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Thread: Fumbling towards a correct exposure for Dry Plates

  1. #21

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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by Drew Bedo View Post
    ... If that is so, is any exposure compensation required to account for that? If a scene is metered for ISO 100 film (and I make an exposure on that film) , then adjust for the nominal ISO 1 speed of the dry plate , as discussed above,. . .is any further adjustment needed for the loss of half the spectrum?
    ... Can I assume that these are corrected enough to avoid a blue shift in focus (getting really modern "APO" lenses is off the table).
    Keep notes shooting and bracket on the side of overexposure a stop for the first shot or two. When you find the best E.I. for your plates, you can adjust your meter accordingly.

    Any modern lens is well color corrected into the blue. As far as UV goes: most lenses don't transmit light that is very far into the UV, it takes special glass to do that. It doesn't matter if your plates are sensitive to those wavelengths or not; they won't see them since they won't make it through the lens. Focusing should be fine. The "old timers" didn't bother with focus compensation...

    Doremus

  2. #22
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    Re: Fumbling towards a correct exposure for Dry Plates

    As an aside, does anyone know if rubylith (or some equivalent material) is available in Europe? I'd like to get some to cover a small window, but I don't even know where to start looking.
    "Be still and allow the mud to settle."

  3. #23

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    Re: Fumbling towards a correct exposure for Dry Plates

    When you solve Sunny Sixteen for a given film speed, it remains accurate down to ASA 1 and below. (With the exception of Doremus Scudder's post above, I've never actually seen speeds below ASA 1 given as an ASA number. When such speeds were common there were other scales.)

    Given f/16, shutter speed = 1 / rated film speed. That is to say, f/16 (on any lens at any time, barring filters, bad transmission of the lens optics and bellow factor) is the point at which the film speed is equal to the reciprocal of the shutter speed, under typical sunny conditions.

    Take the reciprocal of the film's original rated speed, or "box speed," 2, and you do indeed have 1/2 = 1/2 second. It's not necessary to count by stops when you know that the math works consistently. F/16th is just a convenient constant where the math works out, but believe me, it does, so I trust it implicitly.

    The way I would expose those plates, if I were dying to expose them at box speed, would probably be f/11 at 1/5th or f/16 at 1/2, but that's just me. Under most conditions, I would probably actually rate it @ ASA 1, giving an exposure of, say, f/16 at 1 second. Shooting half box speed gives you a valuable margin for error and makes printing/scanning easier in most cases. In Mississippi summer sunlight half box speed sometimes burns the neg a bit, and in the summer I shoot at box speed.

    For more convenient shooting, J. Lane does have Speed Plates rated @ ASA 25, which are what I have. Now I just need to figure out how to tray develop without a safelight, or else order a safelight!
    Last edited by RLangham; 12-Feb-2020 at 18:43. Reason: I accidentally wrote "f/16th" instead of f/16

  4. #24
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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by RLangham View Post
    When you solve Sunny Sixteen for a given film speed, it remains accurate down to ASA 1 and below. (With the exception of Doremus Scudder's post above, I've never actually seen speeds below ASA 1 given as an ASA number. When such speeds were common there were other scales.)

    Given f/16, shutter speed = 1 / rated film speed. That is to say, f/16 (on any lens at any time, barring filters, bad transmission of the lens optics and bellow factor) is the point at which the film speed is equal to the reciprocal of the shutter speed, under typical sunny conditions.



    For more convenient shooting, J. Lane does have Speed Plates rated @ ASA 25, which are what I have. Now I just need to figure out how to tray develop without a safelight, or else order a safelight!

    I've processed the ISO 25 plates under a very faint, indirect red light and things went well. As for "Sunny 16," right now on the Northern Plains it's "Sunny 22."


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  5. #25

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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by Two23 View Post
    I've processed the ISO 25 plates under a very faint, indirect red light and things went well. As for "Sunny 16," right now on the Northern Plains it's "Sunny 22."


    Kent in SD
    I need to just get one. I've wondered if I can very indirectly light my darkroom with an old "infrared" heater floodlamp I used for a lizard cage back in the day... I'd worry about it having blue or yellow in its spectrum and fouling things up, though. J. Lane himself told me that it would be a long shot, but that I should try it.

  6. #26
    Drew Bedo's Avatar
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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by Two23 View Post
    I've processed the ISO 25 plates under a very faint, indirect red light and things went well. As for "Sunny 16," right now on the Northern Plains it's "Sunny 22."


    Kent in SD
    ISO 25 dry plates? Can you direct me to a source?
    Drew Bedo
    www.quietlightphoto.com
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

  7. #27
    Drew Bedo's Avatar
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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by RLangham View Post
    When you solve Sunny Sixteen for a given film speed, it remains accurate down to ASA 1 and below. (With the exception of Doremus Scudder's post above, I've never actually seen speeds below ASA 1 given as an ASA number. When such speeds were common there were other scales.)
    Thanks, and the rest of your post is an excellent explanation of the Sunny sixteen rule.

    ISO below 1? Fifteen years ago, I took a Daguerreotype workshop with Jerry Spagnoli at the Photogrpaher's Formulary in Montana. The exposures were something like 30 seconds wide open at f/5.6 in sun or overcast. I started counting backwards and came up with an equivalent "ISO" on the order of 0.005 or something equally useless . . .but it was interesting to do. The sensitized Dag plates were so blue sensitive that UV penetrating the overcast was effective in exposing the plates. . . .so any direct comparison to film was not useful.
    Drew Bedo
    www.quietlightphoto.com
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

  8. #28

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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by Two23
    ......right now on the Northern Plains it's "Sunny 22."


    Kent in SD


    Brad (who grew up in Minnesota)

  9. #29

    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by Drew Bedo View Post
    ISO 25 dry plates? Can you direct me to a source?
    Contact Jason. Or buy from photo dealers, like this one:

    https://www.freestylephoto.biz/18145...25-4x5-10-Pack
    “The secret of getting ahead is getting started.”
    ― Mark Twain

  10. #30

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    Re: Fumbling towards a correct exposure for Dry Plates

    Quote Originally Posted by Daniel Unkefer View Post
    Contact Jason. Or buy from photo dealers, like this one:

    https://www.freestylephoto.biz/18145...25-4x5-10-Pack
    He has an Etsy store and he communicates very cordially and informatively on there...

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