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Old 05-06-2016, 06:53 PM
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Shiraz (Ray)
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Shiraz is offline
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,820
Originally Posted by Slawomir View Post
Thank you Ray for helping me to get a better understanding of functioning/parameters of the new ASI camera

Actually I have never measured background signal before, so it was interesting to notice that in my 10-minute subs captured with 3nm Ha there is 102 ADU of background signal give/take a few ADUs. Gain is 0.26. That's a lot of unwanted signal!

Also, while I had my camera powered up, I wanted to see how a 300s dark from my current camera compares with the one from ZWO's website, so I just took a 300s one and did a bit of measuring on both using stats tool in PI. By no means I want to judge which one is better, I simply want to know how things are shaping up with the newcomer from ZWO. I can see that AVD, MAD and mean ADU values differ for both cameras, but I am not sure whether these should be somehow scaled to be able to truly compare the data?

Anyway, here are the results I've got:

AVD = Average Absolute Deviation
MAD = Median Absolute Deviation

entire 300s dark at -25C (from ZWO website)
Mean 154.3
AVD 14.9
MAD 23.7
Min 17.0
Max 23937.0

QSI690 (gain 0.26)
entire 300s dark at -25C
Mean 502.9
AVD 13.2
MAD 11.9
Min 419.0
Max 25952.0

a small central area of a 300s dark
Mean 152.7
AVD 14.1
MAD 23.7

QSI690 (gain 0.26)
a small central area (the same size) of a 300s dark
Mean 503.2
AVD 13.2
MAD 11.9
Thanks very much for the info Suavi.

if you wish to do a direct comparison, I think that you need to get all of the data into electrons and account for the different read noise (the 1600 at the gain used for the ZWO dark has >3.5 electrons read noise). Actually, thinking about it, an apples-to-apples direct comparison is likely to be quite difficult/impossible - there are just too many variables with the 1600. eg, setting the gain on the 1600 to give similar characteristics to the 690 may not be optimum for the 1600. Nonetheless, your results at least show that the two cameras are not different by orders of magnitude, so there is nothing drastically wrong with the 1600.

If your NB background is 100ADU at 0.26, you have 26 electrons sky background. That is more than the brightest dark current region in my 1600, so, for reasonable QE in the 1600, sky noise in your system would overwhelm much of the extra noise from the "glow" in a 1600 - should you ever decide to try one - but why would you with your nice camera.

edit: I am surprised that the MAD values do not change with region selection - not sure what that means.

Last edited by Shiraz; 06-06-2016 at 05:39 AM.
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