Polarizing filter question.

A couple of questions regarding polarizing filters:

#1. Is it common practice to increase exposure when using a polarizing filter? I'm looking to achieve a deep blue sky color which leads me to the second question...

#2. What is the best position of the sun and time of day to maximize the effect of the filter for the sky.

I'm curious to hear what you have to say. You can read books but it seems to me that by trying it yourself and asking experienced people is the best way to learn.

Thanks,
Alan

You definately have to increase your exposure by 1 or 2 stops, sometimes more. The amount of polarized light varies, so you have to experiment. A polarizer cuts out a lot of light, so you need to compensate even if you want your skies dark blue.

As a "rule of thumb" (pun intended), extend your pointing finger and your thumb. Point your finger at the sun. Rotate your wrist and your thumb will point at the areas of maximum "blueness" in the sky. Obviously, you need to have some blue sky showing; cloudy days aren't good for polarizers (except for things like eliminating reflections from glass, etc.).

Your TTL metering should compensate for the loss of light.

The short version of the rule of thumb is: angle your lens at 90 degrees from the sun.

These were shot Saturday with a 20D, 16-35 f/2.8 and a B&W 77mm Circular Polarizer. I used partial metering off the sky. You try to position your lens at 90 degrees to the sun for maximum effect and rotate the outer ring of the CPL to get the effect you want.

Thanks.

Has anyone found that due to the darkened sky, the camera (20D in my case) tends to overexpose by about half a stop (depends on the amount of sky in the image)?

I usually have to compensate or meter entirely of the foreground to get nice skies like Scotts first shot there.

This was taken on my G2 with a linear polarizer. As long as you're patient, you just spin the polarizer until you get the look you want.

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In general, no. If anything, my camera underexposes blue sky with a polarizer.

When it gets a little weird is if you are using a fairly wide lens. The degree of polarization changes radically when you go from one side to another on the wide lens, whereas, it would not be so different with a longer lens. Anyway, the result is that you can get a very light sky on one side and a very dark blue sky on the other side. So some viewers claim that it looks fake. You can avoid some of that complaint by not cranking the polarizer all the way to its maximum. I've tried about 50% with good results.

---Bob Gross---

what reasonably priced polarizing filter would you recommend for the Canon 20d? (I know pretty much nothing about quality issues on this topic)

B&W or another high quality multicoated Circular Polarizer.
It doesn't pay to put a cheap filter in front of a good lens.
Scott

are the canon polarizers any good? nobody ever seems to mention them

Which lens? Scott is right ...............DON'T use a cheap filter.