120 film in an RB67 ProS 220 back??

Discussion in 'Medium Format Cameras and Accessories' started by stradibarrius, Mar 22, 2009.

  1. stradibarrius

    stradibarrius Member

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    What will happen id I load 120 fim in an RB67 220 back? What is the reason it will not work? Does it have something to do with the fact that the 120 has the paper fot the entire length of the roll?
     
  2. BobNewYork

    BobNewYork Member

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    I have no experience of the RB, but the Bronica, (SQ-A at least) works fine with 120 in a 220 back. The only thing you have to do is cover the lens after the 12th shot then advance and fire a few times as you wind off the rear paper "leader". It's just a pain to keep checking the film counter so you know when you reach the last frame. If you don't you're last shots will be on backing paper - and those are always the best ones!!

    Bob H
     
  3. archphoto

    archphoto Member

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    I don't think it will give you much problems, just watch your frame-counter and finish the roll in complete darkness.

    Peter
     
  4. thisismyname09

    thisismyname09 Member

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    I've read that using 120 film in a 220 back will cause the image to be slightly out of focus because the thickness of 120 film is double that of 220, since 120 has a paper backing and 220 doesn't.
     
  5. stradibarrius

    stradibarrius Member

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    I don't think that is correct. The paper is on the back side and the film plane is still in the same position.
     
  6. BobNewYork

    BobNewYork Member

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    I've certainly noticed no focus problems using 120 film in a 220 back with the Bronica. I can certainly understand the issue from a theoretical perspective but I would have thought that the spring in the pressure plate forces the film evenly against the frame edge in the camera body and that with or without backing paper, the pressure plate can't force the film further forward than the frame edge - where it's supposed to be.

    Bob H
     
  7. EdColorado

    EdColorado Member

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    In all the many discussions I've read and taken part in on this subject none of the reasons to not use 120 in a 220 back have ever made much sense to me. As Bob H. said the addition of a paper back cant force the film into the body farther than the frame rails. Just isn't going to happen, the body is in the way. I've heard that the pressure plates of the two backs have differing amounts of force due to one being setup for a paper backing and the other not. We're talking a very minor difference in thickness which would warrant no or very small amounts of pressure change. If such a small difference mattered then our old backs wouldn't work anymore as the old springs have lost much of their original tension. I have been told that Mamiya said not to do it but I'd expect that, they want to sell everyone both backs, not just a bunch of 220s. Then there's the problem of tension on the mechanism as you pull the 120 film through a 220 back, increased strain due to the paper backing. From a manufacturing perspective it makes no sense. The slight difference in part design between the two backs would add huge costs to manufacture. If there is a difference between the two film types, then both backs would use the stronger part. I'm tempted to take a couple of these apart to see whats different between the two but I don't have any spares to sacrifice. Anyone have a broken insert to send me I'll rip em apart and document the differences. I doubt there are any other than those related to frame count.
     
  8. archphoto

    archphoto Member

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    Dear Stradibarrius, (and all others)

    There will be no film-flatness problem what so ever as the film will be presured to the guide rails period.
    Otherwise you would see a diference of sharpness between films as not all film emulsions are equaly thick.

    You can not adjust your frame counter as with the Rollei SL66, the Bronica and other backs that are 120/220 and there you will
    have a slight problem, that is all !

    Please try it out and let us know so all of us can leave this riddle behind us.

    Peter
     
  9. Andrew4x5

    Andrew4x5 Member

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    You may notice that it's harder to wind on the film because the space between the film rails and the pressure plate is designed for film-only, not film+backing paper. The backs of some brands, such as Bronica, may accommodate the extra thickness; but others may not be so tolerant.
     
  10. PHOTOTONE

    PHOTOTONE Member

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    You "may" have some issues with frame spacing. That is the only thing I can think of.
     
  11. paul ron

    paul ron Member

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    Just keep careful track of your frame count as you shoot so you don't go shooting on the tail leader with no film That's of course where your best shots will be lost.

    BTW 120 in a 220 back needs to start at a differnt point, not the arrow on the leader, closer to the start by a couple inches. So take a paper backing n run it thorough n adjust your start point for the first frame to fall in the right place just past eh tape holding the film on the backing paper. I generally wind on one turn on the empty spool n that gives me a perfect frame one start, otherwise you'll start late on the film n loose one or 2 frames on the tail.

    FYI.. the repair manual shows the only difference is in the frame counter parts not the rest of the operating parts in the 120 vs 220 backs... no springs n preasure plate differences, no focusing problems... all myth. Try, run the paper backing to test it n see for yourself.