Quote:
Originally Posted by Stephane
Thanks for the responses! I've done a series of little experiments which clearly indicate that the OAG, camera, and CC are not causing the artefact, but rather light coming into the tube (not a light leak though as the artefact disappears when the tube is covered even in broad daylight).
Dennis, I've determined that it is not a light leak, but perhaps an internal reflection? Any suggestions for identifying the origin?
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Hi Stephane
I assume the corrector is anti-reflection multi-coated to minimise any internal reflections from the optical elements?
If so, are there any other exposed reflective surfaces or components in the optical train whose profile might look like the unwanted artefacts?
These can be vexatious problems to track down.
Cheers
Dennis
EDIT:
I forgot to ask about the length of your Flat Frame exposures. I read somewhere that certain CMOS sensors can be non-linear with Flat exposures of less than 2 seconds. The advice was to take Flats of at least 3-5 seconds (Histogram peak around 30-50%) and then take equivalent Darks (i.e. 3-5 secs) for those Flats then Dark Subtract them from the Flats. This will give you a say 5 sec Flat Frame calibrated by an equivalent 5 sec Dark frame (same Gain, Offset, Temp.). I guess you could call these Flat_Darks as the Flat came first and the Dark followed it to calibrate it.