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12-27-2010, 03:45 PM   #1
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Interesting footnote re roll film flatness

QuoteQuote:
In sequence of introduction the Kodak Ektra camera followed Kodak's Medalist 620 camera, which had been an exercise in film flatness -
footnote: Most of the basic research in film flatness was done for this camera because of problems encountered in trying to build a folding camera with an f/3.5 lens. The problem rested in the fact that roll film was designed to overcome the curl of the roll by a slight tendency to curl with the edges inward (toward the lens). At large lens openings, the curling made the edges unsharp; the same problem was true with press cameras, which were generally unsharp at large openings because the sheet film was not completely flat in the holder and even less so in film packs. The resulting design of the Kodak Medalist camera gave the film a two-way curl, thus overcoming the problem. The Medalist was one of the sharpest picture takers ever produced by Kodak and introduced the concept of interchangeable backs, at least to the extent of allowing a ground-glass back to be substituted for the regular back, and a cut-film holder to be used in place of roll film. While the idea was not new, most cameras, such as the Kodak Recomar, used the opposite approach. Kodak had never before produced a roll film attachment for a plate camera
- p. 218, Glass, Brass, & Chrome, The American 35mm Miniature Camera, by Kalton C. Lahue and Joseph A. Bailey, University of Oklahoma Press, 1972

This was intriguing relative to the P645 120 and 220 inserts - why the 220 might not give optimum sharpness when modified to handle 120 film. Seems like the pressure plate etc does more than simply holds the film to the gate rails, there's some compensating curling going on. Maybe. Perhaps. At any rate, just looking at a Medalist I wouldn't have guessed.

12-28-2010, 03:32 AM   #2
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QuoteOriginally posted by Nesster Quote
- p. 218, Glass, Brass, & Chrome, The American 35mm Miniature Camera, by Kalton C. Lahue and Joseph A. Bailey, University of Oklahoma Press, 1972

This was intriguing relative to the P645 120 and 220 inserts - why the 220 might not give optimum sharpness when modified to handle 120 film. Seems like the pressure plate etc does more than simply holds the film to the gate rails, there's some compensating curling going on. Maybe. Perhaps. At any rate, just looking at a Medalist I wouldn't have guessed.

Interesting. This would suggest that the Medalist film transport might be best left alone and not converted to 120?

Cheers,

Luc
12-28-2010, 05:23 PM   #3
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That is certainly interesting—and somewhat alarming. I have not tested the modified P645 220 inserts against the 120 ones. But I do not see any change, quite frankly, between them, certainly not in terms of curling, so my guess is that this is relevant for Medalist only, not Pentax 645. But correct me when I'm wrong.
12-28-2010, 05:42 PM   #4
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Smolk, I'm encouraged by your comment - I didn't see any reason why the 220 insert wouldn't be as sharp as the 120 though the one time I tried it I also was trying a close up filter... and I've seen comments about the 220 being unsharp with 120 film. I haven't tried it again myself.

The way the insert feeds the film in a reverse sort of way I think addresses any of the curling issues with the P645.

I'm also wondering if the flatness issue is what kept e.g. TLRs and most folders at or above f/3.5 for all those years.


I have film in my 124G but once that's out I'll examine with care what the pressure plate does differently (if anything) when switching it from 120 to 220

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