Blue halos around stars

[Geoff45 (Geoff)]

Have a look at the halos around the bright stars in these 5 pics.
1. William Optics 110mm refractor (APO)
2. 6" Newtonian reflector.
3 Meade LX200.
4 Stellarvue refractor
5. 88" RC (University of Hawaii)

With the refractors, you might be tempted to say that is was chromatic aberration, but since the reflectors show a similar effect, it may not be CA. I tracked down a couple of interesting articles which may throw some light on this issue. The essence of the matter is that they are probably due to internal reflections in the camera, that is, from the glass plate covering the imaging chip.
Have a look here and here
Geoff

[Garyh]

I thought the 6" newt one looked familiar..

I had always thought the halo was caused by my camera adapter and my focuser? looks like its more likely like you mention a reflection on the UV/IR filter over the chip..Interesting reads!
cheers

[Kal (Andrew)]

Very interesting read there Geoff

[ballaratdragons (Ken)]

Sorry I can't help, but I must say 'WOW! Great Images!!!!!

[Alchemy (Clive)]

makes you feel ripped off to spend the big bucks on sophisticated gear only to have reflections from glass.....

stick with the cannon for a while longer i think

[jase (Jason)]

Yep, been down this path. I typically get internal reflections when using the blue and green filters. As Don points out - to calculate the source of the reflections you can use a simple formula:

HD = Halo Diameter in pixels
P = Pixel size in microns
FR = Focal Ratio

(HD * P * FR) / 2 = a distance of X mm from the chip.

You'll need to know the mechanical measurements of your camera so you can work back from there. Internal reflections don't pose any problems and can easily be processed out.