Light leak has me stumped.

Discussion in 'Large Format' started by tom_johnston|4, Aug 14, 2005.

  1. I am having a strange light leak problem that has me stumped. It
    happens with my 8x10" Ansco/Agfa camera which was completely rebuilt
    before I bought it not long ago. The bellows are brand new and light-
    proof.

    There is no consistent pattern to the fogging. Approximately 1/2 of
    the sheets that I shoot are badly fogged. The other half are
    perfect. The camera is totally light proof which I have tested
    repeatedly by removing the lens board and looking into the camera
    while under a sealed dark cloth with inserted holders in both
    vertical and horizontal position and with the slides in and out and
    by checking from the back with back removed and operating the
    shutter.

    The fogging is different on each sheet which provides a clue but I
    have not been able to figure out what is causing the problem.
    Sometimes the entire sheet is fogged so badly that you cannot see the
    exposed image. Sometimes the fogging comes from one corner and fans
    out across part of the sheet and sometimes it comes from another
    corner. Sometimes the edges are clear and sometimes they are
    fogged. Sometimes part of the edges are clear while it is fogged in
    other areas. I even had one sheet that was fogged all over with
    the exception of a small relatively unfogged area several inches long
    and a couple inches wide near the middle of the sheet!

    The fact that sometimes the film is fogged on the edges would
    indicate that something is happening when the film is not loaded but,
    as I said, sometimes the edges are free of fog.

    I have been shooting large format for over 30 years and my loading
    and processing methods have never changed and I have never had a
    problem like this. Consistency is my watchword. The film is loaded
    and unloaded at the same time and under the same conditions. In the
    field, I use a changing bag and, when on the road, I sometimes load
    and unload film in a hotel bathroom with not only all lights off in
    the bathroom, but with the hotel room dark and at night so there is
    no possibility of leaks around the door. Besides, I have had this
    problem when the film was loaded in my normal changing bag which I
    also use to change all my 4x5" film which has never been fogged. I
    load both 4x5" and 8x10" film in the same sessions and under the same
    conditions.

    After first experiencing this problem, and after checking the camera
    carefully for light leaks, I suspected that the film holders may have
    not been seated totally. I found that it is possible for them to be
    seated incorrectly with this camera if care was not exercised but it
    is easy to see if they are inserted correctly once you are aware of
    this. In fact, I was confident that this was the problem. So the next
    time out, I very carefully and consciously checked to make sure they
    were seated properly. I thought for sure that the problem was
    solved and was very surprised to see fogging again. Just out of
    curiosity, I checked the camera with the lensboard removed and a
    holder inserted improperly but there were still no light leaks unless
    it was the holder was grossly unseated.

    My processing is the same as it has always been too although I
    recently switched from tray to line-tank processing for sheet film
    when processing large amounts of film. However, before I switched, I
    had the same erratic fogging with 8x10 processed in trays while all
    4x5" film was fine. In addition, about half the 8x10" sheets that I
    load and process together (in the same batch) are fogged while the
    other half is fine. For example, last week I processed 51 sheets of
    4x5" film that all came out fine as usual and then, in the same
    session, I processed 4 8x10 sheets in the same tanks with the same
    chemistry (replenished between batches). The four sheets were
    processed side-by-side in holders which where in a rack for lowering
    into the chemistry. Two sheets were perfect and two sheets were
    badly fogged. By badly, I mean that one was so bad that you could
    not see the image at all except for a small area in the middle of the
    film and the other was fogged so that you could only see the image on
    about 1/2 of the film. The fogging gradually faded as it neared the
    center of the film leaving about 1/3 of the sheet fog free. But,
    perhaps not coincidentally, the two good sheets were TMax100 and the
    two fogged sheets were TRI-X. Unfortunately, I can't remember if it
    was only TRI-X that came out bad in previous runs so it is possible,
    of course, that I simply have a bad batch of TRI-X but it would seem
    to me that the sheets would have fairly uniform fogging if that were
    the case and it wouldn't explain why sometimes the edges of the film
    are fogged and other times it's clear.

    Last time out, as an extra precaution, I left the camera covered with
    my very large dark cloth right up to the lens and removed and
    replaced the slides with the cloth covering the camera. There was no
    change. Half the film was still fogged. I always minimize the time
    that the dark slide is removed. It is the very last thing that I do
    before releasing the shutter with the exception of instances where I
    am waiting for a lull in a breeze to still moving grasses or plants
    in the foreground but that was not the case with the two bad sheets
    this time. The subject was static without changing light levels so
    the slides were only out long enough to make the exposure. I remove
    slides completely.

    One last thing. I have a variety of new and older (but sound) film
    holders but the film that fogged this time was in a brand new (never
    used once) Fidelity Elite holder. Both sheets were of the same
    subject, shot one after the other.

    What I know is:

    1) All my film, both 4x5" and 8x10" is loaded and processed under the
    same conditions and at the same time.

    2) I have never had light leaks of any kind ever in 4x5".

    3) I got fogging with a brand new holder.

    4) Testing from the back and front of the camera shows no light leaks
    at all. The fogging has occurred both before and after my lens
    received a CLA and total checkup from Grimes. Unfortunately, I only
    have one lens for 8x10" (14" Kodak Commercial Ektar).

    5) It is possible that I have only had this problem with TRI-X but,
    unfortunately, I can't remember if any TMax100 fogged previously.
    When this started happening, I thought it was an equipment problem
    (light leak) and just never thought about that (like a dummy).


    I have always prided myself in being able to logically analyze and
    diagnose technical problems of all kinds but this one really has me
    stumped. It's erratic. I would appreciate any ideas you can share.
    I apologize for the long post but I reviewed other threads on this
    topic and I wanted to answer questions that would be asked if I
    didn't go into detail.
     
  2. without reading every sentence in your post I wonder if you've ever randomly developed some sheets without passing them through the camera.

    <BR><BR>

    Also remember how Madame Curie discovered radioactivity. Perhaps it's not light that's doing it!<BR>
     
  3. Without googling it, I recall that film can get fogged from chemicals, heat, light, radiation and friction.
     
  4. It sure sounds like a non-light type problem. Got anything radioactive around, or have you broken a mercury thermometer at some point? I've read that mercury vapor will penetrate almost any packaging. Old ammunition with mercury based primers? Storage in some black plastic that's visibly opaque, but transmits UV and/or near IR? That's more common than you'd imagine. Any chance new film was x-rayed at some point during shipping? Can you successfully process roll film or 35mm? If you assume non-light type fogging, and ask enough questions, you'll either find something or rule it out!
     
  5. How are your holders?
     
  6. First let's see if there is a problem with the 8x10 film.<br>
    Load the 8x10 film holders (all of them) with 4x5 sheets (just tape the sheets in the holders). Then go out and expose all of the film. Develop the film and see if you get any light leaks.
    <p>
    Now let's check lens speeds.<br>
    Load up the 8x10s again with 4x5 (just to save costs) and expose one sheet for each shutter speed. Develop, yadda yadda yadda.
    <p>
    Give the camera another light test with film in the holders. Don't click the shutter, just let it get some sun in various positions.
     
  7. Tom- After shooting LF for 30 years, I'm sure you know to check the BACK side of your
    new lens boards? My first experience with an 8x10 yielded very much the same fogging.
    Same lens, incidentally. Then I saw my new shiny maple lens board, painted it black and
    no fog. Hope that's what is going on with yours.
     
  8. Is all of these fogged negatives from the same batch of film? Can it be possible that they somehow were fogged before you even handled the film?
     
  9. Two things can make it very hard to diagnose a problem: the problem is intermittant, or there are actually two problems.

    I suggest checking again the fit of the lensboard to the camera, and the fit of the
    shutter to the lensboard, both with the shutter closed. Past questions about light leaks that have stumped people have sometimes traced to mismounted lenses. As a last resort, you could get another lensboard and mount one of your 4x5 lenses.

    Fogging of the film under the film guides of the holder could happen in the camera if the fogging is heavy enough -- the light can bounce or pipe in the film.. But unless the fogging was extremely heavy, the exposure under the film guides would be less than outside.

    In previous problems like this people have suggested putting the camera in a dark room and putting a light bulb in the camera and looking from outside of the camera for a light leak. Obviously you don't want to overheat the bellows.
     
  10. I can't tell exactly how you've checked for light leaks in the bellows but as Michael suggests, the usual way is in a dark room with a flashlight moved around in the bellows while looking from the outside and paying particular attention to the corners. Pin holes towards the front of the bellows can cause intermitant leaks because they don't show up unless the bellows is extended beyond a certain point. I doubt that pin holes are the problem since you have only one lens and presumably extend the bellows more or less the same length every time with it but since you've tried everything else why not try this test too?

    Assuming this isn't the problem I'd buy another box of film and see if the problem possibly is with the film though it would be odd for some film in a box to be badly fogged and some not. Or you could just put some of your 4x5 film in an 8x10 holder and see what happens.

    Do you have an accessory of any kind that you use some of the time and not others that could be holding the camera back slightly open when it's used? A few years ago I put a bubble level on a camera back and started getting fogged film. Turned out the back edge of the level was ever so slightly hanging over the edge and preventing the back from fully closing. Again, it would be odd for something like this to be intermittant but you've ruled out the common causes of fogging so the only ones left are the odd balls.

    Given all you've said about your processing it doesn't sound as though the darkroom could be the problem so it has to either be the film or a light leak somewhere in the camera or holders. Someone else may have already suggested this one but try putting film in a holder, leave the holder out in bright light for a few minutes with the dark slide in, then process the film and see if it's completely clear. If it is then put film in a holder, put the holder in the camera, leave the dark slide in, fully extend the bellows, and put the camera in bright light for a few minutes, then process the film. If neither of these tests produces light leaks then you pretty well know know that it isn't a holder problem or a problem with the camera back, which at least narrows it down to the lens or lens board.

    The thing that's really odd about your problem apart from the fact that it's erratic is the extent of the fogging you describe. I've had light leaks from pin holes, from a hole in the lens board, from leaving the camera in direct sun light too long with the dark slide pulled, and from the bubble level problem mentioned above. In none of these situations did the leaks result in fogging to the extent you're getting it. The leaks showed up either as streaks across an otherwise fine negative or, in the case of the hole in the lens board, as ghost-like double images and mild fogging. That leads me to think that you have some bad film if it's all coming out of the same box though even then it would be odd for some sheets in the box to be bad and others not.
     
  11. Have you checked to make sure that you shutter is closing all the way? I have had shutters that appear to be closed but are actually not entirely closed leaving a pinhole opening where the blades come together.
     
  12. The strong flashlight -- with new batteries! -- is a great way to check for light leaks. Stick your face into the front of the camera while doing this with the light from outside, then reverse the process with the flashlight inside, and you outside. AND, make sure to tilt the light to all different angles, because sometimes the light will only be visible when tilted a certain way -- unlike room- or sun-light, which will penetrate because it's everywhere.

    Two more things not mentioned above:

    1) Try the flashlight test with filmholders in the back, and the darkslide removed. Try to see if the light is coming in through the light trap, where the darkslide goes into the holder.

    2) Try this: Take the back off the camera. Take off the ground glass panel. Then lay one of your new film holders into the back, then see if it rocks from one side to the other, or from one corner to the other. If it rocks, this would indicate that the back has warped.

    Also check and make sure that the groove in the back is deep enough for the ridge on the film holder. If the back has been refinished, the groove could well have been partially filled in with paint or varnish, preventing the ridge from fully seating into the groove, thus keeping the film holder from "mating" fully with the back.

    Different vintages of film holders have slight differences in the ridges on the outside, as well.

    The Ansco cameras are among the best built that I have ever seen, and amazingly consistent. So I doubt warping, but it's always possible, especially if the camera had been stored long-term in adverse conditions before rebuilding.

    Hope this helps.
     
  13. I skimmed over all the responses and could have missed if someone else suggested checking your lens board for leaks. I had a fogging problem a few years ago....the lens board had a pinhole in it, it can happen even with metal boards.
     
  14. Although this may sound strange -- I have had a problem with one of my cameras when using the polaroid back (it's heavy). The spring action of the back is not strong enough to always keep the Polaroid back against the holder, particularly when the camera is looking up. Since your's is an old camera -- and was recently rebuilt ... This could have just the elusive/erratic character you're describing.
     

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