QHY168c Gain Scaling question

glauria
Posts: 23
Joined: Wed May 30, 2018 7:15 pm

Re: QHY168c Gain Scaling question

#31

Post by glauria »

Hi Robin,

I know that this is a rather old thread, but I thought I would revisit this issue to see if there's any more sense that I can get out of it. My 168c does not accept non-integer values of the gain. i.e., 1.6 won't work, but 1 or 2 will.

I thought I would retry the sensor calibration process to see if it the results made any more sense this time and found that it does! Now the gain values for the table make sense since they go from 0 14 (as QHY uses) instead of 1 to 100 as they did before. The table also agrees with the table that QHY publishes in that the unity gain value is at 10.

I also did the "factor of 10" reduction in exposure time as you instructed earlier in this thread and saw the same type of results as before in that as one decreases the exposure value by a factor of 10, the gain increases by that same amount. Here's my latest results:

Gain Exp. time
1 875 mS
9 87.5 mS
84 8.75 mS
> 255 0.875 mS

Here's the latest sensor analysis table results that now make a lot more sense:

Gain Value e/ADU Read Noise (e) Full Well (e) Relative Gain Rel. Gain (db) Dynamic Range (Stops)
0 2.99808254966626 3.33200235418101 49120.5844937321 1 0 13.8476506871995
1 2.80463859217046 3.29073107099304 45951.1986941208 1.06897286446668 0.579333618451362 13.7694067463942
2 2.6074841943917 3.23523590299004 42721.0210409135 1.14979893497137 1.21243804069087 13.6887875949532
3 2.40964363502603 3.17429070398395 39479.6013162665 1.24420163466781 1.89781535191154 13.6023855430539
4 2.21402719992694 3.11774698265483 36274.621643603 1.35413085700356 2.63321269213108 13.5061690936811
5 2.01758642981219 3.06646651523483 33056.1360660429 1.48597477925411 3.44022876825263 13.3960532799866
6 1.8198437275965 2.9987356256108 29816.319632941 1.64743955989336 4.33618980934167 13.2794602325984
7 1.62697321873069 2.94988546833994 26656.3292156836 1.84273626335735 5.30926364887679 13.1415315615272
8 1.43296709602616 2.89161099256186 23477.7329012925 2.09222009212941 6.4121473684324 12.9871320025598
9 1.23815402683498 2.81998829122992 20285.9155756643 2.42141323671182 7.68137824326659 12.8125016250564
10 1.04217356733096 2.73146344051921 17074.9717271504 2.87675934570521 9.17807065314383 12.6099214559396
11 0.928939952185809 2.91221622723654 15219.7521766123 3.22742341161205 10.1771189006659 12.3515397699301
12 0.662122419324165 2.6182826678581 10848.2137182071 4.52798827251075 13.11810586718 12.0165490276457
13 0.461403184361059 2.51406689231911 7559.62977257159 6.49775001838781 16.255259982829 11.5540768295203
14 0.262078275803539 2.426870599235 4293.89047076518 11.4396454283517 21.1682512742858 10.7889724898101

...now if I can only understand how to translate the 1 to 14 true gain values into the 1 255 range that's shown in the Image Control menu to find the unity gain value.
User avatar
admin
Site Admin
Posts: 9077
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY168c Gain Scaling question

#32

Post by admin »

Hi,

yes, those values look perfectly reasonable, so I think you have a good result for the sensor analysis there.

I am a bit puzzled about the 'image control menu' - not quite following what you mean there, or where the values of 1..255 come from.

cheers,

Robin
glauria
Posts: 23
Joined: Wed May 30, 2018 7:15 pm

Re: QHY168c Gain Scaling question

#33

Post by glauria »

Hi Robin,

My apologies for not being clear enough in what I meant by the Image Control Menu. I attached an image file of what I meant that's shown in SharpCap. What I'm referring to is that the digital gain goes from 1 to 255, and it would be great if it went from 1 to 14 so I can directly match it to the way QHYCCD displays it and is now shown in the Gain column of the sensor analysis results.

Thanks,
-Gene
Attachments
Image Control.JPG
Image Control.JPG (18.26 KiB) Viewed 56 times
User avatar
admin
Site Admin
Posts: 9077
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: QHY168c Gain Scaling question

#34

Post by admin »

Hi,

ah, right, I understand now...

Yours is one of the small selection of QHY cameras that have individual Red/Green/Blue gain sliders - these will have the range of 1 to 14, and you should use these as your primary gain adjustment.

The digital gain is a simple multiplier that can be used for things like target finding, but should not be used for actual imaging. For imaging, set this to the minimum value, which should (I believe - I haven't got a camera like this to test), turn off the digital gain effect.

Hope this helps,

Robin
glauria
Posts: 23
Joined: Wed May 30, 2018 7:15 pm

Re: QHY168c Gain Scaling question

#35

Post by glauria »

Thanks Robin!

This makes a lot more sense. I'll give it a try this tonight and see how the camera behaves. I've been keeping the digital gain at 100 and it may explain why the colors of my stars always seem to be washed out.

-Gene
Post Reply