Lovejoy with FSQ


#1

Managed to get a halfway decent Lovejoy image. This was with 2.3 and older PhD and SBIG API as I have not been able to get PhD to do anything but crash with the newer versions (see thread here and PhD forum for that).

Cycle thru events and delays were helpful in putting enough time between exposures to make rejection work pretty well and still keep timing consistent enough to use PI comet script.

Lovejoy from 1-13-15.

Paramount ME
FSQ 106
STT 8300

Stars RGB, Comet LRGB

Stars 240 seconds x 6 each color
Comet Lum x 45 seconds x 15
Comet RGB x 60 seconds x15 (each)

Processed PI and Photoshop CC 2014

Lovejoy


#2

Nice! So are you tracking the comet with custom rates in TheSky? I’ve had good success tracking using Horizons (APCC) but not so much in the post processing phase. I’ve had better luck just stacking the calibrated images than trying to align then comet align, as it seems the workflow for cometalign is generally geared toward sidereal tracking. I think maybe cycling as you’ve done might help w/ rejection.


#3

No, I tried that as well as a guide scope tracking on the comet nucleus. The secret, if there is one, is to set things up so that the comet script in PI has the best data to work with to reject stars. That means having decent separation of the stars between each individual exposure so that the comet script rejects the stars effectively. A combination of delays between exposures and cycling through as opposed to finishing filter events gives that.

Works on a bright comet, as exposures can (barely) be short enough not to smear the comet too much. Would be hard on a dimmer or faster moving comet.


#4

Thanks for sharing your technique - I had a quick go myself but alas without researching it first - I’ll know for next time…in 8000 years!

I didn’t realise PI had a comet tool. I hope it has some documentation.


#5

It is a script. Basically you need a series of shots tracked on the stars but not long enough to significantly smear the comet. You calibrate and register as usual and then load those files into the comet tool, marking the position of the comet on the first and last exposure. It then knows the path and time scale of comet movement and generates a new set of “comet registered” files which can be integrated to enhance the comet and reject (most of) the stars. You will probably need to make the sigma high value quite low to get decent star rejection. It is not perfect, but with some added editing in Photoshop, seemed to be pretty good.

Theoretically you could use the first set of registered images to reject the comet and use for the stars but I have found that does not work well so elected to do separate shots of the same area another night, sans comet, for the stars.


#6

Thanks for that - I found the tool - managed to get a really nice comet from my exposures in SGP, with a small head and a detailed tail but as I had not separated the stars with enough elapsed exposure, the background was distracting. I’ll know for next time.


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