blue circles around stars

[graham.hobart]

Hello, I have gone back to my QHY 8 OSC as I have little time or the weather to do LRGB imaging currently. I actually really like the warm colours it produces through my Orion ED EON 110mm refractor, but a recent basic run through with some images and star tools showed up a blue ring or halo around the brighter stars.
Can anyone advise me of processing these or avoiding these- Star Tools mainly, but do have photoshop but am niave there!
Cheers
Graham

[graham.hobart]

And by the way just passed 900 messages on IIS since 2008 , wow how time flies!
Not the most prolific of posters then!
Cheers
Graham
NB will post a picture when home from worky

[graham.hobart]

is this a facet of chromatic aberration?

[multiweb]

It's likely not color corrected with the OSC because it's not an APO. Separate your channels and check the red or the blue. I bet one must be out of focus.

[graham.hobart]

It is labelled as an APO refractor, but I will check my levels
Cheers
Graham

[cometcatcher]

I bought a refractor once labeled as an APO. The CA was terrible. But we await your pics to see for sure. Does sound a bit like CA though.

[graham.hobart]

pics uploaded

[multiweb]

Ha sorry, should have read the scope specs. It is indeed an APO. Weird. Shouldn't do that then.
PS: had a look at your shots. The blue is indeed bloated compared to the red and the green channels so there is a slight issue with colour correction although not as bad as an ED doublet. I've seen worse (https://skydrive.live.com/?cid=6930D3AD12D5044C&id=6930D3AD12D5044C%21863#cid=6930D 3AD12D5044C&id=6930D3AD12D5044C%21871&v=3). Are you using any kind of field flatener ore corrector/reducer in the imaging train. That might come from other glass in the system.

[graham.hobart]

Marc- good call! I am using a hotech field flattener. If this is the cause then I think I will live with it as I prefer the blue stars to the field curvature on wide shots!
Thanks
Graham

[cometcatcher]

Yeah that's CA. I agree with Marc, the blue layer is bloated. It's not real bad though.

Sometimes the FF can make it worse. What focal length is your scope? Televue make one but not sure if would suit. Another option is to try the Baader Semi-Apo filter. It reduces the blue channel by 50% and boosts nebula as well. It does reduce overall light however.

The next thing to try would be to reduce the blue channel saturation in photoshop or whatever program you use.

[rcheshire]

I think you can use the halo reducer under filters in startools.

[graham.hobart]

it's 660mm f/6.
Good tip re Star Tools Rowland- will investigate further.
Cheers
Graham

[Shiraz]

as others have said, it will almost certainly be CA - APO doesn't mean no CA, it just means less CA (in general). Worth a look at the spot diagrams in fig 149 in http://www.telescope-optics.net/semiapo_and_apo_examples.htm - even the most highly regarded APO designs (eg Petzval, fluorite triplet) spray a little bit of energy out a fair way from the best focus, resulting in halos. A minus violet optical filter could possibly help remove the worst of it without messing up the colour much. I think the halo reducing filter in StarTools is called fringe killer - have never used it, but think that it attempts to remove and replace data that falls within a narrow spectral band.

Of course, you could just ignore it and accept that this is what your system does - doesn't mess up the image a whole lot.

regards Ray

[rcheshire]

Fringe Killer is the one. Masking the halos and operating on them without affecting the blue in the rest of the image might work.

[raymo]

I'm a newbie at Image processing, but it seems to me that your fringes
are due to over saturation of colour. You don't actually have blue haloes; you have haloes of whatever colour the star in question happens to be.
For example, the yellowish stars have yellowish haloes, and the blue ones have blue ones. Also this is indicated by the bulb like centre of the nebula
being much too strongly coloured.
raymo