexibility going with movements is not a
trivial matter but some camera already sacrifice the flexibility and there
the method might be a quick and dirty way to accurately flatten the
exposure over the film area. Something similar to this was suggested
above but to be placed at the lens. Here the demands on optical quality
are much more stringent, the main motivation for moving the filter to the
film plane. It is probably better to use color film for this job because
the pattern will be in transparent dyes, but there is a major problem, the
masking tint in the film base of negative materials. (Positive materials
have a clear base but put the most light in the middle, exactly what is
unwanted.) Dyes will scatter light less than the tiny grains of silver in
black and white films, though with the filter near the film to be exposed
this should not be too bad. I believe there are some rare film types
making negatives in color without the masking color.

The above mentioned constraint on distance is weak; close-ups would be a
problem but I expect no serious trouble at reasonable distances. Using a
very wide angle lens for close-ups is probably not too common; though I can
imagine applications where it is the best (only?) solution.

Bob
 falloff pattern,
>which can be imaged negatively to yield ideal center filter pattern, yes?
>;-) the trick is to get the right magnification, which is to say, to
>reverse the light thru the negative, back thru the lens, with a "filter"
>of the right size in place. The filter could be a sensitized UV filter,
>sensitized by liquid emulsion, yes? Then develop it, to get a "negative"
>of the negative, that is, the positive center filter image you need.
>This assumes you can shine light thru the negative of the uniformly
>lighted wall, back thru lens, to sensitized filter in front of lens. It
>doesn't have to image at infinity, it should be the right size and density
>for near infinity (or wall distance etc.)?
>
>If you can find a film base that is clear enough, and many films are
>pretty decent, including slides ;-) you can simply
>try the above with the film and use the developed film in an empty filter
>ring, yes?
>
>just some late night thoughts - gotta run, closing up the bldg here ;-) bobm
--->


From: "Nicholas O. Lindan" [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: More cheap 8X10 center filter ideas?
Date: Fri, 18 Jul 2003 

"J Stafford" [email protected] wrote
> Forgive me for being little off-topic, but making up for light fall-off
> during the printing rather than using a graduated filter in the making of
> the image is wildly different in terms of outcomes. In the printing method
> one part of the negative is either over exposed or underexposed, so the
> curve (gamma?) is off.

Yup.

To have a chance of working this technique would require using a straight-
line film (constant gamma: no shoulder) with great latitude. Tmax-100?

I would recommend trying it - shouldn't take more than an hour or two
of darkroom time and 2 sheets of film. 

Looking at:

http://www.kodak.com/global/en/professional/support/techPubs/f32/f002_0545ac.gif

and doing a bit of work with ruler and pencil, I come up with the following steps
making the center filter:

Develop for 9 minutes - this produces a 1:1 slope so that doubling the exposure
doubles the density

Expose in the camera so the corner of the negative has a density of 0.8 OD -
this point is the beginning of the film's linear response.

Expose the positive filter so the center is at 0.8 OD.

That should do it.

Success is achieved when a sandwich of the negative and positive
filter films yields a uniform grey, yah?

When taking pictures one again has to use T-Max 100 developed for 9 minutes
in T-Max RS at 75F.

The developer doesn't have to be T-Max RS (though it is the one Kodak recommends
for the most linear response).

Yeesh - time to stop talking about it and just do it. Paralysis by
analysis is what we have here.

--
Nicholas O. Lindan, Cleveland, Ohio [email protected]


From: [email protected] (ArtKramr)
Newsgroups: rec.photo.equipment.large-format
Date: 18 Jul 2003 
Subject: Re: More cheap 8X10 center filter ideas?

>Subject: Re: More cheap 8X10 center filter ideas?
>From: [email protected] (J Stafford)
>Date: 7/18/03 
>
>Stacey [email protected] wrote:
>
>> I've got an old brass wide angle lens for my 8X10 that is interesting but
>> has a bunch of light fall off. I'm thinking there must be a way of
>> making/using a "center filter" in the enlarger I use as a light source for
>> contact printing,[...]
>
>Forgive me for being little off-topic, but making up for light fall-off
>during the printing rather than using a graduated filter in the making of
>the image is wildly different in terms of outcomes. In the printing method
>one part of the negative is either over exposed or underexposed, so the
>curve (gamma?) is off.

Corner fall off means information is lost in that area. Trying to correct it on
the printing does not bring back that information. It MUST be corrected in the
shooting or it will not solve the corner fall-off problem as far as information
in the corners is concerned..

Arthur Kramer
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer


From: [email protected] (ArtKramr)
Newsgroups: rec.photo.equipment.large-format
Date: 16 Jul 2003 
Subject: Re: making a center filter

>Subject: making a center filter
>From: Robert Feinman [email protected]
>Date: 7/16/03
>
>I've always thought it might be possible to make a
>center filter yourself, rather than pay the $$$ that
>they cost.
>The idea would be to photograph a uniform surface
>which would produce a negative with a darker center.
>This would then be cut to size and mounted in front
>of the lens. Being close to the the lens it would be
>out of focus and thus the grain wouldn't affect the
>image.
>The difficulty comes with trying to get the scale
>of the negative right as well as the density and
>contrast.
>Any thoughts?
>
>I've devised a proceedure using photoshop to correct
>vignetting, but it relies on film latitude to capture
>the brightness range and thus isn't good for transparencies.
>You can read about it in my tips, if you're interested.
>--
>Robert D Feinman
>[email protected]
>Landscapes, Cityscapes, Panoramas and Photoshop Tips
>http://robertdfeinman.com

Simple. Do this. set up your camera in front of a white or gray sheet. Using
the lens you want to correct make an exposure where the center of the image ia
a middle gray. Develop the film. The image on the film now represents the
falloff of the lens. Now make a reduced image to fit the lens. You now have a
reasonably good center filter.

Arthur Kramer
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer


From: John Stafford [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: making a center filter
Date: Wed, 16 Jul 2003 

Robert Feinman wrote:
> I've always thought it might be possible to make a
> center filter yourself,[...]
> The difficulty comes with trying to get the scale
> of the negative right as well as the density and
> contrast.
> Any thoughts?

A center filter need not be graduated. You can have, for example, an
evenly filled, transparent, symmetrical star-like shape imprinted upon
or placed upon a clear filter. I can post a scan of just such a filter
this evening if you like.


Date: Wed, 16 Jul 2003 
From: Robert Feinman [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: making a center filter

I've always thought it might be possible to make a
center filter yourself, rather than pay the $$$ that
they cost.
The idea would be to photograph a uniform surface
which would produce a negative with a darker center.
This would then be cut to size and mounted in front
of the lens. Being close to the the lens it would be
out of focus and thus the grain wouldn't affect the
image.
The difficulty comes with trying to get the scale
of the negative right as well as the density and
contrast.
Any thoughts?

I've devised a proceedure using photoshop to correct
vignetting, but it relies on film latitude to capture
the brightness range and thus isn't good for transparencies.
You can read about it in my tips, if you're interested.
--
Robert D Feinman
[email protected]
Landscapes, Cityscapes, Panoramas and Photoshop Tips
http://robertdfeinman.com



From: stacey [email protected]
Newsgroups: rec.photo.equipment.medium-format
Subject: Re: Mamiay 7 43mm- was Camera suggestions?
Date: Wed, 29 Oct 2003 

Bill Hilton wrote:

>>>Bill Hilton wrote:
>>>
>>> Mamiya can do this with this lens because
>>> there's no mirror in a rangefinder and the effect apparently is to
>>> greatly reduce distortion and light fall off
>
>>From: stacey [email protected]
>
>>It may reduce distortion but it DOESN'T reduce light fall off, if anything
>>it will have more.
>
> "More" than what? I don't see any problems with mine, even shooting a
> place like White Sands, where fall-off should be readily evident.

Well another poster who uses this lens said he needs a center filter to get
rid of =all= of it. It may not be visible in many of your uses and neither
is it visible with SLR wide angles in many uses, but it is there.

>
> Do you actually have this lens or is this just a theory of yours? If you
> have it can you post an example showing the problem?
>


Chill out dude.. ANY super wide lens is going to have some light fall off,
it's against the laws of physics for it not to, no matter how much you paid
for it! A non-retrofocus lens doesn't avoid the cos^4 law in fact is likely
to suffer more from it than a retro focus lens would be, but the retro
focus will have more distortion.

Here's a post I found doing a google search, I'd assume a 90mm on 4X5 isn't
even as wide as the lens you're talking about?

-------------------------

Dean Shough , jul 01, 1999; .

The standard formula for off axis light fall off is (cos(theta))4. A 4 by 5
inch piece of film has a diagonal of 6.4 inches = 163 mm. The angular half
field of view for a 90 mm lens is arc tan( 0.5 * 163 mm / 90 mm ) = 42
degrees. Cos(42 degrees) = 0.74. Raise this to the fourth power and the
corners receive 30% of the light the center receives - almost two stops
less than the center! If the lens is tilted or shifted, the fall off will
be worse.

Some notes on the cos 4 light fall off:
This is for an ideal lens with no vignetting.
Closing down the lens will help only if the lens is vignetting.
One cos factor comes from the obliquity of the circular aperture - the
aperture appears to be an ellipse to the off axis ray.
Another factor of cos comes from the light striking the film at an angle.
Two final factors of cos come from the increased distance between the
aperture and the off axis portion of the film being illuminated.

Some lenses differ markedly from the cos 4 value, even after accounting for
vignetting. This can be caused by pupil distortion and image distortion.
Many super-wide angle lenses, especialy ones for 35 mm cameras, are
designed so that the aperture (pupil) appears larger as you move off axis.
This allows more light to reach the corners of the film. Likewise, extreme
barrel distortion (think fish-eye) increases the intensity near the edge of
the image.


Yet another way to cheat on the cos 4 fall-off is to use curved film.
Classical Schmidt cameras (telescopes) use have a curved film plane that
eliminates #4 and #5 above, so that the light falls off only linearly with
cos.
------------

That said I've never been bothered by the slight fall off my 90mm has on 4X5
but some people are..
--

Stacey






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