Help with light leak on Mamiya RB 645 back, please

[tkamiya]

This is frustrating.

I just tested new-to-me Mamiya RB-SD 645 back in the field. As you can see, there is a light leak on bottom of the frame. An odd thing is, this is the only place it appears - overlapping frame 1 and 2 and in between. It happened no where else.

This is a back that came from a well-known source and was in great condition. I don't think it was ever used....

Film was Tri-X.

On the image, you are looking at the film from back side as you can tell from the frame counter number. It is at the bottom of the negative.

Does anyone recognize this pattern? I don't see any damage of any kind on this back. It really looks brand new.

 

[removed-user-1]

Is it possible this happened in loading?

 

[tkamiya]

Here'a another view of the same area.

 

[tkamiya]

Is it possible this happened in loading?

I cannot say it is impossible. I was careful not to despool the film though. Wouldn't loading time problem cause more severe issue?

 

[removed-user-1]

Hmmm. Well, you say the back is in good condition. So, there are no issues with the seals you can see. What about the seal around the dark slide slot (which is inside the back)? If the slide was left out for a while and some light got in, and then you advanced the film through the rest of the frames, you might get a leak near the start of the roll without seeing it on the rest of the frames. Just a guess... if you have to reseal the back, it's very easy to do on the older Pro and Pro-S backs (I've never used a Pro-SD).

 

[tkamiya]

I have no way to see the condition of seals inside the back. This back being SD type, there are only two areas where foam seals actually exist. Hinge area and the dark slide area. One that I can see, the hinge one, looks perfectly good.

If it was a leak from light seal on the darkslide opening, I'd think the problem will appear on the other side of the frame, as that side is the closest to the opening.

I opened the back, loaded the film onto the insert, advanced it to the arrow. Mounted the insert into the back, firmly closed it, latched it, advanced to the frame 1, then pulled out the dark slide.

As you can see, something happened at the very beginning as margin area got some exposure but oddly stopped right outside of the image area, suddenly. Then, a major light leak with interruption took place over and between frame 1 and 2.

I looked at my back closely. I cannot figure this out.

 

[MattKing]

Do you have another dark slide that you could swap out?

Do you have another "shell" that you can switch with this one?

I'm wondering whether the problem could have something to do with the rotating back.

 

[tkamiya]

I have another back, 6x8 power back. No issues with this one.

I don't know if this will help. I just highly processed the image and reversed it. I can clearly see the profile of the leak.

So far, I have not seen anything that matches this profile. Oddly enough, the leak stops before the bottom end of the image.

 

[MattKing]

Could it be flare rather than a leak?

I see there is a bright area behind your subject.

 

[tkamiya]

Yes, but why would a flare go outside of the image area (on the side) and abruptly and cleanly stop (bottom)??

 

[tkamiya]

By the way.... appreciate all the ideas and input. I'm quite baffled. I just cut off that part of film, laying it on various parts of the back. There's nothing that matches that profile.

 

[MattKing]

My guess is that it is flare, and the source of it is outside the image area, but within the much larger 6x7 area of the RB67's optical path.

It is quite strong, and it appears to be piping past the edge of the image.

 

[tkamiya]

645 back has an opening gate that is sized 6x4.5. It sounds plausible but I can't find the way how exposure can take place outside of the gate opening. This image was taken today and this particular one was under shade. The bright area behind it was water. Exposure was 1/250 and f/5.6. It wasn't particularly a bright day....

 

[tkamiya]

Can you think of any other operator induced error that can cause this? What bothers me really is there are 15 shots total. All other shots are entirely fine. Two more shots at this exact location right next to these two frames are fine, too. I'm going to run the test again tomorrow to see if the problem reproduces.

 

[tkamiya]

I found something.

There is a stainless steel roller where the film goes in. It is supposed to keep the film from unspooling. The top edge of the mysterious exposure matches with this piece. I had to load the film under shade but nevertheless outside. I wonder if the film got unspooled and buckled just so that this exposure took place when I loaded the film, and just happened to land where it did??

I just rolled the film back into the frame again and when the arrow is matched, frame 1 is just 4 layers behind the backing paper. With some light piping happening before frame 1, that may be the cause...

 

[tkamiya]

Am I mistaken in thinking I should be able to load 120 film in shade if I am careful?? I've done this on M645 and never an issue like this.

 

[MattKing]

Am I mistaken in thinking I should be able to load 120 film in shade if I am careful?? I've done this on M645 and never an issue like this.

You are not mistaken.

 

[tkamiya]

I was right about something today. Oh, wait, that was yesterday.

 

[tkamiya]

I did another test today.

Loaded the film in dim indoors, advanced the frames to 1, and removed the dark slide. When outside and shot all the frames. During the test, I rotated the back, inserted and removed the slide a few times to simulate typical usage. Condition outside was about two stops brighter than yesterday. I came inside and slid the dark slide in, removed the back, then removed the film.

There WAS a similar light leak but it was well ahead of the frame 1. There was some light piping from the edge but very minor. There was a little more light piping at the end which I assume it happened after the film was taken out of the camera.

So basically, it's good.

Questions to the larger audience....

1) Is this kind of result typical? I am not particularly new to MF. I had M645 Super and Pro before. I don't recall area ahead of frame 1 getting any exposure like this.

2) Above test was basically an ideal condition where I can load and unload film in dim indoor. That won't always happen in the field. Again, I don't recall this kind of problem with M645.