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mustang85
11-15-2006, 02:03 AM
Hi, just wondering when you thought a polarising lens should be used and also, i've noticed that with the filter on i've had to use a slower shutter speed to let more light in. Is this correct??

THanks

sla
11-15-2006, 03:24 AM
Hi
As far as I know, polarising filter stops some light, makes parts of images darker (the parts from where it removes reflections). Like on these images:
http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/filter/polarizer.html
and on landscape image on this page:
http://www.colorado.edu/physics/2000/polarization/polarizationI.html

In such cases average amount of light in the image overal is smaller, so longer shutter may be expected, I think. But not necessearily. If you won't increase shutter time, you wil simply get partially darker image. In many cases this means more contrast (this is one of reasons why we may want to use it).
Regards
S.

mustang85
11-16-2006, 10:51 PM
thanks. Another thing i just thought about is using a lens hood with a polarizing filter because with the hood on, it is impossible to move the polarizing filter to the desired effect. Are hoods not to be used with these filters?

AlexMonro
11-17-2006, 04:14 AM
I can use the lens hood on my Fuji S9500 with a polarising filter, though it is a bit more fiddly. You can also get lens hoods that screw on the front of the filter, so you rotate the hood to rotate the filter.

For many effects (darkening blue skies etc.) the polariser works best with the Sun to the side, so the hood is less essential anyway.

SpecialK
12-09-2006, 05:51 PM
A polarizer reduces glare (and relections in glass) which gives saturated colors, most effectively seen with a daker blue sky. It does not really affect contrast. It doe reduce the exposure by perhaps 2 stops.

I forget which camera has it, bu the lens hood has a little hatch in it which allows you to rotate a filter.