Yashica 24 -- convert to 120?

[itsdoable]

Pressure plate holds film against film gate runners....
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All the 120 in 220 talk and worries is about motorized backs and fear of burning the motor due to somewhat higher friction, most of which is unsubstantiated and mostly only theoretically true.....

There are a few differences between 120 and 220 that need to be taken into account, when suing 120 film in a 220 camera/back.

1) different # of frames

- which is not a problem with using 120 on a 220 camera/back, but even early Hasselblads had a way to use 220 film in a 120 back by sealing the window and resetting the counter at frame 12.​

3) different length leader

- resulting in the start of the 1st frame being too soon, and losing the 1st frame. This can be compensated for if you know the lengths, or in the case of the Yashica 24, which had start marks for both types of films.
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2) thinner medium with no backing paper

- if your frame counter use a red window, it would expose the film.
- if your frame counter used rotation of the take-up spool, then frame spacing would increase towards the end of the roll, resulting in the potential to lose the last frame
- more pressure on the film rails as the gap for 220 was smaller than the 120 medium. Conversely, if you had 220 in a 120 back, the gap may be bigger than the medium, resulting in out focus issues.
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The last issue is a bit more complex. Early folders did not have a gap, the film was pressed against he rails. This would sometimes cause the film to bulge when it expanded with temperature, as the edges were held firm, and the polyester film base expanded more than the metal bodies. This was sometimes blamed on miss-focusing, or that pulling the bellows out caused the film to bulge. This was addressed buy using the double rails you see in all modern film cameras, which use the outer rails to channel the film and hold the pressure plate so there is a gap for the film to travel on the inner rails. This also lowered the resistance to advance the film, which gave the wind a better feel, and improved winder/motor drive performance.

The only real issue is film bulge, which does not happen that often, and can be remedied by adding a layer of tape to the spot on the pressure plate that sits on the outer rails. As long as #1 and #2 are addressed.

I have no issues using 220 backs/inserts with 120 film when the above are accounted for - but I usually have a 120 back available, so I don't do this that often.