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  1. #41
    Jesper's Avatar
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    If you are worried about light in your darkroom, just leave a paper out for a while with something covering part of it.
    Leave it for an hour and develop it. If there is a difference between the two parts you have a leak (that may or may not be a problem).
    If you can 't tell where it was covered everything is OK.

    APUG is a wonderful place.

  2. #42
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    Quote Originally Posted by Jesper View Post
    If you are worried about light in your darkroom, just leave a paper out for a while with something covering part of it.
    Leave it for an hour and develop it. If there is a difference between the two parts you have a leak (that may or may not be a problem).
    If you can 't tell where it was covered everything is OK.

    APUG is a wonderful place.
    Sorry, but this is not an entirely valid test. It ignores the threshold exposure paper needs to develop density. A slight modification makes this test much more sensitive and also more realistic.

    Expose the paper to what would develop to a light gray (threshold exposure) but don;t develop it yet, then leave it out with an opaque object placed on top of it for your maximum handling plus processing time (let's say) 10-15 minutes and process the paper normally.

    If you can't see any tell-tale signs of the object, now everything is OK.
    Regards

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

  3. #43
    Jesper's Avatar
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    The threshold is the reason for the extended time (one hour).
    In order to change state you need a certain number of photons of at least a certain level of energy (I am not going into exact numbers it varies between different materials).

    Let us say that you need ten units to change. That means that even though you have received nine nothing will be visible.
    This we perceive as the threshold.
    This is why you sometimes may need to preexpose film and paper but that is another story.

    In order to test the darkroom you can either, as Ralph suggests, use a prexposed paper and a shorter time or an unexposed paper for a long time. As long as the number of photons with the right energy is received there will be a change of state. With a preexposed paper you can take the level to nine and leave it out to see if it reaches number ten, or you can leave it out for a prolonged time starting at 0 to see if it reaches ten.

    There are a lot of methods, and most of them works.

  4. #44
    RalphLambrecht's Avatar
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    Quote Originally Posted by Jesper View Post
    The threshold is the reason for the extended time (one hour).
    In order to change state you need a certain number of photons of at least a certain level of energy (I am not going into exact numbers it varies between different materials).

    Let us say that you need ten units to change. That means that even though you have received nine nothing will be visible.
    This we perceive as the threshold.
    This is why you sometimes may need to preexpose film and paper but that is another story.

    In order to test the darkroom you can either, as Ralph suggests, use a prexposed paper and a shorter time or an unexposed paper for a long time. As long as the number of photons with the right energy is received there will be a change of state. With a preexposed paper you can take the level to nine and leave it out to see if it reaches number ten, or you can leave it out for a prolonged time starting at 0 to see if it reaches ten.

    There are a lot of methods, and most of them works.
    Are you considering the latency effect? This is not always a simple addition of photons. If your ten-photon minium was applied over too long of a time, some of their energy has already dissipated. A small initial preexposure is a more robust way to detect small additional exposures, in my opinion.
    Regards

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

  5. #45
    Jesper's Avatar
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    And that is why I tried to use "level" instead of photons.

  6. #46
    RalphLambrecht's Avatar
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    Quote Originally Posted by Jesper View Post
    And that is why I tried to use "level" instead of photons.
    Jesper

    My point is, very dim ambient lighting may be sufficiently weak to never create and exposure by itself. However, when added to the normal print exposure, it may increase print densities. To capture this fact, any safelight test must include a small pre-exposure, otherwise, it is unrealistic and may not show the detrimental effect of bad safelights, light leaks etc.
    Regards

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

  7. #47
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    Ralph, would this test be sensitive enough for film? Or should the test be done with film?
    Items for sale or trade at www.Camera35.com

  8. #48
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    Quote Originally Posted by fotch View Post
    Ralph, would this test be sensitive enough for film? Or should the test be done with film?
    Yes, but with film, I would expose the film in-camera to a Zone II (average measurement - 3 stops) and take it into the all-lights-off darkroom for 1/2 hour, while covering the film partially with an opaque object. Then develop normally and see if you see a difference. If not, the darkroom is sufficiently sealed against light leaks and safe for processing film in a tray.
    Regards

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

  9. #49
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    I have a curtainrod over the door, and pull a homemade black felt curtain past the door. It is extra long and drags along the floor a little, stopping light from coming in from the bottom, top, or sides of the door.

    It may not be necessary, but I also throw a towel over my gralab timer, as the numbers glow on it.

    Never had a problem with light damaged film or paper.

  10. #50
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    I put velco on the top of the door jam, on the outside of the door, and a strip of matching velcro on the blackout cloth to keep light from getting through the door.

    I put velco above the window, down the sides and on the bottom to hold the blackout cloth in my dry darkroom.

    For the wet darkroom, a large bathroom, I have a piece of wood with two hand grips and that is cut to the shape of the window. The wood has a much larger piece of blackout cloth attached to it. I place the wood with the blackout cloth into the window frame and use tape to attach the cloth to the walls.

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.



 

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