Eyepiece and filter Qs.

[Solanum]

Firstly, my GSO 10" Dob has a 2" focuser, but my eyepieces are 1.25" (with adapter). What are the essential differences between using 2 or 1.25" eyepieces? If I have a 9mm 2" and a 9mm 1.25" eyepiece are they the same magnification? If so, is the exit pupil size different, making the 2" easier on the eye? Is the field of view different? Please feel free to point me to a thorough online article on this if it's easier.

Secondly, I want to get a couple of filters (polarising for moon viewing), can 2" filters be used with 2-1.25 adaptor or do I have to get 1.25" for the eyepieces I have (although I have a 2" barlow).

Thirdly, can anyone recommend an online store for reasonably cheap filters?

[rmcpb (Rob)]

2" eyepieces are only really useful at the lower magnifications where the field of view becomes too wide for a 1.25" eyepiece to allow the cone of light to pass. Simply the 2" allows a wider angle cone of light to enter the eyepiece.

Dunno about the 2" polarising filter, I just move mine from one eyepiece to another when I am using it remembering that you really only need it on the lower power lenses. Higher power lenses cut the available light down so a filter in the adaptor would be a bit of a pest in my view.

Try myAstroShop, Andrews or Bintel as starters for online purchases.

Cheers

[astro_nutt]

If using 1.25" EP's..use the same size in filters..as Rob suggests use the 2" EP's on low-mag targets like Carina or 47Tuc.
For information on filters see..
www.lumicon.com
www.astronomik.com
Cheers!