Satellite & Asteroid Trails in Subs

[multiweb (Marc)]

Lately I have been exposing 900s subs and over in Ha. I also improved my calibration routine so now when I stack I can see a lot more things and details including all those pesky slow moving things like asteroids. What's the best way of removing them? I'm using Sigma reject 2% with 2 iterations max. Works well for fast flying objects leaving a clear trail but I've got problems getting rid of the slow moving ones that would translate maybe 5-10 pixels over an hour or so. That ends up as a dotted lines in my stack. And there's a lot of them too. Thanks for any tips.

[Bassnut (Fred)]

Healing tool in PS

[multiweb (Marc)]

Well PS is the last line of defence. There is actually something better than the PS healing tool. It's the "freehand draw" in CCD Stack. Then Impute Rejected Pixels prior to stacking. That's what I've been doing. My problem is that Sigma Reject on a stack will detect cosmic rays because they come and go but won't detect a slow moving object if the signal overlaps slightly from one frame to the other. It will treat it as a star "bouncing" in bad seeing and will keep a faint signal. So you end up with a faint line. Dithering doesn't resolve the issue because the position is relative to the stars. Just wondering what other CCD Stack users do.

[Bassnut (Fred)]

Well, being a CCD stack user, Poisson sigma reject may do it, but its aggressive and can leave artifacts. I found freehand draw and impute rejected pixels corse and a pain in the bum to get the settings right for anything other than obvious blooming, theres always a few bright pixels left over. Its always good to try and get rid of random stuff before deconvolution/sharpening, or artifacts just get rediculous, but after much stuffing around in CCD stack, PS healing really is the ducks guts, and gives the most control.

[montewilson (Monte)]

Get in contact with Mick from the ASNSW. He will have an answer.

[jase (Jason)]

Marc, the likely answer to your problem is to dither between subs. This is a commonly overlooked technique which can vastly improve the quality of the master. Alternatively, as Fred points out, you can chase it with the healing brush tool (this is a rather ghastly task IMO, but works) or use data rejection algorithms to your advantage. The latter assumes the outlier pixels are in different locations so the data rejection algorithm can detect the anomalies in each sub when you combine them - hence make sure you dither between subs!

[theodog (Jeff)]

Originally Posted by multiweb

Lately I have been exposing 900s subs and over in Ha. I also improved my calibration routine so now when I stack I can see a lot more things and details including all those pesky slow moving things like asteroids. What's the best way of removing them? I'm using Sigma reject 2% with 2 iterations max. Works well for fast flying objects leaving a clear trail but I've got problems getting rid of the slow moving ones that would translate maybe 5-10 pixels over an hour or so. That ends up as a dotted lines in my stack. And there's a lot of them too. Thanks for any tips.

Three Questions;
How do you identify the asteriods?

What equipment are you using to image?

The max. no. of asteriods I managed in one image is 5, and thats with carefull planning, are you sure that they are asteriods?