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  1. #21
    holmburgers's Avatar
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    You're misconstruing what I mean by "understanding". I'm talking about the science Loris, not the art.

    I know full well that this kind of analysis has little bearing on the production of a beautiful print, but I think it's really silly to suggest that by being curious about it, and spending some effort to figure it out, that it's going to be detrimental to the right side of my brain!

    *harumph*

  2. #22

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    Ok, just tell me how you're going to *USE* the information you're craving for then... (And please, use both sides of your brain!)

  3. #23
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    Quote Originally Posted by holmburgers View Post
    ...Also, we can say, well Vaughn's tissue requires 250 mJ/cm², and Loris' only requires 175... and ask why is that? Right now our only option is to say, well, I expose it from for 20 minutes from 3 feet away from 24 black-lights under a contact frame with 1/4" soda-lime glass and the relative humidity is always 60% and behind the bulbs I've sprayed Krylon's metallic luster paint which has a reflectance of about....
    aaggh!!! and harumph!!!!

    I think Sandy King has done some comparisons of different light sources that might help up get in the ballpark.

    But one even has to take into consideration the heat generated by the bulbs and the resulting temperature of the pigmented gelatin during the exposure as well as all the other factors I gave earlier. I just have a feeling that all these variables would make knowing the exact UV output of the light source to be of little practical use. Sort of like wanting to know one's air speed after a wing has fallen off.

    But it would be a nice thing to know why my tissue seems to take one to two stops more exposure than just about everyone else's (probably my low pigment concentration, though). But my exposure under a 750W Merc Vapor bulb is about 90 minutes (about 12" from the neg), while Howard's is 6 minutes under a 1000W "multi spectrum" lamp at 21" from the neg! That is some difference!
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  4. #24

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    Quote Originally Posted by Vaughn View Post
    ...
    all these variables would make knowing the exact UV output of the light source to be of little practical use
    ...
    And vice versa, the mJ/cm2 sensitivity / energy requirement figure which has been worked out exactly, will be ONLY meaningful within the context / exact conditions of the tester - NOT someone else... That would be - if you like - bogus science!

  5. #25
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    The only baseline the "units" on my NuArc have are to themselves.

  6. #26
    holmburgers's Avatar
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    I think it's an interesting question at the very least, and despite that it may appear to be a case of barking up the wrong tree, I think it's garnered undue razzing.

    If I can say that my tissue needs X mJ/cm² at normal sensitization; then everytime I encounter a new light-source, a new day where the sun or weather is different, I can take a reading (or several readings throughout my exposure) and multiply that number (mW/cm²) by the number of seconds to get mJ/cm².

    How hard is that?!?

    Then I have a specific target number that I'm striving for everytime. The sun has become my NuArc!

    Assuming outright that this isn't worth investigating, I think, is somewhat presumptuous. I can understand your positionthough; I'm sure it's irritating to see an under-experienced newbie putting the cart before the horse....

    Well my horse and I are perfectly happy in this arrangement!

  7. #27
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    I am sorry if I gave the impression that I was razzing you in any way. Just had a different opinion on the info's usefulness in comparing units of UV energy between different practioneers of carbon printing.

    I don't care where you put the horse, but you it seems that you have tried to change horses in mid-steam (going from using the values to compare the exposure times of different practioneers to comparing it to only one's own tissues.)

    I can see the usefulness when making one's own tissue. So it sounds like you need a UV meter -- and I guess with such a meter, one would have to assume that the the proportion of the various sections of the UV spectrum remain constant -- if the meter reads UVA, UVB and/or UVC, then hopefully the amount of the UVA (which is what we mainly use to expose with) stays proportionally the same relative to UVB and UVC. Otherwise one is not measuring what actually the material is sensitive to and one might as well use one of the cheap UV "meters" that warns one about sunburning potential -- accruacy will not be needed because one would not be measuring what one is using.

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

  8. #28
    holmburgers's Avatar
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    This meter (Solartech Model 5.0) measure UVA/UVB and has a peak sensitivity of 390nm (IIRC).

    No Vaugh, you weren't doing the razzing I was referring to...

    Ultimately I'm going to try to apply it to my own tissues of course, but trying to get some sense of other people's tissues only seems natural. There will be 2 limits; a tissue that requires the most UV and one that requires the least. I'd like to know what the spread is.

    The many questions & concerns perfectly highlight why doing a bit of investigation with a UV meter is needed; at the very least, to find some answers for them.

    Last time I take advice from Robert Frost...

  9. #29
    Nicholas Lindan's Avatar
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    Quote Originally Posted by Vaughn View Post
    ...my exposure under a 750W Merc Vapor bulb is about 90 minutes ... Howard's is 6 minutes under a 1000W "multi spectrum" lamp
    Graphic arts metal halide arc lamps are specific to the type of material being exposed. Using the wrong lamp can result in long exposure times. The metal halide HID lamps for graphic arts/UV curing have special dopants added to produce light at wavelengths that are optimum for a particular material. Iron-doped lamps emit heavily in the 350-400nM spectrum and may be a good match to dichromated gelatine which responds best to 360-375nM. Indium and gallium doped HID lamps produce most of their output in the 400 - 450nM range and may not be a good choice.

    If the mercury lamp you are using is made for general lighting then it is probably doped to produce most of its light in the visible spectrum and as little as possible in the UV.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  10. #30

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    Holmburgers, I wish you were paying a little more attention to what people say... I have little to add to what I have already written and to what Vaughn elegantly / subtly put in his last post; two simple sentence killed your nonsensical / pseudo-scientific approach I'm afraid. (I'm skeptical on the fact that you can notice that though; see #2 below...)

    I would suggest that you:
    1. Give some heed / consideration to what has been very clearly written before,
    2. Slow down your overcharged left brain and bring some of your sleeping right brain into play, (Believe me, you'll be amazed by the synergy you'll be getting!)
    3. I beg you, pour some glop and make a couple of test prints (as little as this will suffice to light the bulb - about what we're trying to explain to you - in your head!) before writing again; at least then you'll have an idea on what you're talking about. (Revisit #1 here...) I'm sorry but you really don't have a clue, and that's clear as crystal...

    I won't continue to this foolery anymore; it got unnecessarily personal / ad hominem (and I'm not helping here, I must admit!), w/o providing any useful / meaningful information to others (been there, done that, and got my lesson; I absolutely have no intention to repeat...) - that's the actual purpose of this forum, right?

    Anyway, good luck to you!

    P.S. For sake of making you happy/comfortable: You did good by purchasing that UV meter, really... (Can't wait to read about your precious results / conclusions that you're going to generously share with us later!)

    P.S. #2. Since I was accused of razzing, I thought I would better do justice to that...
    Last edited by Loris Medici; 02-10-2012 at 04:23 PM. Click to view previous post history. Reason: Added the P.S. #2.

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