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  1. #1
    Greg Davis's Avatar
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    Film Fogging with 10 stop ND filter

    I am trying a long exposure using a Kodak 3.0 ND filter (10 stops) and constantly get excessive film fogging. It is a 4x5 camera and one of the Nikon gel filter holders that screws into the lens, so there isn't a gap between filter and lens for light to leak in. I am using a compendium shade to keep flare light from striking the filter, but I still get a lot of fog. The edges of the film are clear like normal, but the shadows are dense with no information. If they had any, I would say that my reciprocity correction was too generous and I was getting overexposure, but the shadows are featureless yet overly dense. Any thoughts? Would putting the filter behind the lens help perhaps?
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  2. #2
    cliveh's Avatar
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    Are you sure the fogging is a result of the ND filter, as it may be due to a number of other factors.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

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    Shawn Dougherty's Avatar
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    Hmmmm. Interesting problem. You say that you are using a bellows hood. Are you extending it to the maximum without vignetting the image? If not it COULD be excessive flare from the big image circle...

    Otherwise everything you're saying makes sense to me. Filters behind the lens invite many other problems...

  4. #4
    alienmeatsack's Avatar
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    In my experience, any time you extend the exposure on any camera type well beyond the normal times, the little leaks and issues tend to come up because of the extra light that's being introduced.

    I would try a test exposure in a controlled environment with little to no extra light anywhere around the camera, and the only light being what is focused on the test subject. This should let you know if it's a leak somewhere that is allowing extra light in vs the ND filter itself somehow causing the leak I'd think.

    I had a similar problem with a pinhole lens on one of my cameras - the extra exposure time revealed some leaks between the lens and the body that were not visible during normal exposure times.

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    Shawn Dougherty's Avatar
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    That's a good point. Did you wrap the camera in your dark cloth during the exposure?

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    I have used that same gel filter and it worked OK. Low contrast, but no film fog.

  7. #7
    Greg Davis's Avatar
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    It is acting like excessive base fog, but only in the image area, not in the edges. It doesn't appear like a directional light leak. As far as a controlled lighting situation, it is, I am in the studio not outdoors.
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    Shawn Dougherty's Avatar
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    That does make it sound like some sort of flare issue... maybe...

    You might try reaching out to Bill Schwab or one of the other fellows who have been shooting long time exposures for years (and don't follow the apug threads that closely).

  9. #9
    ic-racer's Avatar
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    Do a long 'exposure' with the shutter closed and see what happens. That way you can tell the difference between fogging from 'flare' light that came through the lens vs light leaking in through the bellows or around the lensboard etc.

  10. #10
    RalphLambrecht's Avatar
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    Quote Originally Posted by Greg Davis View Post
    I am trying a long exposure using a Kodak 3.0 ND filter (10 stops) and constantly get excessive film fogging. It is a 4x5 camera and one of the Nikon gel filter holders that screws into the lens, so there isn't a gap between filter and lens for light to leak in. I am using a compendium shade to keep flare light from striking the filter, but I still get a lot of fog. The edges of the film are clear like normal, but the shadows are dense with no information. If they had any, I would say that my reciprocity correction was too generous and I was getting overexposure, but the shadows are featureless yet overly dense. Any thoughts? Would putting the filter behind the lens help perhaps?
    you can check your camera for light leaks by placing a small light into it and obseving it from all sides in a daek room
    where light leaks show up immediately.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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