Any ideas what this is??

[daz]

Blue filtered sub from part of M45 the other night. The Clear, Red and Green are fine....

This is after a fairly gentle stretch in PS ....

[barkis]

A Waffle? I presume you mean the grid on the really bright star?

Looks like multi diffraction spikes, are you using your Newt?

Sorry for the three questions. I know it's rude to answer a question with a question, but three is past a joke.

Ron.

[jgs001]

Dunno, could it be some form of dirt on the blue filter causing and odd diffraction pattern ??

[daz]

Yes, the grid on the stars

No, ED80 refractor

A waffle........

The blue filter from the M101 subs shows no such pattern....

I'll double-check they are clean, but I wonder if its some sort of reflection - but then why doesn't it show on the the others....

[Mikea]

Intriguing! I read something about difficulty of accurate focussing across blue wavelengths. I'll keep looking!

[Tim]

Probably only the stars in M45 are bright and blue enough Daz to show up the problem.

[daz]

Could be Tim

I'm not overly fussed - it wasn't a real image, but was surprised when I stretched it and out came the waffle!!

@Mikea - thanks

[Whippy]

I've had similar on occasion but on noisy, faint areas after some agressive stretching. I put it down to something DSS is doing with subs of a particular type or rotation, something like that.

Tony..

[Mikea]

But why does it only appear on blue?

BTW, the thing I had seen related to Bahtinov mask spikes with blue filters - not relevant here - sorry!

[FraserClarke]

Was the data flat fielded? I've seen similar patterns to this is the flat field pattern in the blue on some high-end CCD chips. Would be quite surprised if you say it in data though...

It also looks a little bit like the artifacts you can get if you do some funky fourier transforming on the data to try and get rid of/enhance certain spatial frequencies. Did you run any sharpening routines on the data? Maybe they run a fourier transform, and you're picking up the resonances from the saturated core of the bright stars??