120 film in 220 backs?
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?
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.
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.
Jim MacKenzie - Regina, Saskatchewan, Canada
A bunch of Nikons; Feds, Zorkis and a Kiev; Pentax 67-II (inherited from my deceased father-in-law); Bronica SQ-A; and a nice Shen Hao 4x5 field camera with 3 decent lenses that needs to be taken outside more. Oh, and as of mid-2012, one of those bodies we don't talk about here.
Favourite film: do I need to pick only one?
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.
Originally Posted by PhotoJim
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.
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.
"I'm still developing"
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Best to purchase a 120 back for the Bronica AQ-Ai.
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.
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 :o
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.
Like running out of gas in your car, you only have to do this once to learn!
And don't forget to stop shooting after frame 12.
Originally Posted by Colin Corneau
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.
Sure, I could give you a boring explanation who I really am but I rather let the Origami do the talking.