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Thread: Light Meter for collodion

  1. #1

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    Light Meter for collodion

    I know that traditional wisdom says that you cant use light meters to measure exposure times for collodion since the process is responsive primarily to the blue end of the spectrum, but I have also heard that people still use them without any trouble at all.

    I was curious if anyone here uses them (specifically with flash) and if so what your results and process are. Do you use the reading straight off the meter? Do you compensate by x number of stops due to the limited spectral sensitivity of collodion?Do you tend to get accurate exposures with your chosen method?

    I am curious because I have a sekonic L358 that meters down to ISO 3, to which I can easily calculate a stop or two of light to get near the collodion speed, and I would love to be able to use it, especially whet setting up lights when shooting indoors, but I have not been able to find any information on the spectral sensitivity that the meter actual reads and uses to calculate exposure, or how that would effect its effectiveness/accuracy with collodion.

  2. #2

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    Re: Light Meter for collodion

    0.5 to 1 is not far away.

  3. #3

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    Re: Light Meter for collodion

    I imagine you could do some tests with your light meter while metering through a blue filter (to match the spectral response of your medium). A #47 blue will approximate that somewhat. You would then have to determine you own personal EI for your material and meter. I imagine you'd have to do some calculating to transfer a reading on the meter at an EI it would measure to the speed of the collodion, e.g., meter at EI 4 and then open up the appropriate number of stops.

    Once done, you should be able to use the meter as a reliable tool, I would think.

    Best,

    Doremus

  4. #4

    Re: Light Meter for collodion

    I use a flash meter regularly with another color-blind process and find it works well as a starting point with one big caveat: Don't assume your process's ISO is what other people tell you it will be, nor that it will be consistent. Different salts and different ages of collodion produce slight different speeds (most likely due to different color sensitivities). I use EV rather than direct measure off my meter and after each plate update a spreadsheet of starting apertures at each EV along with notes about each plate.

  5. #5

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    Re: Light Meter for collodion

    Thanks for the replies.

    I never actually thought about metering through a filter. I might have to try that. It would hopefully at least give me an approximate idea of how much red light is being taken into account by the meter so I can adjust accordingly.

    As for using EV, that is my plan for shooting outdoors, as my meter gives EV values as well, and converting the aperture and shutter speeds from an EV chart would be easy, but again, I wasn't sure how much the readings would be off, given the blue light sensitivity of collodion. Also, It cant convert aperture/speed settings to EV when used as a flash meter, so EV wouldn't be as helpful in the studio.

    Also, I know it is just a starting point, and that numerous factors affect the true speed of collodion, I just wanted to know if I would be wasting a bunch of time/plates trying to use a meter, or if it would actually be useful in the long run. I also plan on keeping detailed info about each plate I shoot.

  6. #6

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    Re: Light Meter for collodion

    I found meters to be pretty much useless for WPC work. I suggest you start by making "test strip" plates and learn how to estimate exposures. You might be surprised how quickly you can learn to judge exposure for wet plate just from experience.

  7. #7

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    Re: Light Meter for collodion

    I know I can make a test strip, and I know how to do it. I also know from my experience with film that I am pretty good at estimating EV, which I can quickly turn into camera settings, but the problem is that these are all useful mainly for shooting outdoors. Estimating exposure/EV is useless in the studio, since the light falling on the scene is the variable you need to figure out, and while you could technically do a test strip with studio flash it seems both difficult and impractical. In either case, having a meter would be beneficial if the readings can be trusted/adjusted: in the field for verifying my estimate, and in studio so I don't waste numerous plates bracketing exposures until I get the right one.

  8. #8
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    Re: Light Meter for collodion

    The one thing about flash that could make it easy is you control the amount, and that should make it consistent. I haven't yet tried shooting the Lane plates using flash, but I do shoot flash at night quite often where flash is the only light (i.e. no ambient present.) In those conditions I know that if I keep distance, aperture, and flash power the same the exposure will always be the same.


    Kent in SD
    In contento ed allegria
    Notte ed di vogliam passar!

  9. #9

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    Re: Light Meter for collodion


  10. #10

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    Re: Light Meter for collodion

    I use an L358 for wet plate with strobes all the time. I've never really bothered with it outdoors, for that I just figure sunny 16 at about ISO 1, make a plate and see where I need to adjust from there. That'll usually get you close enough that you burn at most one plate on sub-par exposure.

    In the studio, I just set the meter to the lowest it'll go, and I basically just don't think about the actual aperture of the lens and instead focus on remembering the number I need to make show up on the display to get a proper exposure. Usually with reasonably fresh collodion and an f/4 lens I'll just start at a meter reading of f/8 +0.5 or so and go from there. With old dead bride at its peak, I'll typically find that around f/11 to f/11 +0.3 is good for a headshot, and a little over f/8 for a wider shot, but the important thing is just finding the magic number for your particular lens/chemistry combo and then using that to work out your ratios.

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