Halo Effect on Stars in NGC457 Image

[Roy]

Monday night I was trying out the imaging rig for the first time since starting to use ASCOM and Alignmaster, and I hate to say it but, the whole system worked perfectly from the word go: alignment, tracking, etc., until the cloud came in after about an hour. I decided on a simple target in a good position: NGC457, the Owl Cluster, however (there's always a 'however') when I examined both subs and the stacked images, there was a red 'halo' to the top right of the brightest stars (see enlarged crop below).



Any suggestions as to what might have caused it, e.g. a reflection off the OAG prism?

Roy

[RobertM]

Roy,

You might be right - can you determine whether the OAG prism is on the same axis and direction as the abberation ?

It also looks to me as if the focus could be a shade tighter.

Hope that helps

Robert

[Roy]

Hi Robert,

I was wondering about the sharpness of focus - I use the focus tool in APT. The other thing, the stars don't look perfectly round which might be another manifestation of having the OAG prism too close to the optic axis.

Roy