Ok, get ready for minor rant...
How dare these morons try to convince you that the laws of physics do not
apply to cameras. There is no way that the "end result" image of a 35mm
neg is going to be as good as a medium format image. When producing the
final print you are magnifying not only the grain but also any resolution
problems of the camera lens. You can control the grain through film
selection, but lens resolution will always be the limiting factor. Let's
compare factors here:
A. In 35mm film, the "normal" lens is 50mm. In 6x6 or 645 film, the normal
lens is 80mm. This will produce the same image size in relation to the
overall usable film area. (For instance a subject that occupies 500f the
35mm frame also occupies 500f the medium format frame). If my
calculations are correct, a 645 frame has 2.5x more "pixels" or film grains
holding the subject image than 35mm film. I would say that given equal
films in both film formats will result in a potentially sharper image from
the larger film format.
B. Every lens has a maximum resolution that occurs usually around the
middle F-stops. This is a trade-off between DOF and diffraction. The 80mm
lens will potentially produce more diffraction than a 50mm lens given the
same DOF in the resulting film images. In other words, for a 80mm lens to
have a DOF of 20feet to infinity requires at least one more stop than a
50mm lens. However, medium format lenses are designed for maximum
sharpness at a stopped down (usually around F11-16) setting whereas 35mm
camera lenses are designed for maximum sharpness from nearly wide open
(Nikon) to around F8 (Olympus, Canon). Given that lens designs are
optimized for the format, the resolution, corrected for DOF, is nearly
identical between medium format and 35mm.
C. However, if the 80mm lens is able to produce 100 lpm and so is the 50mm
lens then everything is equal. Right? Wrong! It comes down the
magnification of the negative or tranny at that point. If I need to
magnify the 35mm frame 2.5x more than the medium format frame then the
medium format frame will end up being sharper.
Again, it all comes down to physics.
Ok, now on the subject of manual focus vs auto focus.
AF's inability to accurately nail the focus 1000f the time is a
misleading gripe. Although, it is possible to outfocus AF when you really
try, you must remember that it wont be wrong or out 1000f the time. In
your testing of AF's repeatability you will see that it lands pretty close
but won't exactly match the distance setting time after time. However, DOF
usually is enough to cover any slop and when it doesn't the law of averages
comes into play. The chances of the focus always landing on the extreme
outside limits of acceptable focus are far less than those that leand near
the middle of the window. This varies from camera make/model, of course,
and I've been extremely pleased with my IS-3, buy have had miserable
results with Canon A2 cameras. Nikon F5/F100 cameras and the new lenses
are very fast and accurate.
Ken Norton
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