I’ve been using cross-polarization in some of my studio work lately, and some have asked me about the benefits of this approach. In order to demonstrate them, I’ve created my first animated GIF.
This is an a7III shot, using the CV 65/2 Apo-Lanthar and cross-polarized light. I set up a Godox 600 TL Pro strobe with a 16-inch beauty dish attached, and the grid that came with the dish in place. Before I snapped the grid on, I taped a piece of Rosco neutral polarizing gel to the inside. Then I put a 67-77 mm step up ring on the lens, and a linear (although this technique works with a circular one) polarizer on the ring. I set the strobe for a full 600 watt-second pop. I opened up the lens to f/8, and set the polarizer on the lens to the point where the specular highlights were almost, but not quite, gone. 600 ws not being quite enough, I cranked up the ISO a bit, which was probably unnecessary. I didn’t go all the way to 640 because I didn’t want blown highlights, but it turns out that I could have gone that far easily.
Then I turned the polarizer on the camera so that it was aligned with the polarized light, and turned down the power setting on the strobe to compensate. I processed both images identically in Lightroom.
For my subject, I chose a pomegranate branch with some buds. Those of you who know the trees will remember that both the leaves and the buds are shiny as all get out.
I think you can see the benefits of the cross-polarization. The shiny leaves and buds are not sullied by the specular highlights that appear in the image with the polarization aligned.
One of the downsides of cross-polarization is that it wastes a lot of light. If I had used ISO 100, I’d have needed a 2400 watt-second strobe or would have had to use four pops.
Back in the day, I would use cross polarization when doing high end fine art copy work.
Using a dozen high power Lowell tungsten lights, a better light scan back on a Toyota 4×5, art ( oil painting originals, sometimes VERY large ) tacked up on a wall.
It would take me several hours to get the lighting perfectly even and flush on the wall ( within a tenth of a stop ). Another hour or two to get the view camera perfectly perpendicular to the wall. I did create a luminescence capture of a bare wall at high bit depth. Inversing this capture, full desaturate, and a levels move with a small amount of noise ( .58* Gaussian monochromatic ) to create a correction mask for “hot spots”.
Depending on the sheen, the amount of polarization would very. The exposure was usually 1/10 of a second per line. A full res capture could take 45 min or more.
The quality of a properly setup betterlight capture is in my opinion still the good standard, when possible.
*Neat fact: in photoshop, fill a layer with 50% gray. Zoom in to 200-400%, check out the difference between .58 mono gauss noise and .59. Quite a big diff.
I too use cross polarization for fine art duplication. Capture One’s Lens Cast Correction tool is great for equalizing the exposure across the frame by simply capturing a frame of the white background and using that frame for LCC. The biggest challenge I’ve found is that cross polarizing creates color challenges making it much more difficult to get exact color matches. I don’t know the science behind it but even with a nearly perfect color and tone match to a Color Checker for reference paint colors can look different under cross polarized light.
I’ve noticed that, too. I don’t understand it, either. Is is possible that diffuse specular reflections are dulling the Color Checker patches when they are sampled under unpolarized light? In that case, calibration would have to take place under polarized light.
It’s also possible that some paint affects the polarization in unpredictable ways, much like some plastic does.
I’ve done cross polarization with a circular polarizer on the camera side.
You don’t need both polarizers to be linear, only the light source side.
I took electromagnetics twenty years ago, so I could be missing something, but I also thought this would work with a CPL on the lens, since a CPL (nominally speaking) filters with a linear polarizer and then re-circularizes the wave with a wave plate.
Yes, it does work with CPL on the lens. Using a CPL may lead to less colour shifts (may depend on sensor, I checked only a few ones). However I also, like Jim, use linear pol. on both light source (if the light source is a flash, Lee glass linear polarizer does a better job for me than Rosco gels) and lens because it seems to be more effective and easier to profile – the colour target needs to be measured with a pol. filter on the spectrometer, and readily available filters are linear. I never got profiles I like for CPLs if using traditional (non-spectral) profiling methods.
Thanks, everyone, for the correction on the circular polarizer. I’ll change the text.
I am using this to shoot paintings. One CPL on the flash YN560IV and one on the lens. It completely removes the reflections from the canvas. I really want to try portraits but it is almost impossible to find bigger sheets of polarized film in Europe at least not at a reasonable price.
Hi, Simeon. Bought these on Amazon.ca, should be available in Europe as well. $20.50 CDN, includes shipping. I cut one sheet for three Canon 580 EX II’s and one sheet for a Godox AD600. Using mainly for cross polarization lighting of insects.
Link to seller: https://www.amazon.ca/Polarization-Polarizer-Educational-Polarized-Non-Adhesive/dp/B0787VMR6D/ref=sr_1_1?ie=UTF8&qid=1533062082&sr=8-1&keywords=90%C2%B0+linear+polarizing+film&dpID=41cgBVGLTfL&preST=_SX342_QL70_&dpSrc=srch
Hi, Simeon. Bought these on Amazon.ca, should be available in Europe as well. $20.50 CDN, includes shipping. I cut one sheet for three Canon 580 EX II’s and one sheet for a Godox AD600. Using mainly for cross polarization lighting of insects.
Link to seller: https://www.amazon.ca/Polarization-Polarizer-Educational-Polarized-Non-Adhesive/dp/B0787VMR6D/ref=sr_1_1?ie=UTF8&qid=1533062082&sr=8-1&keywords=90%C2%B0+linear+polarizing+film&dpID=41cgBVGLTfL&preST=_SX342_QL70_&dpSrc=srch