Help with light leak please

[stephen t]

<p>Hey all. I've got a ETRS with the old model (one latch) film back. I've attached a low resolution image (scanned with film strips in a Print File sheet and the file size substantially reduced, but the "leak" is quite noticable in the image).<br>

I can't recall anything "strange" happening the other day, except perhaps that there were no mosquitoes in the swamp.<br>

The film was developed in a Paterson 4 tank and the film was loaded on a Paterson plastic reel. It came out of the tank and off the reel just fine, so it can't be a developing issue. The reel was loaded in the darkroom with no stray light.<br>

The first image on the roll, thus the one most shielded from extraneous light, I suppose (the upper right one on the scan) has no issue. The third from the bottom left has no issue. All the others have that strange band. Two different lenses were used, 75mm and 150mm, so it shouldn't be a lens/shutter issue.<br>

Watching the action of the mirror with the lens and back removed indicate proper operation.<br>

The film wasn't subjected to any unusual conditions that I can remember.<br>

I checked the larger seals on the film back and they appear OK. I went ahead tonight and added wool thread along the sides of the channels on the back.<br>

Anybody have any ideas what may have caused this?? (This is my first time uploading an image in a post - I followed the FAQ re: uploading to my "gallery." If there is another way that I should use, I will welcome suggestions).</p>

<p>http://www.photo.net/photo/17989567</p>

[User_502260]

<p>This doesn't look like a shutter problem or a developing problem. I wonder whether it has something to do with the mirror. </p>

[stephen t]

<p>Jeff, I wondered about that myself. When the button is pushed, the mirror goes up and remains there until the film advance/cocking wheel is turned. It isn't hanging up on the way, so I pretty much eliminated that possibility. It doesn't seem to be slow, and it seems as though the mirror up and shutter release are timed properly - I see a full image circle through the body when releasing the shutter at all speeds.</p><div></div>

[stephen t]

<p>(figured out how to attach an image to the post - duh)</p>

[stephen t]

<p>The more I look at that, the more I begin to suspect that the film wasn't wound tightly enough on the takeup spool, and when removed, got fogged?? I always, mostly, usually check the tightness after loading. </p>

[dave_thomas8]

<p>In its big brother, the SQ series, that is usually a problem in the light seal where the back opens. The sharply defined edge on one side and softer, fuzzier edge on the opposite is characteristic. The light is hitting the film ahead of the frame in position for a shot (one reason the first frame might escape the problem). As with most light leaks, it is also dependent on intensity and angle of light hitting the camera (and how quickly one winds and shoots).</p>

<p>Below the middle <a href="http://www.pbase.com/dw_thomas/sqgear">of this gallery</a> is an image "Oh My Back!" followed by several images of the seals in an SQ back. I rashly assume the ETR series is similar in construction. The seals are -- or were -- foam that has not fared well with time. I purchased one used back for my SQ-A where so little was left of one of the seals it did not appear there had ever been one.</p>

[stephen t]

<p>Dave, thanks. Not being familiar with the SQ, thanks to Mike Butkus I now have a manual for one and have compared the backs with the ETR. What you say makes a lot of sense. <br>

I'm going in the darkroom, going to remove the loaded film from the ETRS, place the film holder in my darkbox, and do some more work on adding light seals. I'll let you know how it works out.</p>

[dave_thomas8]

<p>Good luck Stephen! I might add that I would tend to rule out a mirror or shutter problem in this case because the pattern extends out into the rebate, meaning the film was not behind the frame mask when lightstruck. (And with a loosely wound roll I would expect to see a pattern more erratic and raggy on both edges and possibly not across the whole width.)</p>

<p>Replacing the seals is a bit tedious and fiddly, but I have managed to fix the problems I had with the SQ series backs. I haven't dealt with a dark slide seal yet, but no doubt I'll eventually get a chance! :)</p>

[User_502260]

<p>You can shoot a test roll by loading the film and then taping over all of the places that light could leak in. If no leaks show up then you know the light is getting in somewhere. I have been very lucky with my Bronica backs (ETR/SQ/GS-1) but one 6X7 120 back for the GS-1s seems to have a leak along the slot where the dark slide goes in. My repairman does not know where to get the material needed to fix this so I have put that back aside for now. </p>

[ondebanks]

<blockquote>

<p>I might add that I would tend to rule out a mirror or shutter problem in this case because the pattern extends out into the rebate, meaning the film was not behind the frame mask when lightstruck. (And with a loosely wound roll I would expect to see a pattern more erratic and raggy on both edges and possibly not across the whole width.)</p>

</blockquote>

<p>Dave is on the money with both these deductions. Light has struck the film from the rear of the camera, not the front; and it has struck when that area of the film was unrolled. Check <a href="/medium-format-photography-forum/00d9Sz">this recent Mamiya 645 thread </a>with the same type of problem.</p>