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From: askcmraguy@aol.com (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 askcmraguy@aol.com
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