Noise... camera ISO sweet spots?

Started Dec 28, 2012 | Discussions thread
John Sheehy Forum Pro • Posts: 19,137
Re: Noise... camera ISO sweet spots?

Ubilam wrote:

I see something that seems to be ignored here. The same camera can have more noise just a step or two up and then its clean again...ie: iso 100 can be as clean 320. 125 as bad as 400. Some high ISOs near to each other vary too more or less. Whats up with that?

What are you looking at? Many camera JPEGs and/or external converters apply more noise reduction at higher ISOs, and/or in the shadows, so what you see isn't really what the camera is recording. Also, some cameras, like most non-1-series Canon DSLRs, use digital gain for 1/3-stop ISOs like 125, 160, 250, etc, and can have their post-gain, late stage noises boosted for a lower ISO than another ISO at which that noise can be attenuated, such that ISO 125 could have 2/3 stop more shadow noise than ISO 160, or even ISO 320. In fact, the dark frame noise on many Canon DSLRs is as high at 125 as it is at ISO 640 or even 1250. Banding noise is more easily visible when other noises are low, especially for images displayed very small. People have reported using ISO 640 on their Canon 5Dmk2 where they would normally have chosen base ISO (100) because even though the late stage noises are the same at both ISOs, the higher photon shot noise of 640 masks the banding that is visible at ISO 100.

Then, you have the issue of thresholds. Noise may be such a small part of the IQ at high exposures that doubling or halving it is imperceptible.

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