I thought I'd come back and post my results with the polarizing setup for documenting my daughter's paintings. She works mostly in oil but occasionally with a background of acrylic when she wants a flat, featureless background. Her work is extremely finely detailed and she is extremely particular in documenting her work for her own use as well as catalogs and website that there be no artifacts visible.
For oil paintings the two big flaws are often little points of light reflecting in a specular fashion that are never noticed when in the gallery with broad diffuse lighting and glare: large areas of specular reflection. Lastly non-uniform illumination which usually shows as a gradient.
In the past we've used flashes and big umbrellas but it was always a struggle to get something passable. The results took hours of retouch time in Photoshop which could be much better spent doing compositions for new work.
This thread came at a perfect time as it allowed me to rework our lighting. We just finished shooting the last two works of this series which will be on display at her opening this weekend. Down to the wire!
The results were nothing short of excellent!! She will have zero retouch time on the works shot with the polarizer setup. The setup wasn't cheap but it is an easy one year payback so it's a no brainer investment. She's one happy artist!
We used two Profoto D1 1000w/s lights with 6ftx1ft softboxes covered with polarizing film. The D300 camera used a 77mm Nikon circular polarizer (CP).
Spend time with the circular polarizer and the polarizing film to find the point at which light is maximally attenuated and somehow mark that point on the CP. On our polarizer that point turns out to be conveniently the "C" in circular polarizer printed on the unit. When aligned upwards the output of the lights was maximally attenuated.
The cross polarizers attenuate anything specular. The painting surface actually has a slight diffusion property which scrambles the polarization and that passes thru the CP in opposite polarity. The specular light from the same surface is often seen as glare and is very difficult to edit out later. The CP when properly aligned with the polarizing film on the softboxes completely eliminated this from all of our shots. Also no little light nits were visible.
We initially started with 4ftx1ft softboxes and found them insufficient to evenly illuminate her 4ftx6ft works. There were gradients top and bottom as a result. The 6ftx1ft boxes completely eliminated the gradients.
I was very glad I got the 1000w/s lights. It made it possible to move the softboxes back to 10ft and still shoot at ISO200 f/8. Softboxes and polarizers eat a lot of light.
The polarizing film is 17.25" wide and is sold by the foot. I got a 4x8ft sheet of 4mm black coroplast and made a frame 3" wide window frame to fit around the edge of each softbox. To that is attached the polarizing film with binder clips. That allows me to roll up the polarizing film for safe keeping and makes it easy to transport.
I bought and used a simple Sekonic 308 to ensure uniform illumination of four corners and center of artwork. Easy.
Big thanks to Jason DiMichele who provided lots of help in getting this done!
Here's a link to her upcoming show:http://www.connersmith.us.com/exhibitions/katie-miller-enduring-solo-agniet-snoep-alive-and-present-solo/