Is this poor film flatness or a lens problem (RB67 Pro-S, 220 film back, 50mm Sekor C)?

Certain Exposures · Sep 4, 2023

Hello:

I could use your help diagnosing this problem.

The issue

Take a look at the sample images in this Imgur link. Notice the linear areas of blur and slight darkness compared to the rest of the frames. These are crops from a single 6x7 frame. The blur and darkness wrap around each edge of every frame. Imagine a 6x7 "vignette" like this around every shot. Otherwise, the negatives look ok.

Additional info

1. I shot 120 film in this 220 film back.

2. I intentionally didn't advance the film to the start arrow before loading to see if I could get a partial 11th frame.

3. The front element of the 50mm Sekor C has a few pinpoint markings on it. I see a few signs of haze and dust.

4. I shot with and without a UV filter. The aberrations are still there regardless.

5. This is the first time I've used both the 50mm lens the first time and this 220 back. I have used a different lens and 220 back (loaded with 120 film) on this camera body without a similar issue. Edit: I underlined this for emphasis. I believe it's a key detail.

My theory

I have a hard time believing that the lens caused this because of how uniform the aberrations are. My best guess is that I started the film roll too early, and this caused the film to be just slightly unflattened.

Unfortunately, I won't have time to test this for a while. I need to make a decision about whether or not to send either part back.

xkaes · Sep 4, 2023

I'd go with #1 or #2 or both.

Using 120 throws the flange distance off. Throw in #2, and who knows.

I'd say try it again -- removing #1 & #2.

Sirius Glass · Sep 4, 2023

120 and 220 films are different thicknesses. That is probably part of the problem.

Dustin McAmera · Sep 4, 2023

I did a search of Photrio for the phrase '120 film in a 220 back'. Previous threads about that are full of replies saying that the pressure plate holds the film up to the rails, and it's the rails that set its position, so using a 22 back shouldn't of itself leave your film off the plane of focus. One said that Mamiya used to warn that the extra thickness of the backing paper might lead to your 220 back needing service sooner.

I'm struck by the curved edge of the frame: on the left of each cropped section as displayed. Is that edge the side adjacent to the next frame, or is that parallel to the film edge? If it's adjacent to the next frame, it seems as though the film must have been bowing through the gate (but it's late, and I may be picturing it wrong). If that was happening when you closed the film back up, I think you'd have noticed. I'd check that the supply spool doesn't turn too freely.

Certain Exposures · Sep 4, 2023

I added formatting to my initial post based on the replies so far. I cannot rule out #1 as the cause. I do think it (probably) needs another contributing factor.

xkaes said:
I'd go with #1 or #2 or both.

Using 120 throws the flange distance off. Throw in #2, and who knows.

I'd say try it again -- removing #1 & #2.

Unfortunately, I won't have time to try before making my decision. I'll update if or when I try again and remove #2. Do you know anyone selling fresh 220 film?

Sirius Glass said:
120 and 220 films are different thicknesses. That is probably part of the problem.

Yes, it's possible.

Dustin McAmera said:
I did a search of Photrio for the phrase '120 film in a 220 back'. Previous threads about that are full of replies saying that the pressure plate holds the film up to the rails, and it's the rails that set its position, so using a 22 back shouldn't of itself leave your film off the plane of focus. One said that Mamiya used to warn that the extra thickness of the backing paper might lead to your 220 back needing service sooner.

I'm struck by the curved edge of the frame: on the left of each cropped section as displayed. Is that edge the side adjacent to the next frame, or is that parallel to the film edge? If it's adjacent to the next frame, it seems as though the film must have been bowing through the gate (but it's late, and I may be picturing it wrong). If that was happening when you closed the film back up, I think you'd have noticed. I'd check that the supply spool doesn't turn too freely.

Your first paragraph matches my experience so far.

The curved edge you're referring to is on the left-hand side of the frame if you were staring down at it on a loupe on a light table. It also appears on the right-hand side of the frame. I see a slightly less dramatic curved edge on the frames of 120 rolls I shot in a 220 back that didn't show this problem.

It would be helpful if someone else who shoots 120 rolls in 220 Mamiya RB67 Pro-S backs could confirm whether or not they see a similar curve.

Is the "supply" spool the left-hand spool? If so, then how would you describe it "turn[ing] too freely?" Also what would the "bowing through the gate" sensation feel like?

Dustin McAmera · Sep 4, 2023

Certain Exposures said:
Is the "supply" spool the left-hand spool?

Yes - the one with the unexposed film on it. I was kind of thinking aloud, (I have to admit I don't have an RB67, but I use a Century Graphic, and the film backs are similar). I have now been and looked at some RB67 photos at Flickr, and I think the flared corners are quite normal with some film holders.

My half-an-idea was that if the film bulged forward out of the film gate into the camera body, you'd get curved edges to the picture, and the edges of the film wouldn't sit properly against the edges of the gate. I don't know what would cause that in an RB67, whereas I have some old folders where letting the bellows unfold themselves in an uncontrolled way will 'suck' the film through the gate. Anyhow, it seemed to me that if there wasn't much drag on the supply spool, it would be easier for the film to do that. ... but now I see those flared corners aren't that unusual, I don't think that's what's happening.

MattKing · Sep 4, 2023

If this involves a 220 insert that has been used with a lot of 120 film, you might be seeing the effects of that extra wear that Mamiya America used to warn about. It looks like the pressure plate isn't providing sufficient even pressure to keep the film flat against the rails.
A 50mm lens used with non-flat film will evidence the problem somewhat more than a longer focal length used with non-flat film.
If you have only tested this with a single roll, I would generally recommend testing it again with another roll from a distinctly different batch, just in case you happened to have used a roll with some sort of moisture or other irregularity for your first test.
And yes, the correct terms for what we generally refer to as an RB67 "back" are actually a combination of an outer shell and an insert, although almost no-one ever swaps inserts and outer shells or calls them anything but a "back".

reddesert · Sep 5, 2023

I don't understand how film unflatness would cause a dark border around the frame. Did you take photos of a relatively bright scene, and did you use a lens hood? There was a lengthy thread recently about a similar dark shadow at the edge of the frame (in a Hasselblad), where the eventual consensus was that there was scattered light from the unshaded image circle within the camera. and the dark border was the film gate shadowing the film from the internally scattered light.

#3 and #4, lens markings and UV filter, have no effect on the issue.

You can just test film unflatness by sacrificing a few exposures of a 120 film. Load it up, wind it to the 1st frame, and pop the back off and pull the darkslide. If you do this in a dimly lit room you probably can inspect the film while fogging only the one exposure and not the adjacent exposures.

Nobody really makes 220 film anymore (except Shanghai). The difference between 220 and 120 is the thickness of the backing paper. It should be hard to see any focus offset except with very fast lenses (more open than f/4 or so). However, since the RB67 backs reverse-curl the film, like many backs, tightness of the film load onto the spool and winding could affect flatness.

MattKing · Sep 5, 2023

reddesert said:
I don't understand how film unflatness would cause a dark border around the frame.

It has to be very un-flat - the film needs to be making inconsistent contact with the rails.

Ian C · Sep 5, 2023

I looked at the photos linked in post 1.

Check the function of the pressure plate in the film back. The images look as though the pressure plate is not holding the film flat against the registration rails adjacent to the film gate.

Alan Edward Klein · Sep 5, 2023

Try a 120 back and if OK discard the 220 back.

Certain Exposures · Sep 5, 2023

Dustin McAmera said:
Yes - the one with the unexposed film on it. I was kind of thinking aloud, (I have to admit I don't have an RB67, but I use a Century Graphic, and the film backs are similar). I have now been and looked at some RB67 photos at Flickr, and I think the flared corners are quite normal with some film holders.

My half-an-idea was that if the film bulged forward out of the film gate into the camera body, you'd get curved edges to the picture, and the edges of the film wouldn't sit properly against the edges of the gate. I don't know what would cause that in an RB67, whereas I have some old folders where letting the bellows unfold themselves in an uncontrolled way will 'suck' the film through the gate. Anyhow, it seemed to me that if there wasn't much drag on the supply spool, it would be easier for the film to do that. ... but now I see those flared corners aren't that unusual, I don't think that's what's happening.

Thank you for following up on this. I was starting to wonder because I don't have another 6x7 camera to compare negatives with.

MattKing said:
If this involves a 220 insert that has been used with a lot of 120 film, you might be seeing the effects of that extra wear that Mamiya America used to warn about. It looks like the pressure plate isn't providing sufficient even pressure to keep the film flat against the rails.
A 50mm lens used with non-flat film will evidence the problem somewhat more than a longer focal length used with non-flat film.
If you have only tested this with a single roll, I would generally recommend testing it again with another roll from a distinctly different batch, just in case you happened to have used a roll with some sort of moisture or other irregularity for your first test.
And yes, the correct terms for what we generally refer to as an RB67 "back" are actually a combination of an outer shell and an insert, although almost no-one ever swaps inserts and outer shells or calls them anything but a "back".

Thanks. It will be a while before I get to try this again with a similar wide lens. I'll update this when I do.

reddesert said:
I don't understand how film unflatness would cause a dark border around the frame. Did you take photos of a relatively bright scene, and did you use a lens hood? There was a lengthy thread recently about a similar dark shadow at the edge of the frame (in a Hasselblad), where the eventual consensus was that there was scattered light from the unshaded image circle within the camera. and the dark border was the film gate shadowing the film from the internally scattered light.

#3 and #4, lens markings and UV filter, have no effect on the issue.

You can just test film unflatness by sacrificing a few exposures of a 120 film. Load it up, wind it to the 1st frame, and pop the back off and pull the darkslide. If you do this in a dimly lit room you probably can inspect the film while fogging only the one exposure and not the adjacent exposures.

Nobody really makes 220 film anymore (except Shanghai). The difference between 220 and 120 is the thickness of the backing paper. It should be hard to see any focus offset except with very fast lenses (more open than f/4 or so). However, since the RB67 backs reverse-curl the film, like many backs, tightness of the film load onto the spool and winding could affect flatness.

Hmmm....thank you. I think you could be on to something. I took these photos early in the afternoon. The sun was still at its highest point and I did not use a lens hood (I don't have one). The negatives show some light bleed around the edges. I will upload an example later. However, why would the shadowed area also appear more out of focus if scattered light was the cause?

Ian C said:
I looked at the photos linked in post 1.

Check the function of the pressure plate in the film back. The images look as though the pressure plate is not holding the film flat against the registration rails adjacent to the film gate.

Thanks, I will.

Alan Edward Klein said:
Try a 120 back and if OK discard the 220 back.

Not so fast! I am frugal. 220 backs are 1/3 the cost of 120 backs. I'd be willing to keep using this back even if I cannot fix the problem because I can always crop out the shaded/out of focus area. I do want to fix it though because I prefer not to crop.

Sirius Glass · Sep 5, 2023

Certain Exposures said:
Not so fast! I am frugal. 220 backs are 1/3 the cost of 120 backs. I'd be willing to keep using this back even if I cannot fix the problem because I can always crop out the shaded/out of focus area. I do want to fix it though because I prefer not to crop.

It would be better to spend money for a good working 120 back than suffer and loose photographs limping along with a 220 back. I personally find that 220 backs make great bookends, door stops and wheel chocks.

Certain Exposures · Sep 5, 2023

Sirius Glass said:
It would be better to spend money for a good working 120 back than suffer and loose photographs limping along with a 220 back. I personally find that 220 backs make great bookends, door stops and wheel chocks.

+1 for your sense of humor .

Do you have any RB67 Pro-S 220 backs you don't want? I'd take them. I need more.

Here is a test frame I exposed with 120 in a 220 for anyone curious:

(http://imgur.com/a/7Hd3xLs)
Edit: does this site "save" an image from Imgur and create its own "permanent" copy in a database somewhere? I added and deleted the Imgur link a few times because the description shown here would not update when I changed it on Imgur.

Donald Qualls · Sep 5, 2023

Sirius Glass said:
I personally find that 220 backs make great bookends, door stops and wheel chocks.

Well, and with extremely minor mods (to make the counter drive roller work as a single piece instead of the tire rotating independent of the main axle), they work great for shooting 35 mm, since a) it has no backing and is similar thickness to 220, and b) a 135-36 is about the same length as a 220 roll. With a little more effort, one could add a mask and auxiliary rails to improve film flatness with the 35 mm.

Sirius Glass · Sep 5, 2023

Certain Exposures said:
+1 for your sense of humor .

Do you have any RB67 Pro-S 220 backs you don't want? I'd take them. I need more.

Here is a test frame I exposed with 120 in a 220 for anyone curious:

(http://imgur.com/a/7Hd3xLs)
Edit: does this site "save" an image from Imgur and create its own "permanent" copy in a database somewhere? I added and deleted the Imgur link a few times because the description shown here would not update when I changed it on Imgur.

I speak Hasselblad. I never got an RB67 because I hater rolling a camera on its side for a portrait shot and I do not want to have to wear a truss just to carry a camera around.

Sirius Glass · Sep 5, 2023

Donald Qualls said:
Well, and with extremely minor mods (to make the counter drive roller work as a single piece instead of the tire rotating independent of the main axle), they work great for shooting 35 mm, since a) it has no backing and is similar thickness to 220, and b) a 135-36 is about the same length as a 220 roll. With a little more effort, one could add a mask and auxiliary rails to improve film flatness with the 35 mm.

Can that be done with a Hasselblad back? Although I am not sure why I would want to shoot 35mm film in a 6x6 camera.

Donald Qualls · Sep 5, 2023

I wouldn't know; I've never handled a 'Blad or any of its accessories. The narrower frame (56 mm or so vs. 67 mm on the RB67) makes the 35 mm less panoramic seeming, anyway. 35 mm in a 6x7 is close to XPan format, and the RB covers almost all of Xpan's focal lengths (albeit it's a lot heavier, it's also a used car cheaper and less likely to break irreparably without warning).

Sirius Glass · Sep 5, 2023

Donald Qualls said:
I wouldn't know; I've never handled a 'Blad or any of its accessories. The narrower frame (56 mm or so vs. 67 mm on the RB67) makes the 35 mm less panoramic seeming, anyway. 35 mm in a 6x7 is close to XPan format, and the RB covers almost all of Xpan's focal lengths (albeit it's a lot heavier, it's also a used car cheaper and less likely to break irreparably without warning).

XPAN, hmmm, a better reason to have GAS.

Donald Qualls · Sep 5, 2023

Sirius Glass said:
XPAN, hmmm, a better reason to have GAS.

I wouldn't buy one even if I could afford it, since electronic parts are no longer available from either Hasselblad or Fuji. I can get an RB67, lenses to cover the Xpan's range, multiple 220 film backs, CLA for everything, and a gym membership for five years for less than an Xpan.

Sirius Glass · Sep 5, 2023

Donald Qualls said:
I wouldn't know; I've never handled a 'Blad or any of its accessories. The narrower frame (56 mm or so vs. 67 mm on the RB67) makes the 35 mm less panoramic seeming, anyway. 35 mm in a 6x7 is close to XPan format, and the RB covers almost all of Xpan's focal lengths (albeit it's a lot heavier, it's also a used car cheaper and less likely to break irreparably without warning).

Sirius Glass said:
XPAN, hmmm, a better reason to have GAS.

Donald Qualls said:
I wouldn't buy one even if I could afford it, since electronic parts are no longer available from either Hasselblad or Fuji. I can get an RB67, lenses to cover the Xpan's range, multiple 220 film backs, CLA for everything, and a gym membership for five years for less than an Xpan.

I meant XPAN capability at much lower prices. Definitely food for thought.

Donald Qualls · Sep 5, 2023

If you want Xpan capabiliity, you only need three lenses -- 90, 65, 50, and a 0.45x filter for the 50. The filter will distort a little, but it won't be noticeable in the 24x67 frame (I can see it on the 6x7, but it's in the upper and lower quarter, and then only noticeable with straight lines in that part of the frame).

reddesert · Sep 5, 2023

Certain Exposures said:
Hmmm....thank you. I think you could be on to something. I took these photos early in the afternoon. The sun was still at its highest point and I did not use a lens hood (I don't have one). The negatives show some light bleed around the edges. I will upload an example later. However, why would the shadowed area also appear more out of focus if scattered light was the cause?

I meant only that you probably have two issues: lens flare and shadowing is the likely cause of the dark borders, and film unflatness could be the cause of the unsharp images and possible wavy borders. I doubt it's the lens, although I can't know. Issues like flare from bright sky are more likely to show up with a wide angle.

Trying to use 120 film in a 220 back is a perfectly reasonable economy and generally should work with the largest downside being possible irregular frame spacing toward the end of the roll. But it's an off-label use, so may need extra care, e.g. attention to loading.

Running 35mm film through a 220 Hasselblad back (or similar cuboid 6x6 cameras and TLRs) is somewhat less attractive because the film path is vertical, so you have to turn the camera on its side for landscape. It's a bit more straightforward in a camera with a horizontal film path - most 6x7, some 6x6 like the Pentacon 6 or Kiev 60. I await the person who can promote the Kiev 60 as the indigent weightlifter's XPAN.

Sirius Glass · Sep 5, 2023

Donald Qualls said:
If you want Xpan capabiliity, you only need three lenses -- 90, 65, 50, and a 0.45x filter for the 50. The filter will distort a little, but it won't be noticeable in the 24x67 frame (I can see it on the 6x7, but it's in the upper and lower quarter, and then only noticeable with straight lines in that part of the frame).

That would be the 100mm, 80mm and 50mm lenses for that.

btaylor · Sep 5, 2023

Sirius Glass said:
I never got an RB67 because I hater rolling a camera on its side for a portrait shot

RB: rotating back. It’s the Bronica GS-1 that needs to be rolled on its side for portraits.

I am aspect ratio agnostic. I do have a soft spot for 6x6 though

Is this poor film flatness or a lens problem (RB67 Pro-S, 220 film back, 50mm Sekor C)?

Certain Exposures

xkaes

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Dustin McAmera

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Is this poor film flatness or a lens problem (RB67 Pro-S, 220 film back, 50mm Sekor C)?

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