2" 38mm SWA 70deg Eyepiece with f4.76 Newt ?

[gfletcher]

Hi Guys

Has anyone any views as to the performance of a 2" 38mm SWA 70deg Eyepiece with f4.76 Newt ?

I am awaiting a Rigel 38mm SWA 2" eyepiece for use in my 80ED and perhaps for widefield views with my 250PX..

Graham

[John]

I reckon it will work OK but there will be some astigmatism in the outer 25% of the FoV with the 250PX and the exit pupil of 8mm will be larger than your dilated pupil so not all the light collected will make it into your eye. It should still be a nice wide field "sweeping" eyepiece though.

[gfletcher]

Thanks John

I have a Baader MPCC , would that help if attached to the eyepiece when using the Newt?

Graham

[andrew63]

I came across this a few days ago when looking for some low power ideas. I would think that the rigel would perform very similar to the Q70.

http://www.astromart.com/articles/article.asp?article_id=624

andrew

[John]

Thanks John

I have a Baader MPCC , would that help if attached to the eyepiece when using the Newt?

Graham

The MPCC corrects coma which is produced by the newtonian optics. Astigmatism is produced by the eyepiece rather than the scope. The irony is that you invest heavily in eyepieces like Naglers etc that can perform without astigmatism in fast scopes and you then start to notice the coma more - which is where the MPCC comes in

This web page explains and illustrates these two issues (and others) quite well:

http://www.umich.edu/~lowbrows/reflections/2007/dscobel.27.html

[Bart]

great link, John. Thanks

Bart