Iris and Ghost re-process

[Mike]

Sounds like the camera has shifted under its own weight towards one of the corners to me.

[Carole]

That's the conclusion I came to.  I must take a look at the subs done with the same set up also done pre-flip.

Carole

[MarkS]

Sounds like the camera has shifted under its own weight towards one of the corners to me.

I think it's slightly more complex than that.  I think the top left and top right corners are equally affected by the "tilt" (if that's what it is - as you say, probably shifting under its own weight).  However it seems there is also a very slight elongation of stars over the complete field (possibly a slight guiding issue).  This elongation is is the same direction as the elongation of the stars in the top right and so the effect is additive making it more pronounced.  But this universal elongation acts in a different direction to the "tilt" elongation of the stars in the top left thus causing them to be elongated in 2 different directions and therefore they become almost circular again.  An analysis shows that the stars in the top left have a higher FWHM (or bloat) than the stars in the rest of the field of view.

I wish I hadn't started this!

[Mike]

That Atik weights nearly 1kg, with the weight of the filter wheel as well it will be well over 1kg so it will need a good strong focus unit to hold it perfectly still all night long.

Like Chris says, it's best to check the subs from time to time as you go along

[Carole]

Olly was having trouble with guiding at some points during the week as PHD kept pinging but most of the time the stars appeared to be round so we decided to ignore it as we couldn't fathom out what was going on.  This was the 2nd guiding set up we used as the Lodestar was having connection problems and we had to swap the whole guiding set up + use an extra computer as there were no drivers for the Atik guide camera we were now using.

I normally do check my subs (when I am at home and networked) as I go along and any dodgy ones get removed.
I am not sure how I missed this, I think I generally tend to look at the stars in the centre of the image rather than the edges, and thinking they were all OK I didn't re-check when I did my re-stack and process.

I guess I'll have to re-stack and process it again when I get time using the post-flip luminance subs.

Carole