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  1. #11
    ic-racer's Avatar
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    Quote Originally Posted by Q.G. View Post
    The pressure plate just puts pressure on the film. It's the thing it is pushing the film against that determines film position, and focus.

    The film + paper combination of 120 film is, of course, thicker than a film alone.
    So what 'adjustable' entails in cameras with adjustable pressure plates, is either moving the pressure plate back to allow the thicker 120 film to pass between it and the image frame without too much strain, or(/and) an increase of pressure, which however would only be needed if the plate exerts just enough pressure to push the thicker 120 combo against the picture frame, but not enough to push the 220 film against it as well.
    For as long as it indeed exerts enough pressure, the film will be pushed into the right position, the images will be sharp, no matter how thick the film. The plate being sprung, i can't really imagine that the pressure is (nor needs to be) so finely tuned to need two separate positions for 120 and 220 film.

    What however also needs to be done when changing film type, is switch between two modes of the frame counter/frame spacing mechanism. So it may very well be that this is all the 'adjustable' pressure plate does: act as a switch for the counter/spacing mechanism.

    If so: it really does not matter.
    ??

    Except for what is noted below, pressure plates push against (exert their pressure on) the outer pair of film rails only. The film rides in the groove formed by the pressure plate and the inner rails. Adjustable pressure plates for 220/120 alter the width of the groove the film rides in, keeping the emulsion surface the same distance from the lens in either case. The emulsion rides on the inner film rails (which are fixed with respect to the lens) in both 220 and 120 film. The adjustable pressure plate opens up the back of the channel a little to allow for the thicker 120 film/paper combo.

    Pressure plates that actually PRESS on the film are found in MINOX and MINOLTA 16mm cameras (perhaps others). These special pressure plates have a mechanism to RELEASE the plate when the film is advanced and subsequently only require one set of film rails.

  2. #12
    David A. Goldfarb's Avatar
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    Quote Originally Posted by j_landecker View Post
    I measure a height difference of 0.012" between the outer and inner rails. I just measured a couple of different films, and the film on both is 0.005" thick and the backing paper 0.0045" thick.
    I looked into the thickness of films and backings when I was having frame spacing issues with a Linhof Rollex back that were due to differences between the thickness of modern films and backings compared to the 120 films that were made when the back was new. In general, 120 and 220 films of the same type are the same thickness, but they aren't all necessarily the same for all the films made by a certain brand. There was a period, for example, when T-Max MF films were made on a thicker base than other films, and this caused problems with some cameras. Backing papers are not the same thickness from one brand to the next. Ilford films use thicker backing paper than Fuji, for instance.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
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  3. #13

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    Quote Originally Posted by ic-racer View Post
    Except for what is noted below, pressure plates push against (exert their pressure on) the outer pair of film rails only. The film rides in the groove formed by the pressure plate and the inner rails.
    For some brands/types this may indeed be true. But by no means for all.
    And the ones that do press against the film, to put it into position, do not need (nor have) a mechanism to release pressure during transport. Really not necessary.

    And i might add that it is the better solution to not just form a channel for the film to slip through (i.e. allow it room to also move out of the plane of focus, by no matter how little), but actually press it into position.

    Quote Originally Posted by ic-racer View Post
    Adjustable pressure plates for 220/120 alter the width of the groove the film rides in, keeping the emulsion surface the same distance from the lens in either case. The emulsion rides on the inner film rails (which are fixed with respect to the lens) in both 220 and 120 film. The adjustable pressure plate opens up the back of the channel a little to allow for the thicker 120 film/paper combo.
    Which would make you wonder what the outer pair of rails the pressure plate would push against are for, if it is also o.k. to move the plate away from there.

  4. #14
    ic-racer's Avatar
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    Quote Originally Posted by Q.G. View Post
    For some brands/types this may indeed be true. But by no means for all.
    And the ones that do press against the film, to put it into position, do not need (nor have) a mechanism to release pressure during transport. Really not necessary.
    I have a "Samoca 35" with a 'scratcher-plate' that behaves like that, but it is by no means a professional camera.

  5. #15

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    Quote Originally Posted by ic-racer View Post
    I have a "Samoca 35" with a 'scratcher-plate' that behaves like that, but it is by no means a professional camera.
    I have a load of Hasselblad backs that are like that too.
    But maybe that also by no means qualifies as professional equipment?

    But think about it: the film channel solution is only restricting the film to be within the width of the channel.
    The pressure plate solution actively puts the film where it needs to be.

    And "scratcher plate"?
    I certainly never had a scratch. Never heard of any other HB-user who had either.

  6. #16
    ic-racer's Avatar
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    Quote Originally Posted by Q.G. View Post
    I have a load of Hasselblad backs that are like that too.
    But maybe that also by no means qualifies as professional equipment?

    But think about it: the film channel solution is only restricting the film to be within the width of the channel.
    The pressure plate solution actively puts the film where it needs to be.

    And "scratcher plate"?
    I certainly never had a scratch. Never heard of any other HB-user who had either.
    That Samoca has no rollers like the Hassy, so I agree with you that it does not compare. The Hassy/Keiv method is somewhat of an enigma, though (I can't think of any other like it). Koni-omega system is more like the Minox, with pressure on the plate released for film transport.
    Last edited by ic-racer; 09-06-2008 at 04:55 PM. Click to view previous post history.

  7. #17

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    Quote Originally Posted by ic-racer View Post
    The Hassy/Keiv method is somewhat of an enigma
    It needn't be. All the pressure plate needs to do is to push the film against the picture frame.
    Film isn't putting up a fight resisting, so there is no need for great force.
    So there's no need either for a releasing mechanism: the pressure that suffices to push the film in position (and not just form a channel for film to move through, and in) is slight enough not to cause any problem during transport. No great force needed. No scratches to be feared.

    The same method (pushing film against edges that set/define the film plane) is used in the Hasselblad photogrammetric cameras.
    And there again it doesn't matter how thick the film stock is that is used: it will always be in the correct position, without a need to adjust pressure plates.

    So if there is an enigma, it is why the film-channel method (and the adjustable 'pressure' plate) and/or the release-for-transport method exist.

  8. #18
    ic-racer's Avatar
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    Just as a curious note with features of both we were discussing. The Rollei 3000 series cameras also had a set of rollers (which contact the emulsion surface), similar to the Hassy system (the film takes a 'reverse curve' like the Hassy), but with the more conventional pressure plate and two sets of film rails.

  9. #19

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    Visit KEH for Bronica 120/222 magazines. For some reason they are more expensive than the 645 120/220 magazines.

    http://www.keh.com/OnLineStore/Produ...BCL=&GBC=&GCC=

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