ISO and SNR - I'm confused

N

ninjaleprechaun

Active member
Perhaps one of you kind people could help me with this.

How do you impliment an ISO rating on a video shoot? And what is its practical purpose? Is it that having more light will produce a picture with less noise than a picture of equal output brightness that was shot with less light but with the iris open more? If this is not what the ISO rating is for, then what do you call it?

I hope my question is clear. Thanks in advance for any help.
 
Most people rate the DVX at 320 ASA/ISO, some people take it up to 500. The ISO is how you determine the correct exposure level for the camera. Adding filters such as a Polo or color filter, or even diffusion such as a Black Promist of 1 or more will affect the ISO, bringing it down. Changing the "shutter speed" will change the ISO.

check out:

http://en.wikipedia.org/wiki/Film_speed
 
By "correct exposure level", do you mean what F-stop is optimal? The reason I ask is that I seem to get less noise in the picture if I expose at F2.8 (for example) with the ND filter on and more light on the set than at F2.8 with ND off.
 
Hmm.

Are you saying that the ND filter reduces noise? That seems counterintuitive.
 
No, I guess I'm saying that having more light seems to reduce noise in two pictures of equal output brightness. It's not the ND filter reducing the noise, but the fact that there is enough light to warrant the ND filter to still expose at 2.8 or whatever exposure you'd like. This is all just based on observations I've made through personal experience. i thought this might be what ISO ratings are in reference to, but I guess I was wrong, so I don't know what to call it.
 
The ND filter changes the effective ISO of the camera. If you rate it at 320 then put an ND on, then you would have to rate the camera at a slower ISO.

Having enough light for the chip to make an image reduces noise. This can be done with lights on the set, *NOT* using an ND filter, or by shooting at a slower shutter speed.

Shooting a scene at f2 with a 1/8ND filter produces the same ammount of light as shooting a scene at f5.6 with no filter. There should be change in the noise level, but you will need 8 times the light if you shoot with the ND filter on!
 
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