Spot the difference

Yea, you are getting at lot worse at this imaging lark

:oops: I'd better spend that 20k on anew OTA/CCD combo then or you'll never let me live it down...

Eirik may be ablt to better processing than I. Of course, if anyone out there wants the 40 or so raw FITS...

Dave --

I've never done any imaging at all, so you'll have to take all this with a grain of salt. But I have managed to collect a few tidbits on star shape:

• Bad seeing makes the stars bloat as the direction of movement is entirely random and over time will occur in all directions.
  
  
• Mechanical errors (whether PE, snagged cords, floppy mirrors or miscollimation) normally exhibit elongation or streaking all in the same direction. Your update to M57 seems to show a bit of this -- note that the stars are all sligthly wider than they are tall.
  
  
• Optical errors are usually symetrical around the axis (the center of the image, assuming no cropping). Your update to M13 appears to show something on these lines -- notice that the elongation in the corner stars generally points out from the center. I don't know if that's field curvature or coma, though (and I'm a bit surprised to see it with both a focal reducer/flattener and a reasonably small chip).

As for the results, I'm with the crowd. I like last year's M57 slightly better but this year's M13 _much_ better.

-- Jeff.

I'd second what the guys above have said.

Ont thing I discovered over the past few years with deepsky imaging, is that just because its bright doesnt mean its easy, I've found that globulars are the most difficult deepsky objects to get right, focus and tracking errors stand out a mile with them.
The zoomed in globular image shows coma towards the edges, this gives you the warp factor effect.

You know, on your Ring Nebula one, I prefer the one from last year! It has more stars in the field, and the nebulosity is not as, well, boosted! Your new one has less stars, but looks like the gain on the nebula is higher.

1st M57 for me, I'm afraid!

Yea, you are getting at lot worse at this imaging lark

Dave - I can lend you some of my green lens cheese if you think that might help I reckon the before shot of the ring is better. You can't see the spiral galaxy at all in the second. You produce some fabulous monochrome images - when are you going to treat us to some colour? I know processing in colour is a b1tch, but you got to try some time - with your set-up I'm sure you could produce some fabulous colour images.