Limiting light output...

Discussion in 'Contact Printing' started by DougGrosjean, Aug 22, 2007.

  1. DougGrosjean

    DougGrosjean Member

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    Hi all,

    I've started playing with contact printing my 4x5 negs for fun. My printing experience (was) extremely limited, but after some time I got good output and am pleased.

    Except for one thing....

    My bulb is a 15w bulb, in a desk lamp with a rounded cone (sort of a parabola shape), about 3' above the negative.

    The printing paper suggests a 7.5w bulb at least 4' above the paper, but I couldn't find anything quite that week.

    End result:
    My exposure time on thin negs is about 1s, dense negs about 5s. I'd like to slow the process down, so that even the thin negs require several seconds of exposure, so that I could burn and dodge.

    Question:
    Any ideas on a cheap simple way to dim the light? I was thinking nuetral density filter - perhaps a tinted shield from a motorcycle helmet, cut to shape and taped in place on the lamp (since the exposure will be short).

    Any better ideas before I spend money?
     
  2. Nick Zentena

    Nick Zentena Member

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    Move the bulb. Say lift it to 4.5 feet.

    Remember light increases/decreases with the square of distance or something like that -)
     
  3. DougGrosjean

    DougGrosjean Member

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    I'll try that first. Just gotta think on how... it's in the bathroom, on a countertop, so I'll have to put a box under it or something.

    Thanks.
     
  4. DWThomas

    DWThomas Subscriber

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    I know you can buy 7.5 W bulbs with a standard household screw base, that would give you a little less light. Years ago I did some contacts using a radio pilot light type bulb hooked to an old toy train transformer from my (massive) junk collection -- that makes it almost point source.

    (Of course I am a compulsive tinkerer. :D)

    DaveT
     
  5. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Weston had his bulb on a peg board so it could be set at different heights (you could even space them by stops if you wanted), and he had some cloth over the bulb, which must have acted both to diffuse the light and reduce output.

    If it wouldn't generate too much heat and present a fire hazard, you could put one or more layers of cloth or paper under the bulb.
     
  6. David Brown

    David Brown Subscriber

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    7.5W bulbs are available. If the "desk lamp" in plugged into an outlet, you could also buy a dimmer, perhaps incorporated into an extention cord, that would give you quite a bit of control over the level of light.
     
  7. MattKing

    MattKing Subscriber

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    Have you tried bouncing the light off the ceiling?

    Matt
     
  8. DougGrosjean

    DougGrosjean Member

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    All,

    Thanks for the ideas.

    Going to try, in order:

    Bouncing light off ceiling because it's easiest. If that doesn't work, then:

    Find a 7.5w bulb. If that doesn't work, then:

    A variant of David A. Goldfarb's idea... I'll try to restrict the light by making an aperture. I know the opening size of the existing cone, I can calc out a circle with half the area and thus half the light. Since we're talking just seconds, and the 15w bulb doesn't generate much heat, it should be OK.

    Thanks!
     
  9. John Curran

    John Curran Member

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    Doug,
    I had the same problem w/my omega B-600. I shot some B&W 4x5 exposures of a flat white wall using the negatives to create a neutral density filter and cut and inserted the 'filter' in the enlarger. Exposure times are now up around 4 sec for Ilford MG IV satin and about 8 sec for MG wartmtone glossies.

    best regards

    john
     
  10. DougGrosjean

    DougGrosjean Member

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    Hi all,

    John - good idea.

    But bouncing the 15w light off the ceiling worked like a charm. Negatives that are very dense (very overexposed winter scenes) around 20s, normal density negs about 5s, thin negs around 1s.

    Thanks, all - good to have reasonable times & control.
     
  11. Scott Peters

    Scott Peters Member

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    You can get a roll of neutral density filter film for relatively cheap...I think I paid $6 and you can either place it over the contact frame. Makes dodging and burning tougher. If you have a cone or shade around the bulb, you could cut a piece of the film and attach it to the cone/shade/reflector. Raising the buld is a good idea too. Make sure you get even light on the neg.
     
  12. sanking

    sanking Member

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    When I print silver I use a 7.5 watt bulb in a small reflector. At the base of the reflector I attached a small frame that allows placement of 6X6" ND filters. You could also use VC filters in the frame.

    Sandy King
     
  13. DougGrosjean

    DougGrosjean Member

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    Another update.

    I turned the light source 180d and bounced it off the ceiling, and that improved things a bunch - but my development times were still very short compared to the makers reccomendations. About 15s instead of 60s, with an exposure of around 20s.

    So I tried another tack to limit light. Went into my son's room, and found an orange frisbee from Hooters. Put that over the 15W light (still shining upward off the ceiling), and ran some prints.

    Success! Exposure times on a negative with nice density and tones is now around 20s, with dev. times around 60s. The blacks are *black* now, whites remain white. Contrast is far better than I had been getting, the prints really pop and the tones are nice and crisp rather than muddy and low contrast.

    I think I was overexposing, and then compensating for that with short development times, and not allowing the blacks to ripen properly; if that makes sense.
     
  14. tommy5c

    tommy5c Member

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    hooray for Hooters!! and their wonderful Frisbees!!
     
  15. bliorg

    bliorg Member

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    I bought a rheostat, an outlet, some wire, and a box. Made a dimmable outlet for about $8. Plug my light source into it, and I can dial in the proper light intensity.

    Easy peasy.
     
  16. Joe VanCleave

    Joe VanCleave Member

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    S11-Style 7.5 watt frosted bulb

    I've been using this 7.5 watt, standard base frosted bulb for contact printing.

    One benefit of a white frosted bulb is that the color is neutral; a red colored frisbee may work, but I would be concerned about it's effect on contrast, or how it affects your ability to control contrast.

    ~Joe