View Full Version : Light Meter for collodion

15-Oct-2018, 09:34
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.

15-Oct-2018, 10:01
0.5 to 1 is not far away.

Doremus Scudder
15-Oct-2018, 10:51
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.



Jason Greenberg Motamedi
15-Oct-2018, 11:02
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.

15-Oct-2018, 12:46
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.

15-Oct-2018, 14:28
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.

15-Oct-2018, 18:02
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.

15-Oct-2018, 18:31
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

15-Oct-2018, 18:31
This will work.

15-Oct-2018, 19:33
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.

15-Oct-2018, 19:34
Oh, and of course the meter tops out at ISO 3 and f/22, so try to at least get a fast enough lens/collodion combo that you can use less power than that ;)

15-Oct-2018, 19:38
I don't use meters for wet plate. The chemicals all age at different speeds and effect the exposure times just as much as the light. Consistent use and practice will get you in the ball park for a first plate. Make adjustments from there and you are usually good to go.

16-Oct-2018, 05:11
Im familiar with using flash and how it works. Figuring out the needed flash output for proper exposure via bracketing and then keeping everything consistent, or making adjustments in distance via inverse square etc is all well and good if I only want to shoot one light setup. If I want to use more than one set up, multiple lights, etc, having a meter would still be a great time/money saver. I mean if I use a meter in the studio with digital, which is fast and costs nothing to shoot as many test frames as I want, why wouldn't I try to use it with a much slower more expensive process?

As for different collodion being different speeds, and other factors like age affecting speed etc, I am also aware of that issue, but that is the case regardless of whether or not I meter the light with a meter or estimate based on experience, so I guess I don't quite see it as a reason to not use a meter.

@bieber thanks for those starting points. In continuing my search for information on the subject I also found another post buried on a different collodion forum that mentioned very similar starting points for flash.

30-Oct-2018, 07:01
I use a meter with collodion and strobe. Mine goes down to iso 3 but if I get a reading of f/11 I'll have enough light to shoot at around f/5.6 with some wiggle room for under/over developing in the darkroom.