Re: Print Quality from M6 vs. Medium Format

[pgs@thillana.lcs.mit.edu (Patrick Sobalvarro)]

   From: Jim Brick <jim@brick.org>
   Date: Wed, 06 Aug 1997 16:47:58 -0700

   No. At least nine times more information in a MF image vs 35mm
   image.

Jim, I think you made a mistake in this calculation.  Even if you are
concerned mostly about total information content (which scales with
image area), a medium format image has an area of 60mm x 70mm = 4200
mm^2, and a 35mm image has an area of 24mm x 36mm = 864 mm^2.  The
ratio here is 4200/864 = 4.86, which isn't 9.

But most people who examine how humans perceive sharpness report that
sharpness is perceived as a linear measure, not a quadratic one.  That
is, humans do not evaluate the sharpness of an image based on its
total information content, but on their ability to distinguish two
features that are next to each other.  This is why resolution is
typically measured in line pairs/mm.  On this basis, to get an 8x10
image, a 6x7 negative must be enlarged about 3.4 times and a 35mm
negative must be enlarged about 8 times -- that is, the difference is
about a factor of 2.4.

A good book on this topic is "Image Clarity: High-Resolution
Photography" by John B. Williams, published by Focal Press.  The
author makes the point that with good technique and equipment and
emulsions, it is possible to get results with 35mm equipment that most
people would have believed only possible in larger formats.

Of course, just as you say, good MF is just better than good 35mm, and
it's pointless to pretend otherwise.  A factor of 2.4 is a really big
factor -- everything else being equal, a 16x20 made with 6x7 film will
look sharper than an 8x10 made with 35mm film.

- -Patrick