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.

[rthomas]

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?

[rthomas]

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)??