Let us start with the assumption that we shoot multiple formats, and regardless of aspect ratio our end goal is to produce a 32" x 40" print (for discussion purposes)
In order to do so, we start...
- with 93x120mm sheetfilm neg and crop to fit the 4:5 aspect ratio print...enlarge image by 10.9X
- with 56x68mm 6x7 neg and crop to fit the 4:5 aspect ratio print...enlarge image by 14.9X
- with 56x56mm 6x6 neg and crop to fit the 4:5 aspect ratio print...enlarge image by 18.9X
- with 43x56mm 645 neg and crop to fit the 4:5 aspect ratio print...enlarge image by 18.1X
- with 24x36mm 135 format neg and crop to fit the 4:5 aspect ratio print...enlarge the image by 33.9X
That is the REAL advantage that would be achieved in the same final print, from the apparent size differences!!!
The result is -- if we first assume the same line-pairs per millimeter of
on-print detail resoluton can be delivered from the lenses of all formats!
Unfortunately we seldom/never see MTF tobjective numbers of testing of different format lenses all done by a single test agency...we only see tests by different agencies and we (wrongly) assume one can directly compare results and get truly valid comparisons.
We know, from past discussions in photography magazines about print sharpness that when the final print has 5 line-pairs per on-print-millimeter our eyes and brains perceive the print as 'sharp' (an eagle might know better, but our limited human eye+brain is fooled at that minimum! So
- the 4x5 format lens has to deliver 95 lines per millimeter to the negative
- the 6x7 format lens has to deliver 91 lines per millimeter to the negative
- the 6x6 format lens has to deliver 75 lines per millimeter to the negative
- the 645 format lens has to deliver 55 lines per millimeter to the negative
- the 135 format lens has to deliver 169 lines per millimeter to the negative
So we have to ask ourselves if each of the lenses can indeed meet such high standards. The specific lens MATTERS in whether or not a certain format is 'better'!
Lastly we assume that the same film is shot in all five of the different format cameras, and (assuming the lens is up to it an all cases) we can judge finally by the criteria of the higher/lower enlargement factor in the apparent visibility of grain when all five prints are viewed from the same distance,
the 4x5 grain is the standard against which we judge other prints, as it is magnified by the least amount.
- the 6x7 grain is 1.37X more apparent in size (single direction) or 1.9X larger (in area)
- the 6x6 grain is 1.66X more apparent in size (single direction) or 2.75X larger (in area)
- the 645 grain is 1.73X more apparent in size (single direction) or 3X larger (in area)
- the 135 grain is 3.1X more apparent in size (single direction) or 9.6X larger (in area)