If you feel like using the sensor characterization routine in SharpCap, it will
give you a valuable amount of information on gain vs exposure vs sky condition.
Sent from my iPhone
On Jan 24, 2019, at 8:40 AM, Michael McDonald <mikemac@xxxxxxxxxxx> wrote:
I finally got my mount somewhat aligned last night. But it was too late for
me to do anything serious so I mucked around playing with M45/Orion. I
noticed that APT has a parameter for Gain that I had set to 1 for my ZWO
1600MM cooled. So I played around with it a bit, after a deadens of mucking
with the same parameter in the ASCOM driver. APT overrides it so changing the
ASCOM version didn’t have any effect. That’s when I noticed the APT version.
Anyhow, I tried 30 second (unguided, PHD2 and I are still working out our
relationship!) with a gain of 1, 100, and 300.Boy! At 300 you get all sorts
of nebulosity. Almost looks like one of those photos you see on the
astrophotography sites! (Burned out center and all!) But the background is a
medium grey instead of black and it seems noisy. At 100, you get just a bit
of the central nebulosity but nice black skies with little visible noise. At
1, which is what I’ve been using by default, there’s just the slightest hint
of the nebula. Just enough to indicate that there’s something there if you
took a much longer exposure.
I believe that there’s a tradeoff with increasing the camera gain in that it
also increases the noise. It doesn’t appear that gain is linear from my 3
data points. 100 seems much closer to 1 than 1/3 of the way to 300. That
could be due to the way eyes work though.
So my questions:
1) Short of doing a full scientific characterization of my camera, (I’m doing
this for “fun”!) what’s a good spot/rule of thumb for an initial setting for
the gain parameter?
2) Is the added noise from a high gain random enough that it’ll (mostly?)
cancel out when stacking multiple images?
3) Do I need to make my dark frames etc with the same gain setting?
4) What else should I be aware of when it comes to mucking with “gain”?
Mike McDonald
mikemac@xxxxxxxxxxx
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