Film Fogging with 10 stop ND filter

Discussion in 'Exposure Discussion' started by Greg Davis, Nov 22, 2013.

  1. Greg Davis

    Greg Davis Subscriber

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    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?
     
  2. cliveh

    cliveh Subscriber

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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.
     
  3. Shawn Dougherty

    Shawn Dougherty Subscriber

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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. alienmeatsack

    alienmeatsack Member

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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.
     
  5. Shawn Dougherty

    Shawn Dougherty Subscriber

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    That's a good point. Did you wrap the camera in your dark cloth during the exposure?
     
  6. Hatchetman

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

    Greg Davis Subscriber

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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.
     
  8. Shawn Dougherty

    Shawn Dougherty Subscriber

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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. ic-racer

    ic-racer Member

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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. RalphLambrecht

    RalphLambrecht Subscriber

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    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.
     
  11. Andrew Moxom

    Andrew Moxom Subscriber

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    Measure the light through your filter to make sure it is a 10 stop filter. Some vary.
     
  12. Greg Davis

    Greg Davis Subscriber

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    But that would still give plain over or under exposure, not higher base fog in the image area.
     
  13. Ken Nadvornick

    Ken Nadvornick Subscriber

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    Yes. That's the ticket. Close off the system, isolate the variable in question, and test it under identical conditions.

    :smile:

    Ken
     
  14. Doremus Scudder

    Doremus Scudder Member

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    I'd suspect a bellows pinhole toward the front of the camera or light leak around the lensboard that is small enough that it doesn't have much effect at shorter exposure times. It would cause overall fogging of the negative at longer times, but not the part of the film rebate covered by the filmholder rails.

    I had a similar problem on a camera with bellows that appeared practically brand new. There were a couple of corners that had small holes. Fixed now :smile:

    Do the flashlight/lightbulb test of your bellows and lensboards to rule this out before looking elsewhere.

    Best,

    Doremus
     
  15. Greg Davis

    Greg Davis Subscriber

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    To follow up, I left a sheet exposed in the camera with the same set up and lighting as before, but did not open the shutter, letting any light leaks do their thing. I had zero fogging, which leads me back to the idea that it may be flare or glare off the filter itself. I will try extending the shade more or placing the filter inside the camera behind the lens next.
     
  16. Hatchetman

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    Interesting. I had the gel filter between a screw on filter (green) and the front of the lens.
     
  17. Doremus Scudder

    Doremus Scudder Member

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    Other possible causes of fogging are:

    Flare from internal reflections from a too-large image circle. This can be especially troublesome when there is a lot of bright areas just outside of the framed image. When using a compendium, extend it till it impinges on the ground-glass image then back off a bit for maximum effect.

    Light hitting the glass surface of the lens/filter itself from an oblique angle just outside the field of view. A well-adjusted compendium should fix this too.

    Do you have a coated ND filter? If not, then flare from light striking the filter surface will be worse. Still, I don't think this is your problem

    Do do the flashlight test just to be doubly sure. Not every pinhole shows up every time when simply exposing film. Extend the bellows to the max and check from every conceivable angle.

    And, are you really sure you are not just overexposing? A featureless shadow area overexposed will be a featureless denser area... In such cases, the negative will usually print well unless you have pushed the highlights way up onto the shoulder of the film curve. Check the near-shadow (e.g., Zone II and III) areas. If they have the detail you saw in your scene, then you have likely just overexposed, especially if the film rebate is clear (Zone 0).

    Keep us posted.

    Doremus
     
  18. Greg Davis

    Greg Davis Subscriber

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    It is definitely not plain overexposure. I have been doing this long enough to know what that looks like, and I took a very short exposure before hand to compare it to. I also checked again for pinholes and didn't see a single one. The elevated fog is killing the contrast. I am not using a multicoated filter, it is a Kodak gel filter, so I will try blocking out more lateral light.
     
  19. Shawn Dougherty

    Shawn Dougherty Subscriber

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    The combination of bellows flare and non-coated filter could certainly do it I would think. Let us know how it goes, Greg.
     
  20. Greg Davis

    Greg Davis Subscriber

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    Would a bag bellows help minimze bellows flare? I haven't tried that yet.
     
  21. Shawn Dougherty

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    Maybe some but the light is still in there... The best solution is to simply block the excess image circle. Since you already have the compendium hood you should be set.

    This is how I've always done it.
     
  22. Greg Davis

    Greg Davis Subscriber

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    Alright, to give an update: I listened to everybody's advice and tried a variety of fixes. I had success with pulling the compendium shade further out while also covering the camera with my dark cloth as added precaution. The negatives have increased contrast by eliminating the excess fog. The highlights are about the same density as before, but the shadows are reduced to a normal level. Thanks to everyone that chimed in and gave suggestions.
     
  23. alienmeatsack

    alienmeatsack Member

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    Glad you got it figured out. I kind of enjoy the troubleshooting process myself, but there's a point where you just want to take photos and not fuss with it. At least now you are past the fussing with it part and get back to taking photos.
     
  24. Shawn Dougherty

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    Excellent news, Greg.