5d Mark III low iso poor performance.

Started Jun 20, 2012 | Discussions thread
John Sheehy Forum Pro • Posts: 21,221
Re: Take it back

MayaTlab0 wrote:

Does this correspond to what one can see on this graph (The D800 curve is straightforward, while the 5D MKIII curve goes up and down) ?

Yes. The zig-zagging is caused by the fact that the 1/3-stop ISOs on the Canon are pushes and pulls from ISOs that have most of their read noise coming from a later stage, after amplification.

Is it possible on Canon cameras to force auto ISO to use only the optimal stops ?

Not on any that I own.

For auto-ISO, whole stops wouldn't work well with M mode, as the JPEGs and review images would have varying brightness. It is also true that 1/3-stop ISOs will not cause any extra noise in auto-ISO M because, for example, ISOs 160, 200, and 250 all have the same amount of noise with a fixed manual exposure. The 250 will have 1/4 stop less RAW highlights, though, because of the push.

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