Quote:
Originally Posted by ericwbenson
Hi Allan,
I swear I had this conversation in an astro group a decade ago...I just can't find the email trail or yahoo group thread. As I recall the answer was it might help a bit with resolution, however the many artefacts it could be produce might nullify the gain.
A few obstacles I can think of off the top of my head:
-funny diffraction spikes caused by the shutter
-changes to the flat field i.e. star/bgd in middle gets more light than near the edges, unless using an sbig type sweeping shutter, which is btw usually slower than the iris types, which leads to the next point:
-in highly variable seeing your shutter open/close overhead time will seriously eat into your duty cycle.
-dark current accumulation (and the associated noise). If your effective duty cycle ends up being 50%, you dark current wrt the light signal just doubled.
Best,
EB
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Thanks EB,
There are bound to be a few problems but I think the overall result
would be an improvement.
If your total exposure time was identical the lights would be perfect.
However the dark frames would be not matching perfectly as they
would be a little longer than a frame where no shutter was used.
It would be better to have a proper Iris shutter than the sweeping type found in the QHY9m.
I wrote to Craig Stark & he suggests I write to this forum here:
http://openphdguiding.org/
He thinks that there is some merit to it & it's actually an old idea that was never implemented as most people would just get a better mount.
I have yet to write to that site but I will soon.
cheers
Allan.