Egg shaped stars

[Glenhuon]

I have been improving my guiding and focussing of late, but notice that the stars out towards the edges are still egg shaped in the images. Is this an inherent problem with reflectors or just a problem with my mirror. Would some sort of field flattener help.

Cheers
Bill

[bmitchell82]

Well if it is the 250mm dob that your using then the answer is yes, its to do with the hyperbolic nature of the mirror that light hitting the outer 1/3 of the mirror focus's at a different part.

If your doing photography i suggest you invest in a 250 dollar MPCC (Mulit purpouse Coma Corrector) this will clean up the image and is designed for newts with a f# between 4 - 6 with f5 working the best.

Good luck

[Glenhuon]

Thanks Brendan. I thought it would be something like that, but had to confirm it. Using the 6" F5 so the Baader one looks ideal, just ordered one from MyAstro.

Cheers
Bill

[Gama]

You have the normal coma thats inherent in many types of telescope.
The flattner will fix this.

Theo

[Bob Jones]

Hi Bill

Can't see a Baader field flattener on my Astro website. :eyepop:
Did you mean to say Williams?

I'm also looking for a field flattener solution to Coma in my Orion EON 80mm F6.5 (focal length 500mm)

Cheers
Bob Jones

[Moon]

Bob

Here it is:
http://www.myastroshop.com.au/products/details.asp?id=MAS-221

You can also get it here
http://www.andrewscom.com.au/site-section-10.htm


For the Orion EON 80, prehaps try something like the William Optics FF II / (P-FLAT2) ?

James