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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