Re: MF Projection in Mesa?

[Brian Reynolds <reynolds@xxxxxxxxx>]

George Themelis wrote:
> What advantages will MF projection have, considering that the
> size of the screen will not change?
> 

This question is similar to those often asked in the various
rec.photo.equipment.* newsgroups regarding 35mm vs. MF vs. LF
cameras.  The advantages of moving up in format size are twofold.

First, assuming that all the final images are printed (or projected)
to the same size (using enlargers or projectors of the same quality),
the final image from the larger format (either MF or LF) will have
more detail than the smaller format (either 35mm or MF).

At this point the 35mm advocates normally mention that 35mm lenses
have much higher resolving power than the lenses for larger formats.
What they overlook is that the difference in resolving power between
35mm lenses and Medium or Large Format lenses of the same vintage is
less than the difference in the magnification factors needed to
produce the same final image size from the various formats.

For example, in order to produce an 8x10 final image a 35mm frame is
magnified about 8X (to produce an 8x12 cropped to 8x10), a 6x6 MF
frame 4.5X (to produce a 10x10 cropped to 8x10), a 6x9 frame (same
aspect ratio as 35mm) 3.6X (to produce an 8x12 cropped to 8x10), a 4x5
film 2X, and an 8x10 film can be contact printed (1X).  Assuming a
really bad 8x10 lens has an on film resolving power of 30 line pairs
per inch (lppi) the 35mm lens would have to have an on film resolving
power of more than 240lppi to better the contact printed 8x10 image.
Extraordinary 35mm lenses have occasionally been tested at about
90lppi.  A 30lppi 8x10 lens could produce a 21x26 final image that
would have the same level of detail as an 8x10 from a 90lppi 35mm
lens.  An 8x10 lens would have to resolve less than 12lppi on film to
appear worse (in a contact print) than an extraordinary 35mm lens.  In
fact modern 35mm, MF and LF lenses actually all have about the same
resolving power on film.  Some 1950's era LF lenses (Kodak Ektars and
Commercial Ektars) perform about as good as modern lenses.  (See Kerry
Thalmann's and Chris Perez's lens testing page
<URL:http://www.hevanet.com/cperez/testing.html> for a comparison of
various lenses for different formats from different vintages.  Chris
has put a lot of interesting information about lens testing and
comparisons on his page.)

Second, the tonality (rate of change of the tone between areas of
different tones) of a larger format will be better (smoother) than the
smaller format.  I'm not exactly sure how this works, but here is my
understanding of it.  If you set up the same composition in two
different formats (e.g., 35mm and 6x9 MF) the transitions in tone
(e.g., from midtone to shadows) in the larger format will have more
area on the film to make the same transition.  This means that there
are more grains in the transition area and therefore there can be a
smoother transition from one tone to the next.

As an example, assume that there are only 2 grains per mm on film
(obviously too low given the above resolution examples, but it makes
the math easy).  If a scene is composed such that a smooth transition
from black to white occurs within 1mm on the 35mm frame then the tonal
transition on film will be from a black grain to a white grain.  On
the 6x9 frame there will be about 5 grains (1mm on 35mm film * 2.33
size factor between 35mm and 6x9 * 2grains/mm = 4.66 grains) in the
same transition.  The transition will have a black grain, two or three
grains of various greys, and a white grain.

Note that in the above examples I have chosen my numbers (by rounding,
etc.) to favor 35mm.

As far as actual experience in these differences one example I can
think of is the difference between 16mm or 35mm movie projection and
IMAX or other large format movie projection.  There are problems with
this since the larger formats are usually shown on larger screens.  At
SIGGRAPH (and I assume other conferences) various formats are often
projected on the same screen (although they will move some of the side
curtains) and the differences are readily apparent.

-- 
Brian Reynolds                  | "Dee Dee!  Don't touch that button!"
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http://www.panix.com/~reynolds  |    -- Dexter and Dee Dee
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