I’d like to set the gain of this camera to 150. If I select camera “ZWO” I can do this, but I see it is not supported.
If I use camera ASI(1) gain can only be set from 0-100. If I take an image like this, the FITS header reports Camera Gain 100, and eGain .242… Those match.
But how to I set the camera to higher gains?
I want to be sure I’ve hit the knee of the best compromise between read noise and DR.
The ZWO ASCOM driver limits the gain to 100, so there’s no way to go above 100 with “ASI(1)” (ASCOM).
Is there a particular reason you want to go above 100? Anything above 100 only adds read noise without much other benefit.
Why would they limit gain to 100 when in their own tutorial on the ASCOM driver, they demonstrate gains from 0 to 300 (lowest read noise)?
Higher gains result in lower read noise.
Where are you getting your information, it seems opposite to what I am reading.
The camera manual shows a read noise of 1.4e-rms at a gain of 150. at a gain of 0 the read noise is 3.4. I want to set it at 150.
If you look at the camera characteristic plots on the ZWO product page for the ASI2600, you will see that there is a dramatic drop in read noise at gain 100. It goes from above 3e- to 1.4e- as you state.
Technically you are correct that after gain 100 there is still a light drop in read noise with higher gain, however that drop in read noise is very, very small after gain 100. And after gain 100 you start losing full well capacity quite quickly. For deep sky imaging there is no real advantage to going beyond gain 100 for the very slight improvement of read noise while sacrificing lots of full well capacity.
Now for things like planetary imaging where you want to use lots and lots of really short exposures, higher gains would be good. But in that case you probably wouldn’t be using SGP because it’s not meant for that kind of imaging.
Well, it turns out, ZWO limited the gain setting to 100 in the ASCOM driver, because ‘people who use ASCOM image DSOs’ and so ‘people wouldn’t make a mistake’. Found this on their bulletin board.
That’s a bit of nonsense I think. The break point (unity gain) for an ASI294 camera is about 125. Can’t set this value! It varies depending upon the camera. I’m not sure 100 hits that break point for the 2600. Too hard to read the graph at that granularity. Anyway, setting the gain anywhere between 0-100 only effects the DR. What is the point of that? They may as well have fixed the gain at 0, just like they fixed the offset.
Anyway, there is a reason to set gain past 100, even though DR is then only about 10K. If the object is very faint, one can take shorter exposures because of the lowered read noise. See SharpCap author for setting the optimum sub exposure times for a given camera.
Looks like I’ll have to take this up with ZWO. Any reason SGP doesn’t support the native driver anymore?
Just one comment for ASI2600: From gain 100 to 150 the FW is reduced from around 18K to 10K !!!
Also, tne read noise on those two gain settings is about the same.
I think is is important to consider FW over a very flat read noise curve.
The breakpoint may be 102, not 100. You cannot tell from the graph.
In some circumstances, 10K FW is OK.