This may be a stupid question, but is it safe to assume that using a circular polarizer slows down AF functions on most lenses / bodies? I have the B&W Kasemann (sp?) and wanted to see how the photos look, especially BIF, when using it. Since they aren't marketed as "loses one stop" or anything similar, I wondered if it would slow down the lens?
Since you already have the filter, simply put it on while watching your camera's metering and you will see how many f-stops you are losing. Polarizers usually decrease light by up to two f-stops.
Any time you cut down on the amount of light passing through your lens, you slow down your AF speed. That is why an f2.8 lens will focus faster than an f5.6 lens.
Jeez. I have to agree with Tony on that, loss of light does slow down Af. I never looked at polarizers losing light as doing that. Thanks Tony for pointing that out.
Thanks gang...
It seems like the equivalent of putting on sunglasses, so the loss of light makes sense. The difference in stops the meter sees is probably dependent on the brightness of the light before the polarizer was applied. I'll give it a shot. I just thought that I had some shots that may have looked better with it on, especially when the "middle of the day" was the only chance I had to get out.
