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Thread: Nude

  1. #2001

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    Re: Nude

    Quote Originally Posted by Leigh View Post
    However, given the amount of power being discharged it certainly is possible.
    Maybe, or maybe not - the pressure inside flash tubes is quite low. We'd have to find some data to the pressures used and the heat distribution in the gas caused by the discharge to figure out whether the pressure build-up during discharge gets anywhere close to critical. Personally I rather doubt it rises much above atmospheric pressure, given the thin glass walls on many of the tubes I've handled and that they seem to im- rather than explode as the worst possible failure mode.

    HMI is quite another beast - with a tube under pressure to start with and continuous power at a scale not that far off what a flash does for its 1/2000s of burn (every five seconds as the heaviest use scenario possible). And even then, it is not that dangerous, security procedures on the fly sheets for my HMIs don't go beyond recommending goggles for lamp changes, and the worst I've seen from HMI in practice were cut fingers. Now Xenon short arc is the real bomb, under enough pressure even when cold that projectionists don something that looks like a bomb defusing squad body armour whenever they have to do a lamp change.

    The Pyrex covers on higher quality flash heads doubled as a protector against flash tube and halogen breakage, but their primary purpose was to reduce the difference between the flash and halogen light distribution.
    Last edited by Sevo; 20-Feb-2013 at 11:55.

  2. #2002

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    Re: Nude

    Photo flash lamps do on occasion burst during operation as pretty much all photography lamps I know are under positive pressure (during operation). I've seen a few returns during customer's development of power packs. Just the nature of limit testing. In most, if not all cases, flash lamp failure coincides with mechanical or electrical abuse or failure of the power supply system. Exceeding the life time significantly and ignoring the warning signs (missed flashes) puts one at risk of a (small) explosion. Glass domes, reflectors, grids or softboxes will all contain the debris without any issues. Open bulb operation (to maximize UV) can be problematic but only at very short distances. The loud "pop" is in most cases the scare thing. This said, there is no such thing as no risk in high energy flash applications (2400J and up)

    Sevo is right about the bulb failure aspects from HMI and cinema bubble xenon lamps. These have to be handle with protective gear, face shield and leather apron etc....

    As for the amount of UV in the light output of a flash lamps. There are many factors playing but it boils down to the envelope material choice for the flash lamps (soft glass, hard glass, doped quartz or pure quartz and possible color correction coatings) and the peak operating current in the lamp (higher = more UV)

    If in doubt, measure or chase down the specs ;-)

    For those that like to find out about some of the technicalities, below you'll find a link to an application note that explains some of the above in light of current densities and "glass" material selection. IF you have specific questions, PM me.


    http://www.excelitas.com/downloads/a...inal071004.pdf

  3. #2003
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Nude

    Quote Originally Posted by Sevo View Post
    Maybe, or maybe not - the pressure inside flash tubes is quite low. We'd have to find some data to the pressures used and the heat distribution in the gas caused by the discharge to figure out whether the pressure build-up during discharge gets anywhere close to critical.
    No we don't.

    Glass can shatter from thermal shock alone, without regard to pressure differential.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  4. #2004

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    Re: Nude

    Sorry to have started such an argument about glass, honestly I would at least have 1 diffusion panel for a wet plate image or I think the light would be too harsh.

    Secondly I've seen a guy on APUG who was experimenting with freeze motion wet plate, he had models frozen jumping in the air with no sign of movement telling me the shutter was at LEAST at 1/125 of a second...

    So it can be done... Somehow.

    Again I ask, can you PUSH wet plate?

    Lets get away from this glass bursting issue and back to nudes!

  5. #2005

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    Re: Nude

    Quote Originally Posted by StoneNYC View Post
    Lets get away from this glass bursting issue and back to nudes!
    indeed...

    Why not start a thread about the technical issued in wet plate? (if it isn't already there...)

  6. #2006

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    Re: Nude

    + 1

  7. #2007

    Re: Nude

    Another plate of Anastasia. I was originally disappointed with the arm placement on this one (hence I left it in the yard) but it has grown on me over time. And the unvarnished silver picked up bit of a nice patine through a couple rains.

    Ed Ross

  8. #2008

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    Re: Nude

    Quote Originally Posted by life_in_sepia View Post
    Another plate of Anastasia. I was originally disappointed with the arm placement on this one (hence I left it in the yard) but it has grown on me over time. And the unvarnished silver picked up bit of a nice patine through a couple rains.

    I just love the detail! It's amazing, how do you do it?! Haha is this a standard wet plate emulsion or something you've tweaked over time?

  9. #2009

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    Re: Nude

    Quote Originally Posted by gandolfi View Post
    indeed...

    Why not start a thread about the technical issued in wet plate? (if it isn't already there...)
    Done!

    http://www.largeformatphotography.in...d.php?t=100420

  10. #2010
    Peter De Smidt's Avatar
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    Re: Nude

    Ed, I like that one a lot. What didn't you like about the arm placement? The lack of seeing any hands? If so, that doesn't bother me at all here.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

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