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Thread: Film sensitivity to GraLab clock glow

  1. #1
    Warren
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    Film sensitivity to GraLab clock glow

    How well does black and white film do (I'm using FP-4) when exposed to the faint green glow of a darkroom timer? My old GraLab's got a raucous buzzer, but not being able to see it is frustrating.
    Warren Kornberg

  2. #2

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    Re: Film sensitivity to GraLab clock glow

    If it is faint, as in the lights have been off for several minutes in the darkroom, it isn't generally a problem. If you put it on a shelf so that it cannot shine down directly into the sink or wherever you are handling film, it helps a lot. Fred Picker said it was exactly the right color to fog film, but who knows how he knew that?

    What I did was tape a big square flap of black flannel on top of mine. It can be flopped down over the front or folded and put up on the top exposing the dial. If I am using it, I lift the flap up after the lights are out. The dial will be very faint, but readable. Yes, they are wake-the-dead loud.

  3. #3

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    Re: Film sensitivity to GraLab clock glow

    It has never bothered my film. I keep it a few feet away. It has never bothered any paper either.

    These timers have been around for a long time

  4. #4
    Octogenarian
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    Re: Film sensitivity to GraLab clock glow

    To charge a GraLab's luminous dial to it's max., expose it to a florescent light for a few minutes. It will glow brighter for a longer period of time.

    Holding unexposed film directly against the brightly charged luminous dial for a few seconds will expose film and paper, but only at the point of contact.

    Otherwise, as long as you do not hold the light sensitive material directly against the luminous dial, it does not fog film or paper.

    If you're in doubt, test it for yourself. I did.

    (Ken, that statement is anecdotal. I have no scientific data to back up it up).

  5. #5
    jp's Avatar
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    Re: Film sensitivity to GraLab clock glow

    I throw a towel over mine while loading/unloading film.

    When processing film in a tray, it is on the other side of my darkroom (about 5-6' away) and I stand between the gralab and the trays. Never had a problem that way. Having it on a shelf above your sink is probably fine too, as but if you wear white it could illuminate you and fog the film.

    You could probably muffle or disconnect the buzzer if you wanted.

  6. #6
    David Brown bigdog's Avatar
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    Re: Film sensitivity to GraLab clock glow

    Quote Originally Posted by jp498 View Post
    You could probably muffle or disconnect the buzzer if you wanted.
    Later models had a volume control.

    Gralab now makes other models besides the 300 (167, 170, etc) that do not have the luminous dial, and may have one outlet rather than two (depending on model). I use one of those for film processing. They turn up on the auction site often enough if you look closely.

    http://www.gralab.com/products/details.asp?ID=3

  7. #7

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    Re: Film sensitivity to GraLab clock glow

    I had a GraLab timer on a shelf about three feet above and to the right of my developer tray. It never created a problem. Remember the inverse square law of light fall-off, under which the drop-off is inversely related to the square of the distance from the source (or something like that). So if you're three feet from the source you're receiving 1/9th the amount of light as you'd receive at the source (or something like that) and if you're four feet away you're receiving 1/16 (or something like that). Considering how weak that glow is from a Gralab timer to begin with, and considering that your film is surely at least a few feet away, it's highly unlikely that you'd have a problem.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  8. #8
    Moderator
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    Re: Film sensitivity to GraLab clock glow

    Mine was always on a shelf right above the sink, and I developed sheet film in hangers over open tanks. I never had a problem at all with FP4, or even with faster film.

    Rick "who wouldn't worry about it" Denney

  9. #9
    Vlad Soare's Avatar
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    Re: Film sensitivity to GraLab clock glow

    I use a radio alarm clock with luminous, dark green digits, like the one in the attached picture.
    I couldn't see any trace of fog whatsoever with HP5+ or TMY-2, which are more sensitive than FP4+.
    If this clock doesn't fog films, then neither will the Gralab. Don't worry about it.

  10. #10

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    Re: Film sensitivity to GraLab clock glow

    Quote Originally Posted by Gem Singer View Post
    (Ken, that statement is anecdotal. I have no scientific data to back up it up).
    Wizenheimer !

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