Gain setting conundrum

[Dave_S]

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Sensor analysis on the Hyprercam 294c Pro camera.

Now having a good quality Light Panel, with a variable output, primarily for 'Flats', this afternoon, I ran a Sensor Analysis using the excellent application in Sharpcap. I did this when I first bought the camera, but with a less suitable light source.

 Today the setup was more refined, and controlled.

 The resulting table showed and e/ADU of 1.68 at a gain setting of 100 (the lowest setting on the Sharpcap gain scale), and an e/ADU of 0.95 at a gain setting of 177.

 By interpolation, this puts unity gain (1.0) at a gain setting of 172.

 However the gain/read noise graph shows a sharp drop in read noise at a gain setting of around 900 (again on the Sharpcap scale). The level of read noise remaining low, and flat from that point on upwards.

 The conundrum is, SharpCap's gain scale goes from 100-72000, whereas AA8's (ASCOM) gain scale goes from 1-50, with other software using different numbers altogether, to represent what is actually the same gain level. All very logical to the end user of course, NOT!!.

If I want to use AA8, which I do, I need to transpose Sharpcap's 100-72000 gain scale in Asrtoart's  1-50 scale. If my thinking is correct, then a gain of 900 for example, in Sharpcap, equates to a gain of 9 in Astroart (ASCOM), or does it?, I have yet to find a definitive answer to this question. Imaging was relatively simple by comparison when we were using CCD cameras.  No gain or black level settings to get right, and no green tinted images . Ok, CMOS is cheaper, and more sensitive, but there is no such thing as a 'free lunch' I guess.

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[fabdev]

Hi, I've found this:

https://aptforum.com/phpbb/viewtopic.php?t=2700

which seems to confirm the 100:1 rule.

Another solution would be to repeat the Sensor Analysis in Sharpcap using the ASCOM connection.

[Dave_S]

Hi Fabio

Thanks for that Fabio.

I will have a look at that Link, and also re-run the sensor analysis using the Ascom driver in Sharpcap, then report back here.

I never thought of that option, "good thinking Batman"

Regards

Dave

[Dave_S]

Ok, I have just run the Sharpcap sensor analysis on the 294c using the ASCOM camera control.

Unfortunately, I am none the wiser, because the resulting table, graph, and gain numbers, are identical to that obtained using the 'native' Altair driver. So even though under ASCOM control, it still returns the same numbers, which are x100. x100 on what base, I don't know.

I will keep searching for a definitive answer.

It was never an issue with CCD, as there was no gain or black level setting to 'play' with. Just select a suitable exposure time, and go.

[fabdev]

It's possible that internally the Altair ASCOM driver still uses the 100X range, and the smaller range is only used in the Dialog Window of that ASCOM driver, maybe as a mnemonic aid to the user (?) A test in SharpCap could be to set a Gain in the ASCOM Dialog Window, and then reading the FITS keyword about Gain of an exposure.

[Dave_S]

I will try that at the next opportunity Fabio, and let you know the result.

Dave

[Dave_S]

While using the native driver in Sharpcap, I can save the image in FITS format, and of course read the FITS header. A gain setting of 100 is shown it FITS header as 100. No problem.

When I choose ASCOM, The only option is 12 bit mono, the only format option is PNG. Thus the image is saved as a PNG file. No FITs info.

I guess, I will work with my intuitive guess, and transpose the Sharpcap gain settings into AA8/ASCOM, divided by 100.

As the point at which the read noise drops sharply is around Gain 900 (Sharpcap scale), see attached sensor analysis graph, I will set the gain in AA8/ASCOM at 9.

Of course, you could also include a sensor analysis function in AA8

[Jacmac]

I hope to be helpful by posting the link that seems to clarify

https://forums.sharpcap.co.uk/viewtopic.php?t=879