Satellite trails in images : What do you do ?

[Catanonia]

Now I am taking many hours worth of subs, 5 mins each sub, i usually get satellite trails in a few.

What do you do with them

If i have 1 or 2 in 60 or so subs, they tend to disappear with DSS if i leave them in the stack, but I tend to remove them.

But what do you experienced guys do with subs that have sat trails in them ?

[Ben Ritchie]

Provided I have a reasonable number of subs I just sigma-clip the stack when I stack them, it's an effective way of removing satellites. Median combining works pretty well for smaller numbers of subs.

Put simply, sigma clipping drops pixels with 'unusual' values from the stacking process, so if a pixel is usually dark but in one sub it's bright because a satellite passed across it then the single bright pixel will be excluded from the stack.

If all else fails, there's always the Photoshop clone tool..

[roundycat]

SD Mask as implemented in Maxim places a standard deviation based mask over the set of pixels in a stack. If no outliers are found then the average value is used in the output, if an outlier is detected (typically from a sat trail) then the median value will be used. This gives the best of both worlds, a very quiet background and no trails in the output frame.

To work properly the number of frames in the stack has to be statistically meaningful, for SD Mask I find that 6-8 is a good minimum and I never throw away any frames, regardless of what 'damage' is on them. Even poor guiding can be sorted out provided you have enough good frames, say, for example, 6-8 good frames for every bad one.

DSS may be similar but I have no knowlwedge of it.

Dennis

[Psychobilly]

As already suggested use Median or Kappa-Sigma stackign dependign on the number of light frames you have...

There has been some debate as to whether your better off having more shorter frames or less longer ones...

I tend to use a mix of 300 and 480s subs at ISO800 and ISO1600 with the 1000D...

If were in for a decent spell of consecutive nights I try and get 2 hours of light on a target per night whilst the target is optimally placed for imaging...

If you grab the 300s frames at ISO1600 first this will give you a good idea of framing and whats there...

Peter...

[Catanonia]

Thanks guys, I have noticed that with Sigma in DSS they tend to disappear now. Thanks for explaining Sigma and Medium for me

/Cat hates throwing away subs, even if it is one out of 40