[texandrews]

Convert Pentax 645 645n 645nii 220 film back to 120 film back - YouTube

645 220 holder to 120 conversion

Yup, that was it. Not a pin, but something in the pin universe. I remember that it wasn't an arduous fix.

[Smolk]

When I had this camera, I also converted a back this way and noticed no downsides. However, years later there was a post on this site suggesting that such converted 220 spools could damage the winding motor of the 645. It did not sound like a rumour either. I would investigate that if I went down the same route again.

[UncleVanya]

When I had this camera, I also converted a back this way and noticed no downsides. However, years later there was a post on this site suggesting that such converted 220 spools could damage the winding motor of the 645. It did not sound like a rumour either. I would investigate that if I went down the same route again.

That seems dubious, given the low complexity and simplicity of the change. It appears the two end up identical, and I have a tough time thinking about how this could cause any problems, but I guess researching it is in order if you have one of these.

[Smolk]

I know, but it was Pentax engineering info I believe, so not something that can easily be dismissed. And it would be the kind of damage not easily spotted after a few dozens of rolls - but in professional film days, it would be thousands every year. Small differences add up over time.
Still, something to check. It might still be false alarm.

[kaseki]

There is another thread on this topic where I recall we beat the subject to death. Unfortunately, I don't recall the exact condition of the resulting body.

The only question, as far as I know, is whether the fix (in the video) is sufficient to compensate for the difference in film thicknesses, and hence sufficient to make the motor torque requirement for 120 film in the modified 220 holder be the same as with 120 film in a 120 holder. I don't have a 220 holder to compare with my 120 holders.

I also don't recall whether the Pentax source was answering the same question, or whether the question answered was whether one could without harm run 120 film in an unmodified 220 holder.

[asahijock]

I participated in the thread to which reference was made and frankly no final conclusion was reached nor do I think that anyone had any evidence that the 220 to 120 conversion had done any harm. Some 2 years on it would be interesting if anyone since had experienced a problem caused by the conversion causing a strain on the camera's motor

The question that springs to mind is why make did Pentax make the conversion that simple if there was a problem when this was done?

asahijock

[UncleVanya]

I participated in the thread to which reference was made and frankly no final conclusion was reached nor do I think that anyone had any evidence that the 220 to 120 conversion had done any harm. Some 2 years on it would be interesting if anyone since had experienced a problem caused by the conversion causing a strain on the camera's motor

The question that springs to mind is why make did Pentax make the conversion that simple if there was a problem when this was done?

asahijock

My recollection is that there is NO OTHER physical difference between the two holders. Given that the notch is just an indicator to the camera about which holder is inserted it is hard to understand how anything would negatively impact use. Science not speculation should be our guiding principle here.

[kaseki]

I participated in the thread to which reference was made and frankly no final conclusion was reached nor do I think that anyone had any evidence that the 220 to 120 conversion had done any harm. Some 2 years on it would be interesting if anyone since had experienced a problem caused by the conversion causing a strain on the camera's motor

The question that springs to mind is why make did Pentax make the conversion that simple if there was a problem when this was done?

asahijock

I would guess that Pentax' goal wasn't to simplify conversion, but to minimize the number of different parts that had to be kept in inventory. This is a characteristic of good industrial design.

[yucafrita]

My recollection is that there is NO OTHER physical difference between the two holders. Given that the notch is just an indicator to the camera about which holder is inserted it is hard to understand how anything would negatively impact use. Science not speculation should be our guiding principle here.

I remember a thread where it was indicated that the 220 pressure plate itself had a slightly different thickness compared to the 120 holder. This might affect tension and winding and motor.

[UncleVanya]

I remember a thread where it was indicated that the 220 pressure plate itself had a slightly different thickness compared to the 120 holder. This might affect tension and winding and motor.

Ah! That could be a factor.

[leekil]

I never understood why 220 film did not take over from 120. The only advantage of 120 was that old cameras could have a red tinted window in the back to observe the frame number on the paper backing, and that was only safe with orthochromatic B&W film anyway. Both that type of camera and that type of film went into the history books a very long time ago. Every other advantage was with 220 film.

Plenty of old cameras are in use today by contemporary film photographers. Also there are the not-super-old Holga cameras (1990's?) that are popular among toy camera photographers.

[kaseki]

Ah! That could be a factor.

Pentax 645N - 120 film in 220 magazine ? - Page 2 - PentaxForums.com is the page where the two plates (of different thickness) are shown. (I think I'm using 15 message pages.)

From message 40 of the referenced thread:

"My recollection is that the 220 plate was not thicker, but the hard-points that mated with the film gate was machined down about the thickness of the paper, so as people have pointed out, the gap was thinner to accommodate the film without backing paper.

"I added tape to the edge of the 220 plate above, so that the machined area at the edge of the plate was now flush with the rest, as in the 120 plate. I used aluminium foil tape. Much easier than machining down a plate."

See also messages 48 and 55 of that thread.

My opinion: It is feasible to reverse the plastic part to get the count correct, and feasible to shim the 220 pressure plate so that it emulates a 120 pressure plate. The result will achieve "120 film" drag until the shim attachment scheme fails. So it is incumbent on the modifier to pay attention to the shim attachment means, particularly if many rolls are passed over them and/or they are subjected to temperatures that might affect the bonding agent. Whether this is also cost-effective vs. buying 120 backs is a question best answered by the wallet holder.

[UncleVanya]

Thanks that clears it up.

[texandrews]

Pentax 645N - 120 film in 220 magazine ? - Page 2 - PentaxForums.com is the page where the two plates (of different thickness) are shown. (I think I'm using 15 message pages.)

From message 40 of the referenced thread:

"My recollection is that the 220 plate was not thicker, but the hard-points that mated with the film gate was machined down about the thickness of the paper, so as people have pointed out, the gap was thinner to accommodate the film without backing paper.

"I added tape to the edge of the 220 plate above, so that the machined area at the edge of the plate was now flush with the rest, as in the 120 plate. I used aluminium foil tape. Much easier than machining down a plate."

See also messages 48 and 55 of that thread.

My opinion: It is feasible to reverse the plastic part to get the count correct, and feasible to shim the 220 pressure plate so that it emulates a 120 pressure plate. The result will achieve "120 film" drag until the shim attachment scheme fails. So it is incumbent on the modifier to pay attention to the shim attachment means, particularly if many rolls are passed over them and/or they are subjected to temperatures that might affect the bonding agent. Whether this is also cost-effective vs. buying 120 backs is a question best answered by the wallet holder.

Good catch. But sometimes the cost is not the factor, but availability. When I still had my 645N just before I got my Z in 2014, that's when 220 began to disappear---and so did the 120 backs! Maybe it's different now.

[Smolk]

Pentax 645N - 120 film in 220 magazine ? - Page 2 - PentaxForums.com is the page where the two plates (of different thickness) are shown. (I think I'm using 15 message pages.)

From message 40 of the referenced thread:

....

Thanks! That does clarify matters. I had switched off before the last posts in this thread, which explain the issue of thickness of the plate and the film. Great!