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Zig Align tool (for enlargers etc).

In case you haven't seen this accessory, it is used for ensuring precise alignment between the camera's film plane and the (flat) object to be photographed. Major uses are in photographing artworks (e.g., flat paintings, etchings, drawings..) and documents. The key value is in ensuring that the film and the flat object are in precise alignment. When so registered, you don't get any of the key-stone effect or converging of horizontal or vertical lines which should be parallel that you might otherwise see (as distortion). A similar device is also used for aligning enlargers.

The principle is derived from those trick optical illusions where four (front surface) mirrors are aligned parallel to each other inside a box with some small figures (or even people in a larger version) are inside the box. Looking in from the top of the box, you will see a seemingly infinite number of figures branching off in rows and columns to infinity. What is happening is that the light is bouncing back and forth from the parallel mirrors again and again, creating this illusion. If the mirrors are mis-aligned, the images will seem to go uphill or downhill depending on the alignment errors. This simple setup is an extremely accurate way to achieve alignments within a few minutes of arc or better (e.g., one in 10,000 accuracy).

A collimator is a related device that uses somewhat similar principles to test lenses. As an aside, a simple collimator can be built from the objective and eyepiece of a binocular, a front surface mirror, and a half-silvered mirror such as you can find in rangefinders. Here again, the light bounces back and forth (to "infinity") between these two mirrors, permitting precise lens testing (at "infinity" optically but on a workbench physically). Tomosy's camera repair book describes an inexpensive homebrew collimator using such modest cost items. You can probably use a half-silvered mirror as an alternative to removing some silver from the mirrors in the design described below too. Some surplus shops offer these parts inexpensively (see surplus shed and related links at Impact! photo dealers pages).

The versions of mirror alignment devices made by Hasselblad and other medium format and large format mfgers are hard to find specialty items and rather expensive (e.g., $300 US). Oftentimes, one mirror goes on the film plane with the removable back or ground glass removed to permit this setup. On a 35mm SLR camera version, you would need to mount the camera body on a rigid tripod and open the camera back. Now put one of the mirrors on the film plane where the film would go for alignment (then put in film and shoot).

The other (non-see thru) mirror is hung (on a plumb line) or placed on the object (or a flat rule placed over a flat frame etc.). In doing a lot of document copying, you can create a setup to permit rapid centering and alignment of paintings, prints, etchings, or other documents on a flat surface. A cross on a flat surface can be used to align the document or artwork so it is centered and ready to be copied. Before shooting, the alignment tool is put on the center of the cross and the mirror mounted on the camera film rails. The alignment tool is used to ensure that the camera as setup is in perfect parallel alignment of the film plane to the centered document or object. Now remove the alignment tool and replace the film back (e.g., on a Hasselblad or other medium format camera's back) or film pack (on 4x5 inch view cameras) and shoot.

The camera is adjusted until it is aligned, as shown by a large number of concentric circles as the image of the first circle is bounced back and forth by the aligned mirrors. If the mirrors are not in exactly parallel alignment, the circle images move off to one side. The mirrors then still have to be brought back into alignment. Since you generally want to align the center of documents or artwork with the camera, you may find our tips on our art photography pages useful for some situations where moving the artwork isn't feasible.

The very handy homebrew tips below by Michael Gudzinowicz show how relatively easy and low cost it can be to build such a device!

Date: 18 Jan 2000
From: [email protected] (Michael Gudzinowicz)
Newsgroups: rec.photo.equipment.large-format
Subject: Re: SOTP: mirror alignment device?

Sean McEntee [email protected] wrote

> I seem to recall seeing a device that used a pair of mirrors to precisely
> align front and rear standards on a view camera to check parallel, or lens
> stage and neg stage and baseboard parallel.
> I thought it went by the name "mirralign".
> Does this ring any bells?  I have to do some tweaking to my new enlarger
> and thought about giving this thing a whirl, instead of endless fidgeting
> with a torpedo level.

The name doesn't ring any bells, but similar devices are easy to make. Simply get two mirrors, draw or paint a circular ring on the front of one, and in the center of the ring partially remove some of the silver to create a "peephole". When you look through the hole, you will see a series of concentric rings reflected back and forth between the mirrors when they are parallel. When they aren't parallel, the rings are not concentric.

If you use mirrors which are approx. 4"x12", you can place one end on the negative stage, and place the other against the lensboard or on the baseboard. The alignment between the negative stage and the lensboard or front of the lens is very critical, since tilt will throw off the plane of focus at the baseboard even if the carrier and baseboard/easel are aligned. After the lens and negative stage are aligned, align the stage and the baseboard. Recheck, and check the lens/lensboard alignment with the baseboard just to be sure everything is all right. You may need to place a bright light between the mirrors and just off to one side to see the multiple reflections clearly.

The same principles apply to aligning a camera to a copyboard. With an SLR, you just need to place a mirror on the copystand and look through the finder and align the image of the front of the lens.

From: [email protected] (WOrford204)
Newsgroups: rec.photo.equipment.large-format
Date: 21 Jan 2000
Subject: Re: SOTP: mirror alignment device?

>I thought it went by the name "mirralign".

The name you are looking for is 'Zigalingn' They make alingment tools for enlargers and cameras. I have one for my cameras and its works very well.

Regards Bill Orford

Date: Tue, 18 Jan 2000
From: Bob Salomon [email protected]
Newsgroups: rec.photo.equipment.large-format
Subject: Re: SOTP: mirror alignment device?

Try Zig-a-line they are in San Francisco and have both parallel mirror and laser alignment systems.

....

From hasselblad mailing list:
From: Frank Filippone [[email protected]] 
Sent: Mon 11/24/2003 
To: [email protected] 
Subject: RE: [HUG] RE: Pointing - Mirror device


 
If you wish to make your own......

Get any old filter that fits the 38mm lens you have. Remove the glass (
break it if needed).

Find someone to cut a piece of mirror to the right diameter to fit inside
the filter.. or if the mirror is too thick, you can glue it to the outside
of the filter ring. Note that if you decide to use the glue on method, the
filter does NOT need to be broken. YOu cans use the filter with the old
colored glass.

Drill small hole in center of mirror..... this is the hard one.... you will
need a special drill bit and a drill press.
Glue or mount mirror to lens.

Focus camera using ground glass.
Second mirror is held in the same plane as the object you are photographing.
Look through the SWC lens. When you see concentric circles, your camera is
parallel to the object you are photographing.

Frank Filippone
[email protected]