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  1. #31
    cliveh's Avatar
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    See my thread Determining Exposure Time.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  2. #32
    Vaughn's Avatar
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    Quote Originally Posted by cliveh View Post
    See my thread Determining Exposure Time.
    For those who do not wish to search:

    Determining Exposure Time

    I love the Brassai method of determining exposure time, as he claimed to time his night shots by smoking cigarettes.
    “To gauge my shutter time, I would smoke cigarettes – a Gauloise for a certain light, a Boyard if it was darker.” Do others have a similar method of gauging long exposures? I have sometimes exposed salt prints by the time it takes to make and drink a cup of tea.
    Night exposures certainly have that sort of leeway! And with my long carbon exposures certainly have many minutes leeway where it makes no difference if I expose at 90 minutes or 95 minutes!

    I wonder what kind of light he would have smoked a cigarette de chanvre for.

    Vaughn
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  3. #33
    Bill Burk's Avatar
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    I had one of these in the prepress dept...

    http://www.ebay.com/itm/UVP-BLAK-RAY...item4aaf9c8310

    The way I used it was to turn on the lights in the photopolymer platemaker, a unit with tightly spaced rows of fluorescent bulbs, maybe a dozen 48 inch bulbs. They weren't blacklight, because they put out plenty of regular light, but they were special bulbs that put out a lot of UV. I'd touch the four bumps of the sensor against each bulb and run from one end to the other and watch the needle. If any bulb was dying, you'd never know by the white light because the bulb would look plenty bright, but the needle would take quite a dive.

    So your meter, you can use it to make sure your light is performing as it was the last time you used it. Or you can judge the UV of daylight. Or you can go shopping for UV light sources and pick the source that gets you the highest readings.

    So even though I always used material with a consistent response to light, I never "calibrated" any device in the shop to a particular setting based on a published speed of a plate or film. I always burned a Stouffer wedge with each plate - and adjusted exposure based on the results on the test strip. Nobody in the shop ever dared make even one plate or film without a step wedge on it.

  4. #34
    Vaughn's Avatar
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    Bill -- those were probably BL's -- just like the blacklight bulbs (BLB), but without the visible light filter built inside the tube (which makes them a bit more expensive than the BL's).
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  5. #35
    Bill Burk's Avatar
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    Quote Originally Posted by Vaughn View Post
    Bill -- those were probably BL's -- just like the blacklight bulbs (BLB), but without the visible light filter built inside the tube (which makes them a bit more expensive than the BL's).
    Sounds right, they burn cooler too. Overall, I think it was a low-priced unit but good enough for the photopolymer plates.

    Other exposure units in the shop and platemakers had much better point source lights.

  6. #36
    Vaughn's Avatar
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    That makes sense -- the energy of the white light would just be absorbed by the tube instead of shining through. I was not satisfied with the softer carbon prints (contrast and sharpness) I got with BL tubes compared to the sort-of point sources -- Merc vapor lamp in my case.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  7. #37

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    You lost me there Vaughn. How would BL bulbs create a softer print than a point light source like a MH or merc vapor bulb?
    Technological society has succeeded in multiplying the opportunities for pleasure, but it has great difficulty in generating joy. Pope Paul VI

    So, I think the "greats" were true to their visions, once their visions no longer sucked. Ralph Barker 12/2004

  8. #38
    Vaughn's Avatar
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    BL (and BLB) bulbs are a very diffuse light source. It is like enlargers for silver gelatin printing where a diffusion enlarger will give a less sharp and less contrasty print than a condenser enlarger (everything else being equal).

    A carbon emulsion is very thick (relative to silver gelatin) and if you imagine a small dot sitting on the top of a carbon tissue with light from a diffuse light source, the shadow cast by that dot ends up spread over a significant distance by light hitting it at a very shallow angle. See the diagram below (okay...it is a pretty rough drawing!LOL!)

    But a point source (or close to it) the dot's shadow is straight down into the carbon emulsion with very little spreading.

    I made a palladium print of Friday and accidently printed the neg upside down under a bank of BL tubes. Just the thickness of the film base was enough to make the image mush. Same idea.

    Vaughn
    Attached Thumbnails Attached Thumbnails Dot.jpg  
    Last edited by Vaughn; 02-12-2012 at 10:08 PM. Click to view previous post history.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  9. #39
    mdm
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    I find my Nuarc to vary with the ambient temperature. 10C = fast exposure, high contrast underexposed, 15C = normal, 20C = very slow, low contrast and over exposed. So to get reasonable results I have to use different dichromate percentages and slightly alter exposure according to temperature. Took a while to work out.

    I adjusted the spiral thing on the integrator to allow the max light to enter in an attempt to even out its inconsitencies but that made no difference except to how fast it counts. The perspex cover on the integrator has cracks from time and exposure to UV so I have considered removing it or replacing it with something else.

  10. #40
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    Quote Originally Posted by Loris Medici View Post
    Holmburgers, I wish you were paying a little more attention to what people say...
    Loris, this has gone too far.

    I'm sorry that you find me so reprehensible.

    "nonsensical / pseudo-scientific" and "...as little as this will suffice to light the bulb - about what we're trying to explain to you - in your head!", plus, "I'm sorry but you really don't have a clue, and that's clear as crystal..." and so on.

    You've made all the worst assumptions possible, instead of giving me even the slightest benefit of the doubt.
    Last edited by holmburgers; 02-13-2012 at 03:15 PM. Click to view previous post history. Reason: edited signficantly

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