4 replies to this topic

[Michael Covington]

I should have done this years ago.  I figured out the levels that correspond to positions on the histogram displayed on my Canon 60Da.

All the numbers here are rounded to make it easier for me to do arithmetic in my head in the field. 

Note that the vertical lines are 1 stop apart, and none of them is in the center.

 

[BQ Octantis]

Sweet!

 

That's a lotta headroom even if the top of the histogram hump is at the 4th mark!

 

BQ

[Michael Covington]

For some reason the ADU maxes out at 12000 (not 16384 as I'd expect), and that is 10000 above bias, so only one stop past the last line.

[BQ Octantis]

For some reason the ADU maxes out at 12000 (not 16384 as I'd expect), and that is 10000 above bias, so only one stop past the last line.

Wait, you mean it clips at 12000? Or the top of the histogram is 12000?

[Michael Covington]

When I take a very overexposed frame at ISO 640, the highest DN (ADU) is just over 12000.

That may have something to do with the lesser dynamic range of the higher ISO setting.  I should try a lower ISO.

12000 over bias = 10000 = the equivalent of 13.3 bits rather than 14 bits of output dynamic range.  Not a serious loss.

[ADDED:]  On dark frames the maximum is always just under 16384 (saturated hot pixel).

In normally exposed flats, at ISO 200 and 400 the maximum is 15304; at ISO 640, it is 12650.

Edited by Michael Covington, 18 March 2023 - 06:21 PM.