Easy conversion of Pentax 645 220 back to 120

[Kino]

This may be old hat, but I thought it worth posting.

Seems there are only two mechanical differences between the 120 and the 220 Pentax 645 back;

1: A plastic part on the side of the pressure plate. This needs to be simply unscrewed from the back, flipped over and reinstalled with the existing screw or screws.
2. The pressure plate rails outside of the actual film transport area needs to be shimmed approximately 0.15 mm to allow for the backing paper to slide through the gate.

So, with this in mind, I jumped over to Ebay and found a pristine 220 back in the holder for $25; less than half the cost of a similar condition 120 back. I will happily try this trick, as one of my backs have developed an issue with the grounding lug that touches the film gate when the paper backing pulls through. The camera refuses to fire as it is grounded all the time and replacing the internal wire is a real pain, fraught with danger in disassembling the back and getting back together again in proper condition.

According to some responders on the below thread, similar tricks can be performed on the Mamiya 645 backs with a few more steps.

References:

Pentax 645 convert 220 to 120

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...

rangefinderforum.com

P645 Insert - Difference between 120 and 220

Without wishing to appear rude, can I say that this thread is really addressed only to those who have converted a 220 P645 insert to 120 in respect of answers. Anyone contemplating conversion of a 220 to 120 might of course be interested. On the PentaxForums site, there has been a...

www.photrio.com

 

[Wolfram Malukker]

Yep. Some foil tape to shim the pressure plate, and flip the identification tab, and they're good to go. I use aluminum foil tape for ductwork, it's very cheap and durable enough to do the job.

I bought 4 220 backs with the cases for 30$ not that long ago, while a single 120 back with no case was 80$.

 

[pentaxuser]

Yep. Some foil tape to shim the pressure plate, and flip the identification tab, and they're good to go. I use aluminum foil tape for ductwork, it's very cheap and durable enough to do the job.

I bought 4 220 backs with the cases for 30$ not that long ago, while a single 120 back with no case was 80$.

I don't recall any mention of a shimming requirement in the linked thread in which I had a good deal of involvement. For those worried about the straín on the motor by just the adjustment of the part then your solution of aluminium foil tape sounds like a relatively easy and and worthwhile step to take

It isn't quite clear to me what shimming involves, so if at at possible, you could show before and after pictures that involves using the tape that would be very helpful

Until you mentioned the use of tape it sounded as if Kino's shimming might have involved some kind of much more complicated process This is a presumption on my part and I really ought to ask Kino to say exactly what he did as well

Thanks

pentaxuser

 

[Wolfram Malukker]

On a pentax 220 back, the pressure plate has two machined flats on each side, where the pressure plate makes contact with the rails inside the camera body.

The 120 backs do not have the machined flats, the pressure plate is flat. By adding the foil tape shims onto the 220 pressure plate, you can set the two pressure plates into the same location in the camera body, eliminating any worries about overloading the in-body motor. Make sure you apply the tape only to the machined flat, and trim carefully to make sure no sticky bits of conductive foil could get dragged into the camera body.

The silver is where the foil tape is applied.

 

[Kino]

I don't recall any mention of a shimming requirement in the linked thread in which I had a good deal of involvement. For those worried about the straín on the motor by just the adjustment of the part then your solution of aluminium foil tape sounds like a relatively easy and and worthwhile step to take

It isn't quite clear to me what shimming involves, so if at at possible, you could show before and after pictures that involves using the tape that would be very helpful

Until you mentioned the use of tape it sounded as if Kino's shimming might have involved some kind of much more complicated process This is a presumption on my part and I really ought to ask Kino to say exactly what he did as well

Thanks

pentaxuser

This is shown in a couple of pictures (scroll down a bit) in the first link I mentioned as a reference: https://rangefinderforum.com/threads/pentax-645-convert-220-to-120.4763083/

The person uses copper tape, but I was also going to try aluminum tape like Wolfram has done.

 

[Kino]

I bought 4 220 backs with the cases for 30$ not that long ago, while a single 120 back with no case was 80$.

Nice!

 

[LimeyKeith]

I thought this modification was well known, I've been using it successfully for quite a few years now but thanks to Kino for bringing it to light again.

 

[pentaxuser]

This is shown in a couple of pictures (scroll down a bit) in the first link I mentioned as a reference: https://rangefinderforum.com/threads/pentax-645-convert-220-to-120.4763083/

The person uses copper tape, but I was also going to try aluminum tape like Wolfram has done.

Thanks I had either overlooked this description of what to do to "shim" in this thread or it had also appeared on the PentaxForum one but I was unaware of this rangefinder forum

As long as both kinds of metal tape have the same thickness then it looks an easy conversíon

LimeyKeith is there a particular make of tape needed or all are copper or aluminium tape the same thickness?

Thanks

 

[Wolfram Malukker]

My foil tape is 0.005" thick, so about 0.0005" thinner than normal Kodak 120 paper.

This trick works on Mamiya 645 backs too, there is a tab that gets removed and the backing plate shimmed. Not sure if Bronica backs can have the counter tricked, but the pressure plate can be shimmed this way.