View Full Version : Determine exposure using polarizer
I could not determine the amount of exposure correction on a sunny day with a po larizer. Looking back, I guess I should have used my incident meter with a shor t piece of toilet paper core, gotten a reading with the tube open, and then a re ading with the polarizer covering the end of the tube, rotating the polarizer, a nd noting the difference in illumination (e.g., 1 stop difference, 1 and a half stop difference, etc.). Any suggestions?
With mine I read the light & open 2 stops. With tungsten lighting in the studio , I open up 1 1/2 stops. Do a controlled experiment on it to find your factors as they do differ with polarizers from different companies.
I did a test with my hand meter in reflective mode by reading a scene without th e polorizer on front, and again with the polorizer in front, and got a differenc e of 1 1/3 stops. In my chromes, they still looked too dark. I went to 1 1/2 sto ps, and they still looked too dark. I have finally come to a 2 stop difference, and this is what I am using now. I recommend you try a few variations yourself. You can probably work this out using 35mm, shooting the same scene with variatio ns on the same roll. Use transparency film. Now, this just compensates for the n eutral density portion of the polorizer. You DO NOT want to correct for the polo rization (usually). Why? Lets take a common example, to darken the sky in a land scape shot. If you have used a polorizer, you know that as you rotate one elemen t, you can vary the amount of polorization, and the sky begins to darken, but yo u notice that not everything in the field of view is affected. The white clouds, for instance, pop out beautifully against this dark sky. They were not affected by the polorizer. So, if you compensated for the polorization, you would simply bring the sky back up to where is was (whats the purpose of the polorizer?), an d you would also blow out all of your highlights as well! You just want to compensate for the neutral density factor of the polorizer, no t the effects of polorization, because a polorizer adjusts the relative contrast of some objects relative to other objects. Now, you can ALWAYS find exceptions to this, and you can come up with an exampl e where the effects of the polorizer will affect exposure (such as glare from a window, now eleminated with the polorizer), but for most nature and landscape sh ots, you probably do not want to compensate for polorization. Practice a bit and gain some experience with it. The polorizer is the most impo rtant filter for color work, IMHO.
Jerry C. Hubbard
Use a spotmeter and read the exposure holding the filter in front of the meter i n the position that you want to use when you take your picture. I use this metho d with all of my filters and it works every time. Don't shoot your finger.
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