I'm contemplating a job for a friend shooting artwork, such as watercolors and oils. My plan is to get some polarizing filters for the lights to use with a lens-mounted polarizer.
Then, I got to thinking, (dangerous, I know), about linear polarizers and circular polarizers. Does the type of polarizer on the lights have to be the same type as the lens-mounted polarizers? Or will linear polarizers for the lights work ok with the circular polarizers on the lens?
Thanks.
__________________ Dennis
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
If you will be using a circular polarizer on your lens, why would you need linear polarizers on the lights? I did a similiar project a couple of years ago for my sister and I used the lens circular polarizer and it worked great. Now, I did use natural (sun) filtered light. Once the light is polarized through the lens, does it have any further effect by polarizing it again? Doug K. will probably shed some light (no pun intended) on these questions.
Ron
__________________ "I was really too honest a man to be a politician and live." Socrates.
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
Once the light is polarized through the lens, does it have any further effect by polarizing it again?
Ron
Yes, it does. When shooting any flat subject, especially something like oil paintings, there will be specular highlights from the small irregularities on the artwork, which will tend to blow out detail in the artwork. If you polarize the light emission one way, and use a polarizer on the lens 90 degrees from that, it will eliminate the specular highlights. That guarantees absolutely flat light. (Or so they tell me). I haven't done that particular type of work before, but I'm interested to try it out.
I'm just wondering if the type of polarization is germaine to the issue.
__________________ Dennis
White Balance so easy, even our 5 year old can do it.- Melissa Strickland
Does the type of polarizer on the lights have to be the same type as the lens-mounted polarizers? Or will linear polarizers for the lights work ok with the circular polarizers on the lens?
You may, and must, use a linear polarizer on the lights.
Here's why:
A circular polarizer on the lights would not leave the emitted light linearly polarized, so it would be of no use for your purpose (which depends on "crossed polarization" between the polarizer on the light and that on the lens to attenuate specular reflections from the subject).
(I would be surprised that there would exist circular polarizers of a size for use on studio lights, but of course there might be some use for that I have not contemplated).
With regard to this principle, it will work regardless of the type of polarizer on the lens. The "input" properties of a circular polarizer are identical to those of a linear polarizer, and that is what is depended on for attenuating the specular reflections.
If the camera situation is such that a circular polarizer is needed for use on the lens in "normal" work, then that would be still be true for the lens polarizer in this case.
This would be the case in an SLR where exposure metering is taken from the image after its reflection from the reflex mirror.
The point of using a circular polarizer is that the light leaving the polarizer and passing through the lens is not linearly polarized. (It is variation in the behavior of linearly polarized light obliquely reflected by a mirror, as the direction of polarization changes, that can cause metering inconsistencies in such a camera when a linear polarizer is used on the lens. Circularly-polarized light has no "direction" of polarization.)
Sorry to have to tell all parts of this complicated story!
i use two lights in a cross pattern, V shape on the art, i have shot it many ways. if you are not behind glass lights can be set to read dead even across art even using hard light. something like watercolor wouldnt have any specular surfaces like an oil painting will so hard light alone will do. i shot oil paintings with no glass with hard light and no pols anywhere will my client being very happy, only local contrast no glare spots etc. it can tricky to set the lights exactly right.
a pol on the lens really doesnt do much for art under glass, if not anything other than cut light. i saw the biggest change when i pol'd the lights and not the lens. and then adding the pol to the lens on top of that makes shooting through glass possible.
lucky i had a lin pol from my 4x5 days since i didnt have AF. from what i remember a circ pol is a variant on a lin pol, it still polarizes linearly but manipulates it...not 100% sure.
while i have gone through two brands of pols for the lights, first rosco then visual pursuits, do
put them 1ft from the lights or you will burn them up/discolor them in one shoot and they are not cheap. like $40 for the rosco at like 16x20" each and the VP were $100 each at that size. (from B/H photo). the rosco ones were not recommended to me, but i figure their short life is more a function of how close they are to the light vs the quality.
and from what i understand for cross polarization, you must have hard lights, b/c diffusion spreads the light aka unpolarizing it. but you can use a pol on the lens with soft light.
I shoot a lot of artwork and always use a linear polarizer on the camera as well as polarizing filters on the lights. The one time I tried a circular polarizer on the camera I saw very large color shifts as I adjusted the filter on the camera. That pretty much destroyed my otherwise tightly color calibrated system. I don't see that effect with the linear polarizers. Maybe it was just something about the matchup of light filters to the particular circular polarizer I was using, but it was enough of a hassle to cause me to just avoid them ever since.
Linear Mode
