Koni-Omega Rapid: Can I put 220 in a 120 back?

hsandler · Jul 3, 2018

What will happen? I have a fair bit of expired 220 film to use up, but not willing to invest in a 220 back for my Rapid. As I understand it, the film advance mechanism winds progressively fewer turns as the film advances based on the anticipated diameter of the take up spool as film winds onto it. So without the backing paper, I might expect some frame overlap in the early frames and then too much frame spacing towards the end (once I advance past 10, I think it winds the maximum amount per action until it again reaches 1). I realize the frame counter will stop at 10 and then begin showing the dots leading to the "load" setting and then back to "1'. If I continue advancing, I expect I might get 17 or so frames out of a roll. Has anyone ever tried it?

Dismayed · Jul 3, 2018

There's a 220 back on eBay right now for a BIN of $10. Best to buy the back - and tp have flat film when you shoot.

hsandler · Jul 3, 2018

Dismayed said:
There's a 220 back on eBay right now for a BIN of $10. Best to buy the back - and tp have flat film when you shoot.

Could you pm me the link? I don't see it. Note that the KO Rapid uses different backs than the later Rapid Omega M, 100 and 200 models which had dark slides. There are no mid roll changes with the KO Rapid.

Dismayed · Jul 3, 2018

hsandler said:
Could you pm me the link? I don't see it. Note that the KO Rapid uses different backs than the later Rapid Omega M, 100 and 200 models which had dark slides. There are no mid roll changes with the KO Rapid.

Sorry, it was a back form a Koni Omega. I would worry about film flatness using the 120 back. Perhaps you could create a shim with an index card. to compensate for the missing backing paper. No idea how it would work, but a test using a single roll may be illuminating.

Or you could sell the 220 film and shoot 120.

fjpod · Jul 3, 2018

220 backs are dirt cheap. Check on youtube or other photo sites. Often there is really no difference.

darkroommike · Jul 7, 2018

The Omega backs count exposures, a 120 back is ten and done and then will crank off until it thinks it has reached the end of the roll and lock. Get a 220 back. Probably for less money than you could get for a roll of 220 film!

hsandler · Jul 7, 2018

Update: So I tried it and it worked much as I expected. I got 19 exposures on a roll of 220. I just kept cranking after frame 10 (have to push the advance unlock at frame 10 to continue). Frame spacing started off OK, frames from about 6-9 were bunched together, but did not actually overlap by more than a mm (anyway, I had this happen on regular 120 film too), and frames toward the end had too much spacing. However, my 120 back appears to have a light leak near the hinge or closure, so I got some frames with slit-like leak lines, which I don't get on 120 film because the backing paper protects it.

shutterfinger · Jul 7, 2018

Film spacing issues result from the holder needing a CLA and modern films being thinner than the era the back was made/designed in.
Two types of drive systems are used in film holders, gear driven, and clutch systems. Film thickness is 4.5 mil (.0045 inch) for Kodak and Ilford, 3.5 mil (.0035 inch) for Fuji, and 3mil (.003 inch) for Foma.
Film thickness spacing problems can be resolved by increasing the diameter of the take up roller (not pin roller), if used, by .008 to .012 inch (double or triple layer of backing paper bonded to the roller) and similar to the center of the take up spool on holders that do not use a roller system.

darkroommike · Jul 9, 2018

shutterfinger said:
Film spacing issues result from the holder needing a CLA and modern films being thinner than the era the back was made/designed in.
Two types of drive systems are used in film holders, gear driven, and clutch systems. Film thickness is 4.5 mil (.0045 inch) for Kodak and Ilford, 3.5 mil (.0035 inch) for Fuji, and 3mil (.003 inch) for Foma.
Film thickness spacing problems can be resolved by increasing the diameter of the take up roller (not pin roller), if used, by .008 to .012 inch (double or triple layer of backing paper bonded to the roller) and similar to the center of the take up spool on holders that do not use a roller system.

220 in a Rapid Omega 120 holder accounts for the spacing issue in this case, the other problem I have had with my Rapid is getting only 9 shoots when using Shanghai film since the paper backing is so thick.

Koni-Omega Rapid: Can I put 220 in a 120 back?

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