Today I repeated the whole series of noise-vs ISO setting tests for the Leica M9.
First, a check for self-heating with a series of repeated 1/4 second exposures of blackness at maximum ISO. Here’s the average value of the noise floor over the series:
And here’s the standard deviation (the noise of the noise) over the series:
Essentially no self heating. The Leica can’t make continuous exposures very fast, which might explain some of that.
Then a test of the noise floor versus the ISO setting at 1/30 of a second, which is the exposure time I’ll use for all the following tests. Sixteen exposures for each data point. Ninety percent of the image area in the sample. First, the average value of the noise floor:
Second, the standard deviation of the noise floor:
Next, the noise in at 200×200 pixel centered patch at 1/30 of a second, with the lens opening and the target brightness set to give Zone VI counts — about 4000. The lighter lines are plus and minus two standard deviations. These graphs include noise floor corrections as described previously:
The above graph with half a stop per stop subtracted out:
It is clear that camera ISO settings of up to 640 help a little over just cranking up the Exposure dial in Lightroom, and that ISO settings above 640 actually do harm.
Let’s look at Zone III — about a count of 500: