Noise level

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.

No, it is quite the opposite!

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

How can it be? By putting a Polarizing filter, the sensor will get less light,
means your ISO also drops by 2 f stops. Am I right?

wait, what????

iso is iso, it isn't affected by anything but the level you put your camera in (50, 100, 200, 400, 800, 1600, 3200)

your METERING on the other hand will need to compensate for the lower amount of light. for those 2 stops, you will either need two stops faster av (what needed 5.6 will now need 2.8 for same shutter speed and iso), or two stops slower tv (what would need 1/1000th will now need 1/250 for the same av and iso settings), or you would need to bump up the iso from 400 to 1600 to keep the same shutter and av values.

basroil wrote in post #2397639
wait, what????

iso is iso, it isn't affected by anything but the level you put your camera in (50, 100, 200, 400, 800, 1600, 3200)..

I do agree

eaglesnest wrote in post #2397497
How can it be? By putting a Polarizing filter, the sensor will get less light,
means your ISO also drops by 2 f stops. Am I right?

If CPL reduces amount of light on the sensor by 2 stops, that 2 stops of light have to be compensated somehow.

You can do that by using 2 stops larger aperture, 2 stops longer shutter speed, or 2 stops higher ISO.

Put in simple terms. A polarizer is like being in light that is two stops darker.

Exactly!
It kills 2 stops of available light..
How you are going compensate that, depends on the effect that you want to preserve..

Thanks for all your response. But you missed my question. I simply ask for the noise level effect.

That is quite possible.
Can you rephrase your question please?

If you set the camera to ISO 1600, the noise level will be the same whatever you put in front of the lens. So no, the noise wil absolutely NOT be the same as ISO 400! If you compensate for the loss of light by changing aperture or shutter speed then that's all there is to it.

If, however, you keep aperture/shutter speed the same then the image will be under-exposed by 2 stops. In that case, the noise level is still the same (i.e. ISO 1600). BUT - when you process the image to compensate for it being too dark, you will amplify the noise so that it looks more like ISO 6400!

noise is mainly (but not always) determined by your ISO setting, period.

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.

You're stil shooting at ISO 1600, just with less available light. ISO isn't related to the amount of light coming into the camera through the lens; it's a measure of how much the signal from the sensor is amplified. So you'll still get ISO 1600-level noise.

If you put a polarizer on your camera, you get 1/4 as much light (2 stops less), but the ISO doesn't change. The 2 stops light loss just means that you'll be getting the same exposure that you would if you had the camera set to ISO 400 but without the polarizer, not that the ISO is changed. The camera doesn't even know whether you've mounted a filter or not, so how could it alter the ISO setting?

ISO on digital cameras seems to not be understood well. Essentially (perhaps oversimplified) the ISO value goes up when the amplification of the signal hitting the sensor goes up. But it isn't only the real signal, it is also the inherent noise in the circuitry that gets amplified. I have prepped a chart showing this effect, where high ISO lowers the signal:noise ratio so that we see the noise.

gcogger wrote in post #2398664
If you set the camera to ISO 1600, the noise level will be the same whatever you put in front of the lens. So no, the noise wil absolutely NOT be the same as ISO 400! If you compensate for the loss of light by changing aperture or shutter speed then that's all there is to it.

If, however, you keep aperture/shutter speed the same then the image will be under-exposed by 2 stops. In that case, the noise level is still the same (i.e. ISO 1600). BUT - when you process the image to compensate for it being too dark, you will amplify the noise so that it looks more like ISO 6400!

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...