[rollei_list] Re: 220 vs 120 film flatness
- From: Emmanuel Bigler <Emmanuel.Bigler@xxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Fri, 30 Apr 2010 20:27:26 +0200
CarlosMFreaza a écrit :
Carl Zeiss did a research about the film flatness using 220 and 120 film:
http://tinyurl.com/35kmksu
http://www.zeiss.de/C12567A8003B58B9/ContentsWWWIntern/134AEE504E89CD50C12569620039712C
Carlos ! And you could survive for 10 years without using 220 rollfilm,
since apparently you missed this article by Zeiss dated year 2000 ? ;-);-)
The problem apparently came with some fast lenses, in the style of f/2
designed for the Contax 645 camera.
With our beloved Rollei TLR stopped down to their best aperture, f/8 or
f/11, you can sleep quietly : the allowed depth-of-focus is plus or
minus 8 to 11 times yout favourite circle of least confusion ; I know
that you use something like 25 microns to compute your depth-of-field
tables, in order to get images in 6x6 that are top-class, it means that
you can allow flatness defects of about plus or minus 200 to 300 microns.
If the flatness problem was really an issue, Chris Perez could never
find on-film resolutions close to 100 cy/mm with a good old 120 rollfilm
on either a Rollei TLR or an Hasselblad with a 120 film back...
http://www.hevanet.com/cperez/test/fourcameras.html
It means that the actual sharpness available with a well-tued Rollei TLR
at f/8 is above 90 cy/mm, i.e. you could even choose a circle of least
confusion of about 10 microns for you depth-of-field tables !
Moreover as far as the Rollei TLR is concerned, correct me if I'm wrong
but I think that there is no special position of the film pressure plate
for 220 rollfilm ; it means that without its backing paper, 220 film is
"floating" between the plate and the film gate, with a spacing designed
for 120 (film + paper) thinckness... except for Rolleis with the glass
pressure plate. (this is anotther story..)
all the best !
--
Emmanuel
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