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From: [email protected] (Askcmraguy)
Newsgroups: rec.photo.equipment.medium-format
Subject: Focus problems: The article they wouldn't (didn't dare) print
Date: 3 Mar 1999

"I've read and saved your articles in (magazine) and want to know if you can help me with a problem," the voice implored over the phone. "You seem to understand and know how to solve photographers' problems and I've got one that (a respected East Coast company) couldn't repair. Would you look at it?"

Bob Annucci of Bernadette Lee Photography Studio, Philadelphia, Pa., then proceeded to explain his problem with strange out of focus areas in his Mamiya RB67 negatives. Before he finished talking, I was quite sure what was causing the problem. It's a problem I had encountered many times with not only Mamiya equipment, but Bronica and Hasselblad equipment, too.

Another situation, much earlier - in August 1996, with a Hasselblad focus problem was brought to me. The owner of the 500 C/M was getting areas of softness in his negatives. He noticed the problem was intermittent and usually occurred when he tripped from the body release (the camera was on a tripod). However, when he used the mirror-up position before pressing the body release the negatives were almost always sharp - "almost always" were the key words.

Because the mirror-up position gave the greater percentage of sharp images, he looked for a cause. He felt the film was being pulled out slightly when the blackout flaps opened up, and they do create a "vacuum" as evidenced by holding a sheet of paper near the back of the camera, then tripping the release. If the paper is placed the same distance from the flaps as the film is in the film back, about 6 millimeters (one-fourth inch), the paper is indeed drawn to the camera back. Studying that premise, I worked with an old body and back to study the force of the vacuum action on the film. That ended when I remembered his images weren't always sharp with the mirror up. There is much, much more to this than just the flaps' action. I looked closely at the Bronica and Mamiya blackout cover action. The air draw with them is negligible because the blackout cover is operated at an angle away from the film; the air eddies as the cover swings up.

Things were now coming together rapidly as I studied the back focus problem more closely and thought about repairs I had done and what was involved.

Over the years, I have discussed negative sharpness with scores of photographers. Some observations stood out that were unique to Hasselblad owners. Soft, or out of focus images in high humidity conditions; areas in the focus plane were out of focus, while the rest was sharp; lower part of the image was out of focus and the upper was sharp. Generally speaking, the photographers "blamed themselves" for the focus problem, thinking they had "done something wrong." They reconsidered their thoughts after I asked them how they could have caused those unusual focus problems. Most merely accepted the phenomenon as "things happen." They would work around the problem, for instance, by making additional images when the humidity was high to ensure enough sharp ones.

Curiously, this wasn't a problem for Bronica and Mamiya owners. When it did occur, the problem was correctable, which I will discuss later in this article.

Inarguably, Hasselblad (Zeiss) lenses are the sharpest made. Also, the Compur/Prontor shutters made for the Hasselblad lenses enjoy the greatest longevity of all shutters I have serviced for almost 40 years. However, lens sharpness is only as good as film will record; film must lie flat in order to record a sharp image. (Yes, there are other factors involved; but for the sake of discussion, those factors are considered equal.)

Let's go back and examine Bob Annucci's focus problem. The company's service department told Bob that his RB67 Pro "body casting bent" which, supposedly, caused the focus problem. I told Bob that such a condition was highly improbable because it's impossible to have a bent casting without outside physical evidence of impact; and if such an impact occurred, it is doubtful the body would operate. He sent me a sample print, the lens, body and back. There was nothing wrong with the body other than needing maintenance. The lens, considering its age, was fine - just needed normal maintenance. The old 120 Pro back - well, that's another story. It needed service and the focus problem practically pointed to itself: the spring behind the pressure plate was fatigued from age and couldn't hold the film firmly against the film plane. As I advanced film through, I could see it buckling and rippling. No wonder the negatives couldn't record a sharp image! The repair work commenced and included restoring spring pressure on the pressure plate. Bob reported that his images are once again tack-sharp just like they were before. He then sent his other old 120 Pro backs to be gone through. They, too, had fatigued pressure plate springs. The old Pro backs are not alone with this problem. The Pro-S backs have been around for about 20 years. I have found many of the older ones, about 15 or more years old, having pressure plate spring fatigue.

Bronica film backs experience the same problem, except I've had to make the pressure adjustment with backs that were only about five years old.

It's time to go back to the Hasselblad back problem where "almost always" the negatives were sharp when using the mirror-up position. I did a test that you can also do: line up Bronica, Mamiya and Hasselblad backs with the dark slides removed and pressure plates facing up. Press down on the Bronica plate - it should feel firm; press down on the Mamiya plate - it, too, should feel firm; press down on the Hasselblad plate - it probably feels like pressing down on a marshmallow.

Is the picture beginning to come into focus? The pressure plate must have pressure to hold the film firmly against the film plane!

Since August 1996, four photographers who have experienced out of focus/soft images with their Hasselblad backs have each been field-testing one of their backs that had "the problem" that I modified for them. They had no clue as to what I did to their backs. All they had to do was to keep me apprised of any focus problems that may have been attributable to the backs. Their intermittent focus problems were over. What did I do? I simply increased the pressure on the pressure plate by bonding another pressure plate spring to the original one. The pressure was then on a par with Bronica and Mamiya backs.

Any Hasselblad back can be "put to the pressure." Your repair technician can do what I do to help correct the intermittent focus problem by installing an additional plate spring, Hasselblad part number 13512. Be sure the springs are bonded. If you or your repair technician need further information, you may reach me through the bio information at the end of the article.

Does this resolve all back focus problems? No! There are several other factors involved, most of which are too technical to be enjoyed in this kind of article. Of those several factors, Bronica and Mamiya have incorporated most, but Hasselblad has yet to use effectively.

Now that you are armed with this information, study your images and if you suspect a focus problem with your backs, don't blame yourself. Take a close look at your backs and see if you can put your finger on the problem.

John Petterson is a medium-format repairman with Christian Photo, Des Moines, Iowa. He is a former professional photographer and studio co-owner, who has been involved in camera repair since 1960. To reach John, write, call, FAX or e-mail: Christian Photo, Attn: John Petterson, 6721 Douglas Ave., Des Moines, IA 50322 (515) 270-8048, fax (515) 270-8056; e-mail [email protected]

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