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Thread: Stumped on cause of evident light "leak"

  1. #1

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    Stumped on cause of evident light "leak"

    I am stumped by the wedge of extra density shown here. Perhaps someone has some insight. Here are the circumstances.

    I took the Tachihara 4x5 out one afternoon to see what the interesting clouds and my orange 21 filter might do. I took 2 holders loaded with HP5. The camera was set up and remained stationary for all four exposures. I took my readings at the outset of the session and set the shutter speed and aperture, which also remained unchanged (1/60 at f/11 after the filter factor).

    Unsure of how fast the cloud changes might occur, I pulled the slide once the holder was seated and let the camera wait, with my dark cloth folded over the back and bellows, for up to perhaps 20 minutes before releasing the shutter on a given sheet. I had no watch, so I don’t know the intervals. The camera was in direct sun. This long interval naturally comes up for suspicion.

    I was facing west, a bit southerly. As you can see, the sun was high and to the left; it didn't get too frontal while I was out.

    Here's the real stumper for me: the same pattern appears in the same place on all sheets, though the density varies somewhat. Since it doesn't spread into the film margin behind the holder edge, it was caused in camera (my darkroom is properly dark anyway). The density is greater at the edge than toward the center where the wedge narrows and ends. I can see no way it could come from that side; holders were seated properly. The position, in camera, was upper right (looking at the back of the camera).

    Could it have come through the light trap in the holder the same way in all sheets? Unlikely, I think. The only guess I can make is some internal reflection from a surface inside the camera, but I can't figure out what it could possibly have been. The shape doesn’t look like a typical seating problem, and it's identical with both holders; nor does it look to me like any optical flare I've experienced in any format, and the sun was moving, so, were it the latter, presumably the flare position would have moved. Same for bellows, and that's one weird bellows leak, if it is one, especially with the dark cloth on top.

    I can repeat the circumstances generally, perhaps that's the only way to see if it's repeatable. Meanwhile, any insights?

    Click image for larger version. 

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    Philip Ulanowsky

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  2. #2
    Vaughn's Avatar
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    Re: Stumped on cause of evident light "leak"

    You need to to the old flashlight test -- pitch dark room, holder in camera, lens off, and stick a flashlight into the bellows to see if it lights up like a planetarium. Take a hard look around the film holder/camera back.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

  3. #3

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    Re: Stumped on cause of evident light "leak"

    You have to discover light leaks before they find your film. Unless you are very sure of the condition of your bellows, it should be checked frequently for leaks in the corners, especially the single layer construction type like Toyo.

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    Re: Stumped on cause of evident light "leak"

    Bellows, eh? Darkroom, here I come.
    Philip Ulanowsky

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  5. #5

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    Re: Stumped on cause of evident light "leak"

    Fully extend the bellows to it's slightly beyond max before doing the flash light test in a darkened room. Light leaky bellows are most common at the corners and frame joints.

    Bernice

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    Re: Stumped on cause of evident light "leak"

    Thanks, all for the advice to check the bellows. I found a few, tiny pinholes at the top corners of the of the left side, whence the sun was shining, and have repaired them with black acrylic paint. I can't imagine they caused the particular problem I had, though, as mentioned, the long time the film was uncovered in the camera before exposure seems by far the most likely culprit. But what's life without a few mysteries? Fortunately, this one was not encountered on photographs that mattered.
    Philip Ulanowsky

    Sine scientia ars nihil est. (Without science/knowledge, art is nothing.)
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  7. #7
    Maris Rusis's Avatar
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    Re: Stumped on cause of evident light "leak"

    I use a Tachihara 45GF camera and have seen the occasional light leak.
    The first step in field testing the problem is to use photographic paper in the holders - saves money.
    Then I put on a 300mm lens to stretch the bellows and shoot a portrait orientation outdoor scene in full sunlight.
    For the second shot I take the back off the camera and re-attach it upside down. The holder is loaded from the bottom up. Second sunny exposure is done.
    If the light leak is in the same place suspect the bellows.
    If the light leak moves to the other side suspect the fit between the camera back and the rear standard.
    So far all the light leaks in my 30 year old hard-working Tachihara are from corner pinholes in the bellows. I patch them with 3M type 850 black polyester tape.
    And I do the light bulb (cool running LED) in the bellows test in my darkroom before an extensive outdoor 4x5 shoot. No pinholes is good pinholes.
    Photography:first utterance. Sir John Herschel, 14 March 1839 at the Royal Society. "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..".

  8. #8
    Vaughn's Avatar
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    Re: Stumped on cause of evident light "leak"

    The light leak does not look like from the bellows anyway -- a little too direct from the side. Did you move the back around a little and holder in it to make sure there was no light shining through at any time?

    The other question would be it the leak appears under the same circumstances in the landscape position? The suggested test with photopaper is a good one also.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

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    Re: Stumped on cause of evident light "leak"

    Thank you, Maris and Vaughn. Better analysis than I had come up with, no surprise to me. I'll see what these tests yield, though I have no long lens, just a 210 and 135. I was using the 135 on the problem shots, which requires moving the back all the way forward and the back slightly towards it to allow infinity focus. Playing with the back positions may reveal the issue.
    Philip Ulanowsky

    Sine scientia ars nihil est. (Without science/knowledge, art is nothing.)
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  10. #10
    Vaughn's Avatar
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    Re: Stumped on cause of evident light "leak"

    I had a major light leak between the 4x5 camera back and the film back on a 3-month hitch-hike through New Zealand that ruined just about all my images. Hunt carefully and do not forget to check the underside.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

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