Using colored filters to photograph gravestones
March 1, 2010 9:22 PM   Subscribe

I want to get some feedback on my idea for photographing eroded gravestones before I go out and buy the materials to test it. I propose taking two camera flashes and putting green film over one and red film over the other. Then I'll mount one on the left and one on the right of the camera. I hope that this will give green shadows on one side of the carvings and red shadows on the other, and by fiddling with the resulting photo in Photoshop I'll be able to see the faded carvings better. Does this sound as though it would work? Could I get by with a single coloured flash? Is there a better way?
posted by Joe in Australia to Technology (13 answers total)
I don't really get what 2 different colored flashes is supposed to do. I think the main result will be that flashing from both sides at once will do the opposite of what you want: it will fill in every bit of shadow, resulting in lack of contrast and detail. Basically, there will be NO shadows, because each flash will be filling in the shadow from the other flash.

Your best best is to light the surface with a single flash at an oblique angle. This will create contrast, leaving the carved parts in shadow. (This assumes the stones are not in direct sunlight, which would negate any light from the flash.)

And, since you're using Photoshop, the levels, curves, and contrast tools will do wonders in bringing out the details.
posted by The Deej at 10:15 PM on March 1, 2010

Deej: As I understand it, the intent is to take two simultaneous obliquely-lit photos lit from different angles, using the red and blue channels of the camera to record them.

I think that you'll have trouble completely separating the two channels again, though, since most of the hardware and software isn't designed with that in mind. What about putting the camera on a tripod (or other stable mount) and taking two successive photos, with the flash in a different place?
posted by hattifattener at 10:20 PM on March 1, 2010

Also I have a vague memory of seeing an article about using this technique for archaeological-type research. I found this article but I don't think that's the one I remember.
posted by hattifattener at 10:28 PM on March 1, 2010

Response by poster: Hattifattener: Yes, that's my plan - I'm hoping that by highlighting everything that is abnormally red or abnormally green (or abnormally un-red or ungreen) I will have identified the edges of the carvings. But I don't know if this would work.

The problem with using a tripod is that it takes time to set up. I'd like to be able to move down a row of tombstones, firing off a shot at each one. This way I basically have a camera with a pair of flashes off-center, which is bulky but not impossible.
posted by Joe in Australia at 10:58 PM on March 1, 2010

I wonder if you'd have better luck doing it in two separate photos and then merging them on the computer: one with one color on the left, the second on the right with the other color.
posted by piedmont at 11:15 PM on March 1, 2010

If you have both flashes mounted on your camera, they'll only be a few degrees apart relative to the target, which won't be enough to cause noticeable colored shadows. I think they'd need to be separated by a meter or even two in order to get a satisfactory result.
posted by Chocolate Pickle at 12:09 AM on March 2, 2010

I've photographed faint rock carvings and it helps a lot to get them wet before you take the photograph too.
posted by fshgrl at 12:13 AM on March 2, 2010

I have had success bouncing flash (or just available light) from a big white reflector, off to the side. It doesn't have to be pro equipment -- I use a big piece of insulating foam with a stick to prop it up. Even a tripod draped with a white towel will work if you find yourself unprepared. Try to go at a time of day when the sun is neither directly behind or in front of you. Cloudy days are good.

This article may prove helpful. If you're doing this for genealogical purposes, the names and dates will be what you're after, but if you're looking for epitaphs, even recording a few of the words will be enough for you to Google up the rest.

Whatever you do, don't put any substances on the stones. A little bit of distilled water won't hurt, but if anyone suggests you spray anything out of a can, please be advised that they, like the people who advise you kill and then stuff your victim for wildlife photography, are not on the side of conservation.
posted by Sallyfur at 2:04 AM on March 2, 2010

Mounting the flashes to the camera won't really reveal the surface texture of the eroded stones. To best reveal the texture use a flash off to the side of the stone. A single flash will probably work better than dual flashes in this circumstance. Buy one and try that. It may require experimentation depending on the type of weathering.
posted by JJ86 at 5:55 AM on March 2, 2010

The red & green flash thing is interesting, but unless you're doing some kind of machine vision work, I think it's not the way to go. Assuming that you or another human will be looking at the images and reading off the inscriptions, just go out on a cloudy day and set up a single, ungelled flash at an acute angle to the surface of the stone. Make sure it's on its own stand, not mounted to the camera. You probably don't need to bounce it off a big white reflector, but if you find the shadows distractingly harsh when shooting the flash in directly, give the reflector a try.
posted by echo target at 6:40 AM on March 2, 2010

I'd tend to go with a long flash cord so you could shoot with raking light, the angled flash as described above. It's fairly mobile, but if you had to do it all day, your arms would get a bit tired.
posted by advicepig at 6:51 AM on March 2, 2010

Do you want to read the carvings, or get interesting photographs?

If you want still photos, perhaps the methods of obtaining HDR (high dynamic range) photos by taking multiple exposures and then merging later would work?

If you just want to archive/ read the carvings, why not try video rather than still photographs? This way you can physically take multiple angles and can find the most appropriate after the fact.
posted by NoDef at 7:06 AM on March 2, 2010

I know this isn't quite in keeping with your original idea, but have you checked out Strobist?

I realize the facings are a bit more 3d than the 2d used here, but I think there's stuff you can use here.
posted by rooster416 at 7:32 AM on March 2, 2010

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