Jim wrote:
> Never heard of that problem. Never realized it is a problem.
It has been a constant hassle on my 645n and it seems unsolvable. I've tried different
backs but the problem remains to a variable degree. If you search the medium format
section of Photo.net for "film flatness" you will see thats its common on medium
format and particularly for the 645 systems. It is because of the bending of the film
these system provides. Its seems like common wisdom says that film shouldn't stay more
than 5min still in the camera before the film "memorize" the bend and won't lay flat.
Anyway, Carl Zeiss have analyzed the problem and claim that 220 film is musch better,
by a factor of 2, in holding the film flat. So my last resort is to buy a 220 magazine
and see if the problem dissapear. Strangely, Zeiss people say that the problem is
largest with wide angles although I can't see why; one should expect it to be wrose
with telephotos due to their smaller DOF or..? I have, however, experienced that the
problems is indeed worse with the 45mm; only once have I seen it with the 120mm. The
45mm has puzzled me becasue I couldn't really say whether it was a dog or not; some
images seem fuzzy while others seem sharp. Maybe its due to film flatness.
Anyway the film flatness issue is seen by the fact that parts of the images is out of
fucus. In my case usually the lower half.
Below is a post made on the issue on Photo.net:
--------------------------------------------------------------------
The problem is real! This is what I wrote about it in Zeiss Camera Lens News (you can
access CLN at www.zeiss.de, select English language):
Is rollfilm 220 better than 120 in terms of film flatness?
Zeiss has recently developed a new measuring system to evaluate film flatness in
medium format photography.
The new system is based on an computerized microscope that can automatically scan and
focus on multiple points of a film frame in a medium format camera magazine. The
obtained focusing data are recorded by a computer and evaluated by a propriatory Zeiss
software. The result is a mapping of the film topography with an accuracy of one
millionth of a meter (1 micron), according to the developer of this system.
The purpose of this new device is to find out how well film magazine mechanics are
designed in today's medium format camera systems, how precise they position the film
and how well they hold it flat. From these findings Zeiss can draw conclusions about
the field flatness required for medium format lenses and Zeiss can also trace causes
for lack of sharpness in customer's photos. This is particularly interesting since
more than 99% of all customer complaints about lacking sharpness in their photos can
be attributed to misalignments of critical components in camera, viewfinder, or
magazine, focus errors, camera shake and vibrations, film curvature, and other
reasons.
So far, Zeiss has found that film curvature can have a major influence as a source of
unsharpness. This has also been known by Zeiss' camera making partners Alpa,
Hasselblad, Kyocera (Contax) and Rollei. Since Zeiss' evaluation program is not
completed yet, we would like not to draw too many conclusions prematurely. But two
things can be stated already as hints to enable sharper photos with medium format
cameras at wide open apertures, since exactly those are invited by the high level of
aberration correction in Zeiss lenses:
1. 220 type rollfilm usually offers better flatness than 120 type by a factor of
almost 2. This is an advantage with fast, motorized cameras like the Contax 645 AF,
Hasselblad 555 ELD (and previous motorized Hasselblad cameras) and Rolleiflex 6000
series cameras.
2. Film flatness problems are mainly caused by the combined influence of two factors:
the rollers in the camera or magazine that bend the film, and the time a certain part
of the film is bent by such a roller.
Camera manufacturers usually space the rollers in a way that bent portions of the film
will never be positioned near the center of the image. Therefore only marginal regions
of the image should be affected by sharpness problems due to film flatness errors.
Since the photographer cannot alter the geometry and mechanics of his camera, he can
only influence the other factor: time. A film run through the camera without much time
between exposures should result in good flatness and hence sharpness. Five minutes
between exposures may be some sort of limit, depending on brand and type of film. 15
minutes are likely to show an influence of bending around rollers. Two hours
definitively will.
As a rule of thumb: For best sharpness in medium format, prefer 220 type roll film and
run it through the camera rather quickly.
Camera Lens News No. 10, Summer 2000 [Quit]
-- Kornelius J. Fleischer, March 08, 2001; 03:21 A.M. Eastern
It is a problem not only at wide open apertures. There, it can easily ruin your
picture. But even with stopped down lenses, say f/11 or f/16 you may experience focus
shifts that you cannot tolerate. This problem has more impact with wide angle lenses
than longer focal lengths. Of course, it is worst wide open. The medium format film
magazine that we found gives the best film flatness is the rather new 4560 reversible
magazine for Rollei 6000. We also found why and how the new Mamiya 645 AF magazine
produces the sharpness problems discussed elsewhere in this forum recently.
-- Kornelius J. Fleischer, March 09, 2001; 03:34 A.M. Eastern
-
This message is from the Pentax-Discuss Mail List. To unsubscribe,
go to http://www.pdml.net and follow the directions. Don't forget to
visit the Pentax Users' Gallery at http://pug.komkon.org .
