Cross Polarization with Macro Flash

[bjanes]

I am using the R1C1 flash for taking pictures of pathology specimens and some of the images are marred by glare in the highlights. I have been thinking about using cross polarization by using linear polarizing filters on the filter holder of the flashes and then a circular polarizer on the macro lens at right angles to the axis of the flash filters. Has anyone tried this or have any suggestions?

[michaelnotar]

I am using the R1C1 flash for taking pictures of pathology specimens and some of the images are marred by glare in the highlights. I have been thinking about using cross polarization by using linear polarizing filters on the filter holder of the flashes and then a circular polarizer on the macro lens at right angles to the axis of the flash filters. Has anyone tried this or have any suggestions?

while not a nikon macro shooter, i use x-pol for art all the time. if has to be set up near perfectly. while a circ pol is a lin pol or is closely related, i only use lin pols on the light and lens, and its just because i dont use AF, i shoot med format digital on a view camera with no auto focus.

[Jonathan Wienke]

You will want to use a continuous light source if you cross-polarize, not flash, or else rig up some kind of modeling light. Start with no polarizer on your lights, and adjust the polarizer on the lens to minimize glare as much as possible. Then put a polarizer on the lights one by one, and adjust to minimize glare for each light. Trying to do this with flash only by trial and error is a huge PITA.

Use a circular polarizer on your lens, but linear polarizer is better on the lights.

[bjanes]

You will want to use a continuous light source if you cross-polarize, not flash, or else rig up some kind of modeling light. Start with no polarizer on your lights, and adjust the polarizer on the lens to minimize glare as much as possible. Then put a polarizer on the lights one by one, and adjust to minimize glare for each light. Trying to do this with flash only by trial and error is a huge PITA.

Use a circular polarizer on your lens, but linear polarizer is better on the lights.

Thanks Jonathan, but the whole purpose of spending over $700 on my flash unit was to use the flash unit and avoid the use of continuous lighting and the use of a copy stand.

[Jonathan Wienke]

The monkey wrench in the "set it and forget it" paradigm is that polarization changes depending on the angles of the surfaces of the subject, so the best settings for one subject may work poorly or not at all for another. You can adjust polarizer positions without modeling lights, it just becomes a tedious trial-and-error exercise. If you can rig up some flashlights (LED maybe?) or something as modeling lights so you can preview the effect of the cross-polarization, you can still use the flash and cross-polarize in a reasonably timely manner.

[EricWHiss]

I use this technique often and I've found that some polarizing filters are not up to the job.  Actually I only have one screw in pol filter that will achieve complete reduction of glare - its a B&W MRC Kaseman  - the others I had, Hoya, tiffen, etc didn't work. It's my belief that a linear polarizing filter is going to be the most effective in this situation so is something you might consider - though it may throw off your Auto Focus.   For the lights, I bought some linear polarizing film in a roll for the lights that was very good.  

As posted above you have to be quite careful with your technique.  There is only one orientation of the film and filter that will cancel the glare. Once I found the perfect orientation, I made a mark on my filter for the next time.