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  1. #31
    bobwysiwyg's Avatar
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    Martin, I too have noticed the very brief delay in the start-up of LED's. I attribute it to the need to convert house current down to what is needed by the LED architecture. Nothing like the annoying delay (for me) of CFL's but not the instantaneous "on" exhibited by incandescents. They, LED's, are after all small electronic packages. In everyday life, the brief delay is barely noticeable.
    WYSIWYG - At least that's my goal.

    Portfolio-http://apug.org/forums/portfolios.php?u=25518

  2. #32
    AgX
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    Quote Originally Posted by MartinP View Post
    Apart from the location of the illumination with respect to the condenser(s) of a black-and-white enlarger, the other question-mark would be about the spectrum of the colour temperature of these lamps and whether there are any peaks or troughs compared to incandescent lamps. The only thing to do is try them and see I suppose!
    Meanwhile there are (expensive) LED cinematographic lights ready to substitute the classic incandescand or HMI fresnel light.

  3. #33

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    Maybe I'm going a bit out of topic, but reading about people trying LED bulbs made me think about one point that is not so clear for me. Does one need to consider if the distance between bulb and condenser change, compared to the original design? Is this parameter very important, I mean does the distance bulb-condenser have to be fixed and what happens if it changes?

  4. #34
    AgX
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    With every point light-source when employed in a condensor lighting system the distances lamp/condenser and condenser/lens have to adjusted.

  5. #35
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    I might add: For every exposure for proper light balance.
    Richard

    Why are there no speaker jacks on a stereo camera?

  6. #36
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    Should have said with every change in enlargement factor.
    Richard

    Why are there no speaker jacks on a stereo camera?

  7. #37
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    I'll report back on print results as soon as I have them, depending on when I next get some darkroom time. Hopefully that'll be this week, finished making a lamp holder box of sorts yesterday.

    On my enlarger (Beseler 23CII) moving the bulb too far up or down will cause light falloff, unevenness and formation of dark rings at the edges. There's some leeway here but I wouldn't want it too far from spec.

    This particular LED bulb appears to turn on and off about as quickly as an incandescent does. I've heard of some of them having noticeable on/off times, possibly because of circuitry designed to smooth out the AC voltage supply. Perhaps the cheaper bulb skimps on that as a cost-cutting measure, which works in my favor here. Also, it claims to be OK for use in enclosed fixtures, which can't hurt.

  8. #38

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    Quote Originally Posted by Paul Glover View Post
    I'll report back on print results as soon as I have them, depending on when I next get some darkroom time. Hopefully that'll be this week, finished making a lamp holder box of sorts yesterday.

    On my enlarger (Beseler 23CII) moving the bulb too far up or down will cause light falloff, unevenness and formation of dark rings at the edges. There's some leeway here but I wouldn't want it too far from spec.

    This particular LED bulb appears to turn on and off about as quickly as an incandescent does. I've heard of some of them having noticeable on/off times, possibly because of circuitry designed to smooth out the AC voltage supply. Perhaps the cheaper bulb skimps on that as a cost-cutting measure, which works in my favor here. Also, it claims to be OK for use in enclosed fixtures, which can't hurt.
    Sounds great! Looking forward to it. Im very interested to see if the contrast is affected on VC paper. In your previous post you said you had to exclude many LED bulbs because of light unevenness. Im curious on how exactly you selected the one you are testing. Is it possible to visually identify hotspots in the light source, when projected to the baseboard?

  9. #39
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    Quote Originally Posted by mauro35 View Post
    Sounds great! Looking forward to it. Im very interested to see if the contrast is affected on VC paper. In your previous post you said you had to exclude many LED bulbs because of light unevenness. Im curious on how exactly you selected the one you are testing. Is it possible to visually identify hotspots in the light source, when projected to the baseboard?
    I wrote up the process of finding a bulb and initial tests, with some photos, at http://www.paulglover.net/20140108-o...possibilities/

    TL;DR version: I ruled out any of the bulbs which look like mood lighting for a spaceship or otherwise had designs which weren't going to present an unbroken area of light on the end, where it's needed. Some of these things are pretty wacky looking! Then looked online for photos of the bulbs lit up. Read reviews to see what else might be a problem. That narrowed it down to the Utilitech.

    At this point I walked into my local Lowes and by good luck they had a dimmer demonstration set up using one. To my eye it looked like there were no obvious problems with the way it lit, so I grabbed one.

    Right now it's all visual assessment. I think it looks OK compared to the PH140 but I don't 100% trust it without some sort of testing on paper.

  10. #40

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    Very nice web page! Waiting for part 2...I also found a cheap LED bulb which has actually a very similar shape as the PH-140 lamp and the same E26/E27 mount. Its a Philips 25 W equivalent:

    http://www.ledwholesale.eu/philips_c...27_p45_fr_1337

    Of course the power output is significantly lower compared to the 75W incandescent, so that might be a big limitation. But the light looks really even and of the same color temperature. Trying to look at the same negative projected on the baseboard I can only notice visually a reduction of intensity (obviously) with the LED, but no shadows or hot spots.

    Cant do a real life test yet, cause Im waiting for my photopaper to be shipped.
    Last edited by mauro35; 01-15-2014 at 04:28 AM. Click to view previous post history.

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