There’s an assumption buried in the protocol for the experiment that led to yesterday’s post: that the read noise of the D810 doesn’t change character over the range of shutter speeds employed in the testing, which were from 1/60 (used to get the histogram that let us estimate the electron counts), and 1/8000 (the highest speed used). Unverified assumptions being A Bad Thing, I thought I’d run a test.
I set the ISO of a D810 to 3200, and made a series of dark-field exposures at shutter speeds from 1/15 through 1/8000, then subjected them to the same processing I earlier used to assess the read noise vs ISO characteristics of the camera.
As a ratio to ideal behavior:
There’s a little spread at the low-frequency, large kernel end of the horizontal averaging, but things look pretty consistent.
Just as a check, there’s the 1/8000 image with a square averaging kernel of 36 pixels:
And the equivalent 1/60 second exposure:
Well, that’s one less thing to worry about.