Some green tinted stars and oval stars

[scadvice]

I'm trying to nail down what causes this. Some of the smaller stars have a very, very slight green tint to them and some are oval shaped. Looking at the finished image however, the larger and mid range stars are round clear out to the edge. Any thoughts on this??

Edit added...This is a near full sized imaged, centered and only minimally cropped.


This leads in to another question... What is the best way to give access to a stacked TIFF file on here since they are pretty big?

30 sec x 83 @ iso800
20 darks
20 bias
20 Flats
Canon T3i mod.
Moon 93.5% illumination. (the glow in the lower right of the image)
WO GTF 81 Five Element APO Refractor, guided with a Altair GP130M on a WO 66mm Zenith Star Doublet Refractor.

[admin]

Hi,

Oval shaped stars can be caused by a number of things; poor tracking, field curvature and/or not having the imaging place perfectly perpendicular to the tube. Given that the shapes vary a little I'm inclined to say it's a mixture of the latter two.

Google Drive, Dropbox and OneDrive are popular choices to share large files.

I'm not 100% sure what's causing the green tint, but it could be the stacker having trouble stacking the stars correctly - a common problem if field curvature is in the mix...

[scadvice]

Thank you Ivo That gives me some things to look for.

Steve