Noise level

Hermeto wrote in post #2397471
No, it is quite the opposite!

ISO 1600 with CPL means ISO 6400.
Or, as per your exapmle, 400 with CPL equals ISO 1600.

Polarizing filter doesn't not affect the ISO (which is the amplification of light). It reduces how much light hits the sensor for a normal exposure, but it will not make your shot less or more noisey.

Polarizing filters affect the exposure not the image quality/noise.

eaglesnest wrote in post #2397460
If I set my ISO at 1600 and put a Polorazing filter, it means 2 F stops less. Thus I actually shoot with ISO 400. The noise level I get is it equivalent to 1600 or 400? Thanks for the info.

Hellashot, I agree with you (and the others) that CP doesn’t affect ISO, but if you read the OP carefully, you’ll see that question refers to noise introduced by higher ISO.

I should have been more precise with my answer: if exposure is affected by using CP in ISO 400 (assuming that shutter speed and aperture are NOT changed), noise in the picture AFTER the exposure adjustment in post processing will be the same (if not worse) as if ISO 1600 was used.

I guess it’s just my broken English..

superdiver wrote in post #2399341
This has been my experience...not sure if its "scientific" or not, but when you UNDERexpose due to filters and then adjust in PPing the noise levels INcrease dramatically. I can understand how tthere can not be a TRUE ISO comparison, but the effect is ALOT more noise...

Yes, UNDERexposure results in more noise when you postprocess to increase the 'software gain' analogous to the hardware gain (amplification) that higher ISO brings. Same fundamental issue, that a low signal (low light) and the inherent noise ALL GET amplified in software or hardware!