P645 Insert - Difference between 120 and 220

Ian Grant · May 30, 2018

MattKing said:
FWIW, when Mamiya used to maintain their own film camera forum, it included advice from Mamiya USA that 120 film could be used in 220 inserts, but the extra thickness of the film would contribute to premature wear of the springs in the inserts.
IIRC, this was in reference to the 645 inserts.

I never bought a 220 film insert for my Mamiya 645 1000S and J, so was rather surprised to find I was using one with 120 film, I did loan my 645J to a friend for about a year so maybe she added the 220 insert.

The major issue is the extra thickness which you've rightly high lighted Matt wil weaken the pressure plate springs.

Ian

Sirius Glass · May 30, 2018

Billy Axeman said:
When you are buying a magazine (insert) be sure it comes with the holder. It prevents scratching the transport rolls and the pressure plate during transport. It also has a rubber seal in the edge to keep dust out and it makes the unit light tight. In this way you can take several preloaded magazines with you for a quick swap.

I do not know about Pentax but the Hasselblad magazine will register at the start and think that the arrow is aligned with the mark. Thus the film will need to be advanced and several frames lost. Buy another film back and switch film mid roll.

Billy Axeman · May 30, 2018

Sirius Glass said:
I do not know about Pentax but the Hasselblad magazine will register at the start and think that the arrow is aligned with the mark. Thus the film will need to be advanced and several frames lost. Buy another film back and switch film mid roll.

The Pentax 645 magazines are quite dumb, they have no frame counter, no transport handle, no indicator for begin or end, and no dark slide. After the magazine is inserted in the camera, and the camera switched on, press the shutter-button and the film is automatically advanced to the first frame somewhere at the beginning of the film and the counter in the display shows "1". After 16 frames 6x4 the film is automatically wound to the end and you can remove the magazine. That's it, exactly how you would expect it to work on a 35mm film camera. Also no changes mid-roll (there is no counter on the magazine and no dark slide).

itsdoable · May 30, 2018

This is the picture from the linked thread above (lightproof on the Pentax forum):

The pressure plate is machined down at the edge for 220 (right insert) so that the film channel is a little narrower to account for the lack of paper backing. The simple solution is to add a layer or 2 of tape (aluminium tape?) and build up the machined section so it's flush with the rest of the pressure plate.

The film sits on the inside rails of the camera, and the pressure plate sits on the outside rails. The outside rails are slightly higher so that film channel is approximately the thickness of the film stock, which varies a bit from different manufactures. The purpose of the channel is to keep the film flat. Too thick a channel, and the curl causes the center to curl away. Too thin, and the pressure on the rails can cause the center to buckle in. In cases where the film stock was thick (ie: Ilford, chrome, etc...) the pressure plate would squeeze the film against the rails.

I don't think the pressure on the film will break the camera, as it's part of the design. I'd be more concerned about the effect on film flatness. But a few layers of tape will fix that.

Billy Axeman · May 31, 2018

itsdoable said:
This is the picture from the linked thread above (lightproof on the Pentax forum):
[image]
The pressure plate is machined down at the edge for 220 (right insert) so that the film channel is a little narrower to account for the lack of paper backing. The simple solution is to add a layer or 2 of tape (aluminium tape?) and build up the machined section so it's flush with the rest of the pressure plate.

The film sits on the inside rails of the camera, and the pressure plate sits on the outside rails. The outside rails are slightly higher so that film channel is approximately the thickness of the film stock, which varies a bit from different manufactures. The purpose of the channel is to keep the film flat. Too thick a channel, and the curl causes the center to curl away. Too thin, and the pressure on the rails can cause the center to buckle in. In cases where the film stock was thick (ie: Ilford, chrome, etc...) the pressure plate would squeeze the film against the rails.

I don't think the pressure on the film will break the camera, as it's part of the design. I'd be more concerned about the effect on film flatness. But a few layers of tape will fix that.

+1
Exactly, that's how it is.

The author of the cited link (lightproof) says the inside part of the 220 plate is thicker than the one in the 120, but actually both plates have the same thickness and the 220 plate is made thinner at the edges.

A durable solution to convert the 220 plate could also be to make thin aluminum or brass strips 0.1 mm and mount them in the thinner edges with a bit of two-component epoxy glue (0.05 mm thick). The result should be that the edges are on the same height as the middle part, just as on the plate for the 120 magazine.

Of course the small plastic 'finger' on the side of the magazine (just behind the lock) must be flipped too to make the conversion complete.

P645 Insert - Difference between 120 and 220

Ian Grant

Sirius Glass

Billy Axeman

itsdoable

Billy Axeman

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