SharpCap Forums

See the attached photo.....this is the resulting stack of 30 frames at 2 minutes each. Note that the brighter stars have curved lines emanating from the top and bottom. My setup was an Explore Scientific 127ED refractor with .8 focal reducer/flattener and Optolong L-Pro filter and a ZWO ASI2600MC pro camera. My stacking method was "Sigma Clipping".

Thanks, Mark

Hi,

several possibilities...

The most likely seems to me that the mount was disturbed during one of the early frames (while the sigma clipping was still being established and was therefore not able to deal with the problem). After disturbance the mount vibrated back to the normal position, leading to one frame with the stars being stretched out to lines (I see more line on one side than the other). If this had occurred after the first 10 (or so) frames then sigma clipping should have dealt with the issue.

Another possibility is reflections in the optical system, but these usually add curved arcs related to, but not through, the bright stars.

If the line trailed off in only one direction from the star, I would suspect a tracking issue, but that doesn't look right for it being both sides.

cheers,

Robin

Thanks Robin. I appreciate you taking the time to respond. If the mount had shifted as you indicated, wouldn't the curved lines be wider than they are to be more like the diameter of the stars?

Mark

Hi Mark

Are these lines showing also in individual frames?

Menno

Hello Menno,

Unfortunately I didn't save the individual frames. I'm going to do that when I get another clear night.

Thanks,

Mark

Hi Mark,

my thinking was that the shift was for a short part of 1 sub-frame (say 1-2s of wobble in whatever exposure length you were using - maybe 30s?). That would account for them being fainter and hence narrower (you would only see the brightest central part).

cheers,

Robin

Ah, got it. I'm hoping to get a clear sky tonight and do some additional captures and save each image.

Thanks Again!

Mark