Quote:
Originally Posted by Rhino1980
May I chime in and also ask for an Ethos reccomendation? I have a 10 inch Skywatcher Newt and am tossing up between a 13 and 17 Ethos. I mainly like DSO observing and don't really care much for planetary stuff.
Cheers and sorry for hijacking, just didn't want to start another clone thread
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Either one is fine depending on how much true field and exit pupil you want. The 13E gives you 1 deg at 96x and 2.6mm exit pupil and the 17E gives nearly 1.4 deg at 74x and 3.4mm exit pupil (both 1250mm f.l.). If you have another low power eyepiece such as the 31 Nagler then go the 13 otherwise the 17 or 21E. Note the 13E is 1.25/2" and the 17E is 2" only in case it matters for any filters that you may have. You can add a Tele Vue EBX-2120 to convert the 13E to 2" and then use 2" filters but you cannot use 1.25" filters with the 17E.
The 17E or 21E would be better for larger objects such as Eta Carina nebula and truely spectacular when combined with a 2" O-III filter.
See
http://www.televue.com/engine/TV3_page.asp?id=89 for more combinations of telescope and eyepiece.
Note at f5 you may also consider a Paracorr in which case your magnification wil increase by 1.15x and your true field will decrease by the same factor.