Pentax 645 convert 220 to 120

[shawn]

For anyone using the Pentax 645/N/NII cameras you will likely find that the 120 cartridges cost about 10x the price of the 220 cartridges. Turns out the 220 cartridges can be converted to 120 very easily.

First step is to unscrew a small plastic piece and flip it over to tell the camera the insert is a 120 insert. This one has already been flipped. Some have 1 screw and a stud holding this on, some have 2 screws.

The other change is to alter the pressure of the pressure plate as there is a very subtle difference between the 220 and 120 pressure plates.

This is a 120...

This is a 220 plate...

Notice the very slight recess at the edge of the 220 plate. That is outside of the film area but fits onto a second gate in the camera.

They are the outer gates in this picture.

This lets the plate move further into the camera to account for no backing paper to keep pressure consistent between 120 and 220 film. If we don't compensate for this the 120 film will not change position (the actual film gate sets this) but it will have more pressure on the film than with a 120 plate. I've seen a few accounts of people just swapping the plastic tab and then the camera seeming to struggle a little more with film advance.

A little copper tape will correct for this.

There is no movement at these positions, it is strictly to set the pressure so no worries about the advancing film pulling the tape off.

Shawn

 

[Retro-Grouch]

Thanks, Shawn! Very helpful and a potential money saver next time I buy more cartridges.

 

[OlivierAOP]

Thanks for that! I checked on the Mamiya 645 inserts and it is very similar. The 220 insert has milled edges on the pressure plate and a triangular piece (held by 2 screws) on the top RHS of the insert. It raises a little pin inside the film chamber which I guess connects to the counter mechanism. If you remove that piece the counter will stop at 15. Neat.

The Bronica SQ 220 backs also have the milled edges. I'll see if one can trick the counter as well.

 

[shawn]

Cool, that is great this basic trick works for the Mamiya 645 too.

Shawn

 

[wlbarkman]

An easy fix. Thank you. I used copper tape, and noticed that there is still a very slight lip, and it looks like there's one in your photo example. Can we assume that it doesn't need to be perfectly flush?