Quote:
Originally Posted by Larryp
That's superb, Dave  |
Thanks Larry
Quote:
Originally Posted by Peter.M
This is an amazing image, congratulations.
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Thanks Peter!
Quote:
Originally Posted by alistairsam
That's incredible Dave, looks fantastic.
How did you settle on 60 min subs and why opt for 2x2 bin?
would 1x1 have provided finer details? just curious.
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Thanks Alistair! My scope and camera are both fantastic on their own, but unfortunately they're poorly matched. Peter's point about image scale is spot on, especially as my seeing is 3-5''. Sensitivity is also an issue - according to ideal CCD exposure calculators, at 1x1 binning I'd need 30 min Luminance and 80-120 minute Ha exposures... not practical!
I starting using 2x2 binning to speed things up a bit, but then found the histogram was still bunched up on the left using 20 min subs. I tried 60 mins subs (the maximum for my camera) and found that the sky background was still extremely dark - 0.7% sky background with no moon - so I stuck with it.
Ideally, I'd pair this camera with a scope of around 700-800 mm focal length - but I haven't been able to find one that has a reasonably large aperture, is mechanically and thermally stable, has ample back focus for adaptive optics, and is cheap. For the $700 or so I paid for my GSO RC8 CF (used), I'm very happy with the image quality
Getting round stars with 60 min subs was easy using adaptive optics (0.5 & 1 sec guide exposures), even under windy conditions. I think I discarded fewer than 5 subs in total due to tracking errors to get these 86 subs?
The main downsides of 60 min subs is that you need a
lot of data in order to use more advanced data rejection algorithms like sigma clip and linear fit, and you get a
lot of cosmic ray hits. The stacked panels were terrible at 5 hours/panel (visible artefacts), but once I reached 10-15 subs the noise cleaned up and the really faint nebulosity started to pop.
Hope that helps!