I'll be taking photos of old B&W/Sepia portrait photos that are in frames, behind glass. I'll be able to take each one off the wall and shoot it on a stand, with controlled lighting, but I can't take them out of the frames. I had a look at the portraits today, and the glass is very reflective. The frames are about 18" x 24" and the photos within are mostly about 8"x10" in matte, with a few smaller. I can provide nice, even and soft lighting, with one or more sources. The purpose for taking these photos is to produce copies that can be framed and hung elsewhere.
Anyway, I figure I should be able to control reflections to some extent with a CPL filter, and I further figure this will be most effective for one primary light source, which will of course reflect off the glass.
I'd appreciate any hints and suggestions on how to get the best IQ in these circumstances.
I've read @ putting a polarizing filter over your light source in concert with one over your lens will do the trick. I researched it a couple years ago for cost / source, but never had the occassion to need it. I think I found a couple sources via Ebay for for filter media @ light that wasn't too cost prohibitive ... iirc.
Basically, I'm just parroting "Light: Science & Magic" on this one.
This is a standard lighting scenario.. "copy lighting."
Camera focal plane is set to be parallel with the image you are copying.
Set up 1-2 flashes each at 45 degree angles to the picture.
Glass has direct reflection.. the artwork behind it should have diffuse reflection. You will get a nice exposure of the artwork with no reflection.
I've done this several times and it's worked perfectly, even with glossy paper. The gloss seems to reflect directly while the underlying layer with the ink seems to reflect diffusely so it works.. A good book for this is "Light: Science and Magic" (Think I got the name correctly.)
If you want to try and accentuate any texture in the artwork (obviously not relevant for a photo) you can shallow out the angle on the lights and they will provide contrast on the texture. (Probably need to adjust the ratio of the 2 lights as well)
I haven't used the dual polarizer trick.. I want to say that is for a different scenario where your actual subject is more complex and you can't "play the angles" with the light sources. But that one is covered in the book too.
I operated process (copy) cameras for several years in the mid 70's at National Geographic which had glass copy boards and banks of pulsed-xenon lighting. If you place lights on both sides at 45° to the glass with the camera centered on the art and square you will not see the reflections of the lights on the glass. What you may see is the reflection of the camera and everything behind it so you need to hang black draping and poke the camera lens through it.
A simple way to shoot a number of paintings is to make an X pattern with tape on the wall with the center of the X level with the lens axis. To align the camera tape a small mirror in the center of the X. When you can see the reflection of your eye in the viewfinder in the mirror you'll know the camera lens axis is dead center with the center of the X. You'll also want the camera level. You can find bubble levels that mount in the hot shoe at B&H.
Next set up the lights and aim them at the wall at 45°. If you aim both at the center you'll get a hot spot in the center where they overlap. So what you need to do is aim them about 1/3 of the way in from the outer edge of the largest piece you will copy. When you can get it to clip everywhere at the same time on a sheet of white paper as large as your biggest frame you'll know the lighting is even. The further away you can place the lights at 45° the easier it will be to get the lighting even.
From the point where the entire paper is clipping close the aperture 1/3 stop and the white highlights in the art should also be perfectly exposed, about 250,250,250. The amount of shadow detail you'll get with that flat lighting is entirely dependent on the DR of your camera. For most subjects you should be able to record the full range but for really dark subjects you may want to bracket and use HDR to blend highlight- and shadow-detail exposures.
Once you get everything set up like that its simply a matter of putting each piece along the diagonal tape lines (which you'll want to mark with a ruler so the center of the art winds up at the center of the X.
Where you need to use cross-polarization is for paintings with relief such as oils and acrylics where you don't want the specular clues revealing the texture. The problem is light bouncing off at many angles from the irregular surface. To kill the reflections you'll need to put polarizing gel over the flash (both in the same orientation) and then also use a polarizing filter on the lens.
jcolwell wrote:
Thanks for the excellent advice, guys.
I'll try using a shift lens to avoid reflections of the camera itself, plus a dark backdrop behind the camera.
There should be absolutely no need to use a shift lens. Just use the standard 45º repro lighting and you should be fine.
Apart from anything else, by shifting you will be using the edge of the image circle and will not get the best resolution there. A good macro lens works better, and given the small size of the pieces, probably a 100 mm macro lens would be great.
I've done a test setup and I will use a Mamiya C 80/4N Macro on 1DsIII. You're right that shift isn't required, but if it was, my Canon and Mamiya-Mirex T-S lenses would be up to the task, with no significant image degradation for shift up to 10mm.
I have to deal with reflections on a regular basis. The system I came up with roughly translated to your scenario would be to set two lights at somewhat less then a 45° angle left and right, then use barn doors or make a shield to direct the light so the right light is illuminating the left side of the picture and the left light is illuminating the right side. If the frame has some thickness and is also reflective, you'll get a bright streak on the plane of the frame directly facing the light, but it usually looks petty natural.
You can do this with bounced or diffused light, but then the shields have to be large and free standing in the path of the light.
