220 Film back - Bronica GS-1

Maximus966 · Dec 18, 2024

Hello All!

I was gifted by a old school gent a 6x7 220 film back for my Bronica GS-1. I was looking for 220 film, but found it available next to none...

Being new to the Medium Format world, can I use 120 film in the 220 film back? Any mods or anything to watch out for?

Appreciate your time and feedback for this Medium Format total NOOB!

Regards,

Jorge

EDIT: Before someone comments, be advised, searched and got the message in the image... thus why the post. Thanks!

MattKing · Dec 18, 2024

I have experience with Mamiya 220 backs, not Bronica ones, but most of my comments on the issue apply.
1) the frame counters in a 220 back don't stop at the end of a 120 roll, so if you can load 120 in the back, you have to be very careful to ignore the frame counter when you pass frame 10, and wind through and unload the film after the 10th photo on the roll;
2) 220 film doesn't have backing paper behind most of the film, just leader and trailer paper at each end. That means the 220 film is thinner than the "sandwich" of 120 film and backing paper together. The thicker 120 film plus paper "sandwich" will at the very least put more strain on the winding mechanism in the back, and may result in it being slightly more difficult to wind the film. Back when Mamiya America maintained a Mamiya medium format users forum, they shared advice that extensive use of 120 in a 220 back could cause premature wear of the 220 back.
When you consider the latter advice, it is important to realize that the Mamiya cameras that that advice was directed toward were designed for heavy professional use, and therefore the definition of extensive use was probably much heavier use than you are considering.

The first concern is fairly universal. The second may or may not apply to your camera, depending on how the backs were designed by Bronica.

One thing to understand: the greater thickness of 120 film doesn't affect the plane of focus. That is determined by the film rails, which are in contact with the emulsion side of the film.

Maximus966 · Dec 18, 2024

MattKing said:
One thing to understand: the greater thickness of 120 film doesn't affect the plane of focus. That is determined by the film rails, which are in contact with the emulsion side of the film.

Thanks for your quick reply! The above quote means I would have to put some backing on the film back plate? If so, any specific "laminate", so to speak, to use as the "filler"?

Or basically, as the 120 film and paper is thicker, I wouldn't have to use a backing for the film on the film plate? This secodn one is what I understood is the current scenario of 120 film in 220 back.

Thanks!

MattKing · Dec 18, 2024

Maximus966 said:
Thanks for your quick reply! The above quote means I would have to put some backing on the film back plate? If so, any specific "laminate", so to speak, to use as the "filler"?

Or basically, as the 120 film and paper is thicker, I wouldn't have to use a backing for the film on the film plate? This secodn one is what I understood is the current scenario of 120 film in 220 back.

Thanks!

No, there is nothing that you would add.
The 120 film "sandwich" is thicker than 220, and therefore thicker than what the backs are optimized for.
But before you proceed further, you should wait to hear from the GS-1 users, because there may be some camera specific concerns that my more limited knowledge doesn't extend to.

OAPOli · Dec 18, 2024

I used a 220 back with 120 film on a Bronica SQ-A. No issues. On the pressure plate were two milled sections on the outer edges to compensate for the thinner film. This will lead to slightly higher pressure on the film. You can put a bit of masking tape to fill the space (but it must not be too thick). I assume the same construction is used on the GS-1.

Truzi · Dec 18, 2024

I'll second what MattKing said. I have a GS-1 and have use both 120 & 220 backs. I've not really had any issues, but be careful at the end of the roll. It will continue until it detects the paper tail is out of the way, so it's not like you have to advance twice as much.

The thickness difference between 120 and 220 might affect sharpness/focus slightly, but I'm not that advanced (I just take snapshots), so everything seems fine to me.

Maximus966 · Dec 18, 2024

MattKing said:
No, there is nothing that you would add.
The 120 film "sandwich" is thicker than 220, and therefore thicker than what the backs are optimized for.
But before you proceed further, you should wait to hear from the GS-1 users, because there may be some camera specific concerns that my more limited knowledge doesn't extend to.

Thanks, Matt.

MattKing · Dec 18, 2024

Truzi said:
I'll second what MattKing said. I have a GS-1 and have use both 120 & 220 backs. I've not really had any issues, but be careful at the end of the roll. It will continue until it detects the paper tail is out of the way, so it's not like you have to advance twice as much.

The thickness difference between 120 and 220 might affect sharpness/focus slightly, but I'm not that advanced (I just take snapshots), so everything seems fine to me.

It won't affect focus, because the film rails - not the pressure plate - control where the film sits.
The reverse might create a problem - 220 in a 120 back - but that would be due to there being too much space for thinner 220 film, with the possibility arising that the film wouldn't be held as flat.

Maximus966 · Dec 18, 2024

Truzi said:
I'll second what MattKing said. I have a GS-1 and have use both 120 & 220 backs. I've not really had any issues, but be careful at the end of the roll. It will continue until it detects the paper tail is out of the way, so it's not like you have to advance twice as much.

The thickness difference between 120 and 220 might affect sharpness/focus slightly, but I'm not that advanced (I just take snapshots), so everything seems fine to me.

Thanks, Truzi. Will check and upload later a pic or two of the 220 back then.

Maximus966 · Dec 18, 2024

OAPOli said:
I used a 220 back with 120 film on a Bronica SQ-A. No issues. On the pressure plate were two milled sections on the outer edges to compensate for the thinner film. This will lead to slightly higher pressure on the film. You can put a bit of masking tape to fill the space (but it must not be too thick). I assume the same construction is used on the GS-1.

Thanks also!

Dave Ludwig · Dec 18, 2024

You may get spacing problems between frames. I believe most 120 backs adjust the "pull" of film as the rewind spool gets bigger to keep frame spacing adequate due to increasing spool diameter caused by the paper backing. Due to a lack of backing paper the 220 take up reel may not adjust the pull accordingly and your frame spacing may not be equal. Pressure plates typically release a tiny bit when winding the film, so I would not add thickness to pressure plate. I also do not know if the loading 120 into 220 the "start" position would be the same. You could waste a roll of 120 and mark each frame with a pen through the front of the camera.

Maximus966 · Dec 18, 2024

Hello Gents!

Image on the left is the 120 Film Back… flush all the way.

Image on the right is the 220…. Definitely a mill / step on the top and bottom of the plate.

So those two little steps are the ones that would require a small strip of masking tape applied? Thinking of using a painters blue tape, unless any other is recommended.

Thanks!

OAPOli · Dec 18, 2024

Yes, I used masking tape. Make sure it is 0.10mm or a bit lower. Backing paper is 0.10-0.12mm.

MattKing · Dec 18, 2024

I'd be cautious about adding anything, given that it may interact with the backing leader and trailer papers - particularly the leader.

reddesert · Dec 18, 2024

There is a theoretical difference in the location of the film plane because of the backing paper. This is probably about 0.1mm, which is roughly the thickness of backing paper. For average sharpness and a circle of confusion of 0.05mm, this would be covered by depth of focus for an f/2 lens. For critical sharpness one might want to do a little better.

However, there aren't any really fast lenses for the GS-1 system (due to the modest size leaf shutters it used). The fastest lens is f/3.5. And people often stop down in medium format anyway to get more depth of field.

So IMO you should spend your effort testing the frame spacing, which may be a little irregular, before spending time putting tape on the pressure plate, which is probably going to be near unnoticeable unless it comes off and gets stuck to your film.

MattKing · Dec 19, 2024

reddesert said:
There is a theoretical difference in the location of the film plane because of the backing paper.

This is not how it works.
The position of the film is determined from the front by the film gate/rails, which the emulsion side is in contact with, not what is behind the film.
And the addition of backing paper just means that the film is pushed harder against that gate/those rails.

reddesert · Dec 19, 2024

MattKing said:
This is not how it works.
The position of the film is determined from the front by the film gate/rails, which the emulsion side is in contact with, not what is behind the film.
And the addition of backing paper just means that the film is pushed harder against that gate/those rails.

What I said was confusing. The theoretical difference is because the center of the pressure plate on the 220 back is raised (raised beyond the edge that contacts the outer rails). It is raised by roughly the thickness of the absent backing paper. Which is 0.1mm, and likely difficult to detect in practice in terms of focus offset. Other issues such as film transport can be experimented with by the user.

Maximus966 · Dec 19, 2024

Thinking of the 220 vs the 120 and the film paper backing.... Since the 220 plate compensates for the no-paper backing, would this be an advantage to shoot 35mm film then (no paper backing!) with the spool adapters for 35mm cartridge? Thinking on how to make the best of the 220 with "proper" film thickness...?

And yes, will try a B&W 120 roll in the 220 just for kicks, and report back!

Thank you all for your time and guidance!

Jorge

OAPOli · Dec 19, 2024

MattKing said:
I'd be cautious about adding anything, given that it may interact with the backing leader and trailer papers - particularly the leader.

The tape would be in the milled channels of the pressure plate. That section butts against the outer rails, there is no film or backing paper at that location. And given that the pressure plate is stationary, I don't think there is a risk of the tape coming off.

Because of the milled section, there will be 1) an additional strain on the winding system caused by the thicker film (maybe insignificant); 2) a potential bulge in the film: not at the film rails where it is constrained but everywhere else.

@reddesert I believe the Bronica backs use a measuring roller for film spacing. The latter is thus unaffected by a film type mismatch.

Mike Lopez · Dec 19, 2024

I’ve used 120 film in a 220 back on the GS-1 without a single modification since 2008. No problems at all. None.

Maximus966 · Dec 19, 2024

Mike Lopez said:
I’ve used 120 film in a 220 back on the GS-1 without a single modification since 2008. No problems at all. Non

Thanks, Mike.

abruzzi · Dec 19, 2024

this question comes up frequently for different cameras (probably because 220 backs are much cheaper) but one thing I've never seen brought up is the start indicator. Is the start indicator on 220 film the same distance from the start of the film as it is for the 120 start indicator? I assume since that never comes up as a warning, that they are the same distance? Or at least close enough that it doesn't make that much difference?

OAPOli · Dec 19, 2024

220 film has a longer leader, with two start marks. I believe most cameras use the inner start mark, which is the same distance from the film as on 120 film. There would be no difference for film backs that sense the film linearly. For the backs that account for the increase in the take-up spool diameter via a cam, there is a difference.

I'll revise my prior statement. As @MattKing pointed out there should be no difference in the film plane location due to the milled pressure plate. Most likely the plate will lose contact with the outer rails due to the thicker film. The only effect is added drag, with potentially better film flatness?

reddesert · Dec 19, 2024

Maximus966 said:
Thinking of the 220 vs the 120 and the film paper backing.... Since the 220 plate compensates for the no-paper backing, would this be an advantage to shoot 35mm film then (no paper backing!) with the spool adapters for 35mm cartridge? Thinking on how to make the best of the 220 with "proper" film thickness...?

And yes, will try a B&W 120 roll in the 220 just for kicks, and report back!

Thank you all for your time and guidance!

Jorge

Using a 220 back for 35mm film with spool adapters would be an advantage in any case, because the length of the film in a 220 roll is about the same as a 36 exposure roll of 35mm (about 1.4 meters). Using it in a 120 back, you would likely need a short roll or the back would reach the end long before the roll of film ended.

Maximus966 · Jan 3, 2025

Hello!

Finally received my spool adapters for 35mm roll so it sits in the middle of the 220 film back for my Bronica GS-1.

I have 2 questions:

1. Leader - Any link to a film leader (or related info on size and length) to attach to the film and make the best out of the roll, like the 120 leader? To be honest, I did see something on a website, for whatever reason did not save it, and I cant find it now, no matter how I word it in Google!

2. Viewscreen - any info on a mask for viewing purposes and determine what I would be looking at vs. what will show up on the film? Also, is there any screen available with said markings?

Appreciate your time, as always; Happy 2025 to all!

Regards,

Jorge

220 Film back - Bronica GS-1

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