Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-28-2018, 07:38 PM   #1
Loyal Site Supporter
Loyal Site Supporter
cdd29's Avatar

Join Date: Sep 2016
Location: Southern Indiana
Photos: Gallery
Posts: 955
120 film using a 220 back - 645N

Looking at a 645N with a 220 back. Not finding 220 film for sale anywhere. Can a 120 roll be used in a 220 back? BTW, totally new to medium format film. haven't found any 220 film or remember seeing a 120 babk for it.


Last edited by cdd29; 10-29-2018 at 06:53 PM.
10-28-2018, 08:34 PM   #2
Veteran Member




Join Date: Sep 2017
Location: Medellín
Posts: 1,322
I know a 220 back can be modified to take 120 film, but other than the pressure plate, I have no clue. You could try researching a bit about how to modify them.

10-28-2018, 09:57 PM   #3
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,137
Best solution is to buy some 120 backs via eBay unless you can find one at a local camera store.

I can't help with 220 film. I have seen some listed somewhere in the past few months but I don't know how obsolete the listing might be. All my backs are for 120. Some camera hacks can be found on this forum, but I wasn't impressed with the effort-benefit over just buying the correct back.
10-29-2018, 01:36 AM   #4
Pentaxian
Andrea K's Avatar

Join Date: Mar 2009
Location: Rome, Italy
Posts: 822


10-29-2018, 10:32 AM   #5
Pentaxian




Join Date: Jul 2009
Location: Pugetopolis
Posts: 11,008
Yeah don't count on finding any 220 film anymore.
10-29-2018, 06:07 PM   #6
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,137
Interesting. Clearly a eureka solution. All the discussion of this topic that I recall previously reading on this forum had to do with different thicknesses of pressure plates.
10-30-2018, 02:38 PM   #7
Senior Member




Join Date: Mar 2011
Location: Northants, England
Posts: 167
OP,just a small word of warning. There has been one or two threads on this subject and the last one if I recall presented an argument that the pressure plate require altering as well, claiming support from a ex Pentax repairman for this. It was not the simple fix that we all had assumed it to be. However as I recall things, that poster was in a minority of one. Those who had altered the 220 back as has been mentioned above did not, as I recall, cite any difficulties with 120 film after the alteration. I cannot comment on any difficulties as I was fortunate enough to obtain two extra 120 backs so have not had to try altering a 220 back

You might want to search for that thread

asahijock

10-30-2018, 04:17 PM   #8
Loyal Site Supporter
Loyal Site Supporter
ivanvernon's Avatar

Join Date: Oct 2012
Location: Medina, OH
Photos: Albums
Posts: 7,224
QuoteOriginally posted by cdd29 Quote
Looking at a 645N with a 220 back. Not finding 220 film for sale anywhere. Can a 120 roll be used in a 220 back? BTW, totally new to medium format film. haven't found any 220 film or remember seeing a 120 babk for it.
You can buy 220 film on eBay. However, our local pro camera shop here in Cleveland, OH, only carries 120, says not enough demand to stock 220.
10-30-2018, 05:38 PM   #9
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,137
QuoteOriginally posted by Brooke Meyer Quote
The pressure plate on Pentax 645 backs is spring loaded. The film is tensioned across the plate. The only difference is the length of the roll. 220 is longer because its thinner without backing, more can fit on the spool. There is no way to differentiate thickness. The tab position is simply an indicator of how long and therefore how many frames are on the roll.
Put a roll of 220 in a 120 back and the pictures will be fine except the camera wiil rewind half way through the roll.
This suggests that the only parameters left of possible concern would be differences in plate spring tension affecting winding force, or plate surface treatment changes to avoid scratching the naked 220 film. I don't see any scratches in Brooke's image above, so that may be a non issue. If spring tension differs, it might be difficult to notice any effect.

---------- Post added 30th Oct 2018 at 20:46 ----------

This was a major thread on this topic [that I had forgotten the details of]:
Pentax 645N - 120 film in 220 magazine ? - PentaxForums.com

Last edited by kaseki; 10-30-2018 at 05:57 PM.
10-31-2018, 07:19 AM   #10
Loyal Site Supporter
Loyal Site Supporter




Join Date: Dec 2017
Photos: Gallery | Albums
Posts: 1,137
QuoteOriginally posted by Brooke Meyer Quote
If you look at and handle a 645 back, you'll feel the very light spring load against the pressure plate. No one could make sets of springs in a volume manufacturing process that could reliably differentiate a few thousandths of an inch of thickness with the identical mechanical drive mechanism in a body that drives all backs. The camera winds the film. The tension and torque have to be constant regardless of back. The only difference is thinner, longer film. Or in the case of 220 to 120, thicker, shorter film. All it has to do is hold the film taut and flat against a mechanical surface. Film thickness is a rounding error compared to variances in lens mount and focus tolerances.
Agreed. However, the pressure plate comparison photo on page [Ed.] 2 of the topic I linked to above shows that Pentax used a thicker plate for the 220. We should assume a reason exited before assuming no reason existed.

QuoteOriginally posted by Brooke Meyer Quote
This is a case where going "off recipe" is rewarding and practical. But if it's uncomfortable, by all means, buy 120 backs.
All my backs are 120 backs, so I have no immediate way of scrutinizing the design details.

Last edited by kaseki; 10-31-2018 at 06:00 PM.
10-31-2018, 08:49 AM   #11
Senior Member




Join Date: Mar 2011
Location: Northants, England
Posts: 167
QuoteOriginally posted by kaseki Quote
Agreed. However, the pressure plate comparison photo on page 3 or 4 of the topic I linked to above shows that Pentax used a thicker plate for the 220. We should assume a reason exited before assuming no reason existed.

.
That, I think, precisely summarises what the poster said in a previous thread and claimed to have the support of an ex Pentax repairman

It does not affect me and you are in a similar position but give the price differential between the two backs and certainly in the U.K. the difficulty of obtaining a 120 back at any price then we really could do with statements from those who have converted a 220 back to 120 about their success or otherwise.

If I were needing a 120 back and could only obtain 220 backs or were facing a choice of $70 extra for a 120 or a simple alteration of say 15 mins for $70 less then I'd want to be sure that the alteration will not give me problems

asahijock
10-31-2018, 08:55 AM   #12
Veteran Member




Join Date: Sep 2017
Location: Medellín
Posts: 1,322
One just has to guarantee less pressure from a 220 back. It would be more difficult to mod a 120 back to 220 because of the lack of backing the strip is thinner, thus film flatness is not guaranteed without proper pressure.
On the 67, the pressure plate just drops a bit further for 220 film. And one just has to switch the counter. An RB67 220 back would just be used until it marks 10.

10-31-2018, 10:46 AM   #13
Pentaxian
Lord Lucan's Avatar

Join Date: Sep 2017
Location: South Wales
Photos: Gallery
Posts: 2,899
QuoteOriginally posted by Brooke Meyer Quote
The only difference is the length of the roll. 220 is longer because its thinner without backing, more can fit on the spool. There is no way to differentiate thickness. The tab position is simply an indicator of how long and therefore how many frames are on the roll.
Put a roll of 220 in a 120 back and the pictures will be fine except the camera wiil rewind half way through the roll.
I would disagree with that. There are two differences between 120 and 220, in fact you say them yourself :-

1) The film is twice as long.
2) The film has no backing paper other than the leader and tail. (Of course, it is this that allows (1).)

As for rewinding, I don't know the 645N, but no 120/220 camera I have ever handled had a rewind : the film just winds onwards to the take-up reel where it stays until processing.

There is a different pressure plate requirement between a 120 back and a 220 back. The gate in front of the film against which it is pressed stays the same, but a 220 pressure plate must be slightly further forward by the thickness of the paper that 120 film would have. This might not sound a lot, but it is critical to holding the film flat without excessive friction. On fixed back cameras like the Pentax 6x7 this is done by the user shifting the plate sideways slightly to place it onto a different step. For 220 film, the back will also of course need to be capable of counting to a higher number, but the 6x7 body can cater for the higher count anyway.
10-31-2018, 12:09 PM   #14
Veteran Member




Join Date: Sep 2017
Location: Medellín
Posts: 1,322
QuoteOriginally posted by Lord Lucan Quote
I would disagree with that. There are two differences between 120 and 220, in fact you say them yourself :-

1) The film is twice as long.
2) The film has no backing paper other than the leader and tail. (Of course, it is this that allows (1).)

As for rewinding, I don't know the 645N, but no 120/220 camera I have ever handled had a rewind : the film just winds onwards to the take-up reel where it stays until processing.

There is a different pressure plate requirement between a 120 back and a 220 back. The gate in front of the film against which it is pressed stays the same, but a 220 pressure plate must be slightly further forward by the thickness of the paper that 120 film would have. This might not sound a lot, but it is critical to holding the film flat without excessive friction. On fixed back cameras like the Pentax 6x7 this is done by the user shifting the plate sideways slightly to place it onto a different step. For 220 film, the back will also of course need to be capable of counting to a higher number, but the 6x7 body can cater for the higher count anyway.
I think he ment wind, not rewind.

10-31-2018, 01:53 PM   #15
Senior Member




Join Date: Mar 2011
Location: Northants, England
Posts: 167
For anyone interested the original thread to which I referred in on page 3 and was started by Matus in 2010 and eventually ended in May of this year. Someone called Lightproof got a message from Eric who appears to be an acknowledged expert on Pentax repairs and he said that the difference in the configuration of the pressure plate means that the conversion makes the motor work harder to wind the film with a risk to the motor's life. Lightproof then supplied pictures of the two pressure plates and based on these there is indeed a difference.

I asked if Eric had any evidence of motor problems arising as a result of the conversions but none was forthcoming. His advice was simply "Don't do it" which is fine is there are plenty of 120 inserts and there probably are from e-bay sellers in Japan but in the longer term, Eric's advice if adhered to, will result in a whole lot of 220 inserts being fit for scrap only.

A pity that there is no evidence of damage from Eric or other Pentax repairmen. If you take 12 rolls a year and expect to use the P645N for say 10 years maybe you can expect no problems. If you use 120 rolls per year for 10 years then maybe things would be different - I just don't know and if anyone else knows he is not revealing the information.


I suspect this thread(s) on insert conversions will remain inconclusive in terms of definitive proof of damage. It will remain a case of " You pays your money and takes your choice

asahijock
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
645d, 645n, 645z, camera, film, medium format, pentax, plate, pressure plate, roll, tension
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax 645N - 120 film in 220 magazine ? Matus Pentax Medium Format 63 03-15-2019 05:29 PM
For Sale - Sold: REDUCED: Mamiya 645af w/ 80mm 2.8, film back, strap, and some 120/220 rolls. boosted03gti Sold Items 16 11-15-2011 11:32 AM
[Pentax 645N] Film insert/back 120 veraikon Pentax Medium Format 2 03-26-2010 01:59 AM



All times are GMT -7. The time now is 11:00 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top