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Best gain offset for using 12 nm. Narrowband filters

Bella123
02 Nov, 2019 20:57
Hi everyone, I use optolong 12 nm. Narrowband filters for my qhy163m, I was wondering should I use a lower gain and offset for these filters due to their, wider bandpass as supposed to say 5 or 6 nm. Filters ,also what is a good recommend gain and offset for these filters, using them on an f6 60 mm Astro tech Ed doublet. Any help would be appreciated. Thanks! Shawn.
jrista
05 Nov, 2019 19:03
I would only use a lower gain if you feel you clip the stars too much. Usually you can handle some amount of star clipping and once you stretch the data, unless you use more exotic means of stretching (i.e. a masked stretch or exponential stretch), you won't be able to tell the difference between the stars if they were clipped, vs. just highly saturated.

I recommend using Unity Gain for NB at f-ratios of f/4-f/6. I would use "half unity" (Gan 76 on ASI) for scopes faster than f/4, and "double unity (about Gain 200 for ASI) for scopes slower than f/6, just as general starting points. You should adjust as necessary based on how you feel about star clipping.
Bella123
05 Nov, 2019 22:08
Thanks John, I will try your advice, as soon as I'm able to see the stars again!
Bella123
05 Nov, 2019 22:47
Hi John, by the way  do you know what unity gain is on the qhy 163? I can't seem to find out what it is there is only a dso preset, but it seems to high to be unity gain.
HH_Astro
07 Nov, 2019 02:49
By the way- I did a test by capturing an image with gain 10 and one with gain 163 with my ASI1600 and found very little difference in the image…
Bella123
08 Nov, 2019 17:05
I have noticed the same thing, there doesn't seem to be much difference in gain settings on my qhy neither, I just mainly use the preset gain/ offset.
jrista
10 Nov, 2019 22:33
QHY has had different gain settings at different times. I think originally it was 1-50, then 1-500, now I think it is 1-50 again. The ZWO cameras are 1-600. Gain 139 is unity on the ZWO, so I would assume a gain around 11-12 is probably where you will find unity on the QHY.
 
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