120 film in 220 backs?

Discussion in 'Medium Format Cameras and Accessories' started by Colin Corneau, Sep 3, 2008.

  1. Colin Corneau

    Colin Corneau Subscriber

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    My humble little SQ-Ai came with 220 backs, which I've been putting 120 film through.

    Is this no problem, or can it damage the backs somehow?
     
  2. iamzip

    iamzip Member

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    the Manual for my *new* Mamiya M645J says this:
    "If the wrong insert is used, the correct film plane will not be maintained and optimum sharpness will not be acheived. Moreover, if 120 film is used in the 220 film insert, there is the danger of the leader paper getting caught in the shutter causing damage to the camera."

    Don't know how much of this applies to you.
     
  3. PhotoJim

    PhotoJim Member

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    You definitely won't get optimum sharpness. Some claim it doesn't matter, but it does. Cameras that can use either film in a given back (or don't take backs but take both types of film) have adjustable pressure plates that put 220 film slightly closer to the shutter. (The paper backing on 120 makes a noticeable difference in the quality of the focus.)

    KEH has decent, BGN-grade 120 backs for around $50-60. 220 backs are significantly cheaper because they were in high supply (pros loved them) and now are of limited utility (few films come in 120 - e.g. the only black and white emulsion you can get in 220 is TXP).

    If you shoot colour, most colour films are available in 220.
     
  4. Q.G.

    Q.G. Inactive

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    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. :wink:
     
  5. ricksplace

    ricksplace Member

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    My Pentacon Six can use 120 or 220 without a change in the pressure plate. Negs are always bleedingly sharp with those zeiss lenses, even wide open on either film. I just shot a bunch of 220 and every neg came out razor sharp. So, Q.G., I agree with what you say.
     
  6. Edwardv

    Edwardv Member

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    Best to purchase a 120 back for the Bronica AQ-Ai.
     
  7. Colin Corneau

    Colin Corneau Subscriber

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    I'm debating selling it and getting a Hassy 500 C/M, so I haven't pursued getting the 120 back just yet. FWIW, the negs out of it have been good and print well.
     
  8. j_landecker

    j_landecker Member

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    I compared the pressure plates of Bronica 120 and 220 backs - the 220 plate has a step of about 0.005" on the outer edges (parallel to the film direction), while the 120 plate is flat. On the part of the back that attaches to the camera are two sets of silver rails - the pressure plate bears against the outer rails, and the film runs over the inner ones. 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. So with a 120 insert, the film and paper sandwich are running between the pressure plate and rails with about 0.0025" play. Maybe this is why you can never get a sharp picture with a Bronica :surprised:

    With a 220 insert and film, then, the height of the step on the pressure plate takes up the space normally occupied by the backing paper - one reason you can use any insert in any back shell with Bronicas. I don't have any 220 film to measure, but I recall that it's a little thinner than 120 film - can anyone verify that? If true, it would mean that the play between plate and rails is even bigger than with 120 film, increasing the potential for focus error.

    I don't know why Bronica does this and I haven't investigated the situation with other camera brands, but I imagine it's to decrease the film advance resistance, perhaps to decrease the load and power consumption on motor drives.

    Getting to the original question (finally), running 120 film with a 220 insert would mean that the pressure plate is actually pressing the film/paper sandwich against the inner rails, which is why advancing the film will feel stiffer than normal. I don't think this will do any damage, but you can try filling the stepped area on the pressure plate with a strip of any smooth-surfaced tape which is 0.005" thick (about the same as a sheet of paper). Bronica backs use an idler roller to determine frame spacing, so you shouldn't have any problem there. Do watch out for the leader length, though - the position of the start marks may differ between 120 and 220. And don't forget to stop shooting after frame 12. :wink:

    Jim
     
  9. Colin Corneau

    Colin Corneau Subscriber

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    Like running out of gas in your car, you only have to do this once to learn!
     
  10. Uncle Goose

    Uncle Goose Member

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    Why would you sell it if it works OK?? A new (old) back (or even just the insert) will not cost you a lot of money and I find the Bronica system less cumbersome then the Hassy 500 line. And it looks more modern and cooler than the hassy. In terms of image quality I still have to see any difference.

    I wouldn't advice using 120 in a 220 back as the pressure plate is different.
     
  11. ic-racer

    ic-racer Member

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    ??

    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.
     
  12. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    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.
     
  13. Q.G.

    Q.G. Inactive

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    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.

    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.
     
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  15. ic-racer

    ic-racer Member

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    I have a "Samoca 35" with a 'scratcher-plate' that behaves like that, but it is by no means a professional camera.
     
  16. Q.G.

    Q.G. Inactive

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    I have a load of Hasselblad backs that are like that too.
    But maybe that also by no means qualifies as professional equipment? :wink:

    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.
     
  17. ic-racer

    ic-racer Member

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    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 a moderator: Sep 6, 2008
  18. Q.G.

    Q.G. Inactive

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    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. :wink:
     
  19. ic-racer

    ic-racer Member

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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.
     
  20. Edwardv

    Edwardv Member

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  21. Edwardv

    Edwardv Member

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  22. Colin Corneau

    Colin Corneau Subscriber

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    Thank you for the link, Edwardv -- a question for you or anyone:

    Is there a difference, for my humble little SQ-Ai, between a 120-I, 120, and 120-B back?
     
  23. DWThomas

    DWThomas Subscriber

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    Not sure I can spell out exact differences, but I believe the I is the only one that interacts with the autoexposure stuff.

    I only have an SQ-A so it hasn't mattered here.

    DaveT
     
  24. Edwardv

    Edwardv Member

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    I would go with all Ai magazines for my camera. It has the locking dark slide which is very nice to have. The older magazines don't have this feature and can be be very disastrous it you pull accidentally or gets caught on something and the dark side is pulled out. Best to get the Ai and buy additional Ai dark sides with the lock for all Ai magazine. And DWThomas is correct that the AEIII meter is the choice for the Ai magazines.

    Good luck
     
  25. Robert Kerwin

    Robert Kerwin Member

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    The 120-I has the film speed dial on it and it electronically interfaces with a metered finder (such as the AE). If you only use a waistlevel or other non-metered finder, you don't need the 120-I, but it won't hurt anything if you use it. The plain 120 back has no electronic film speed interface. Other than that, there's no real difference between the two.

    The 120-B I thought was for the SQ-B series, not the SQ-A, but I could be wrong.
     
  26. DWThomas

    DWThomas Subscriber

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    Again, I don't own one, but I think it fits everything, but like the B body, it has no wires. My understanding is the SQ-B was supposed to have been a stripped down low cost manual exposure student model kit to offset the significant price of the SQ-Ai.

    Sorry about all the weasel-y qualifiers, but it's been a while since I researched the stuff and I only do the SQ-A.

    DaveT