Need Help Deciding Which EP to Get

I’m looking to purchase a low powered EP and need help deciding which would work best for my 10” dob (1,200mm f/4.7). I was thinking about something between 30mm to 40mm. I generally view from a heavily light polluted area, but do attend monthly star parties where the light pollution is not as severe. Also, since I have a 2” focuser, should I get a 2” EP? The only problem I can see with getting a 2” EP is that I would have to get two sets of filters as I already have several 1 ¼” EPs. Any comments and or suggestions will be greatly appreciated. Thanks in advance and have a VERY MERRY CHRISTMAS! Aloha from Hawaii, Paul

Hi:

Choosing a 2 inch Widefield eyepiece for an F/4.7 scope really boils down to how much money are you willing to spend.

For slower scopes, F/10, there are some reasonable economic eyepieces but at F/4.7, it is pretty much the more you spend the more you get. The big issue is edge correction. A $90 80 degree 30mm is nasty in a fast Newt. Only the very center section is sharp, the astigmatism begins to show itself as you move away from the center and at the edge it looks like the Enterprise at Warp speed.

In general, the Orion Stratus line has gotten good reviews as combining a good price with good performance in fast scope, I have never looked though one.

At the high end there is the 31mm Nagler which will cost as much as your scope but is a good value on per-pound basis.

One thing to keep in mind when choosing an eyepiece for your scope is the exit pupil. A 33mm eyepiece at F/4.7 is a 7mm exit pupil so this is about as long a focal length as is reasonable. If your pupil doesn't open to 7mm, then yo are already losing light and often one's eyes show astigmatism which would otherwise go unnoticed with a large exit pupil.

So, the main question is: How much are you willing to spend, remembering that this eyepiece could be the last long focal length 2 incher that you will ever buy?

Jon

If you buy the Baader T-2 Click-Lock EP holder and put it on the Baader 2" T-2 nosepiece, you can use your 1.25" EP's with any 2" filter. This rig also holds binoviewers better than anything else I have tried.

It's best to buy all filters in 2" sizes if you have any 2" EP's and reduce down with a 1.25" adapter or Click-Lock when using 1.25" EP's.

You need a wideangle 2" EP so that you can have the widest FOV without encountering mirror blackout. Something like a 35mm Panoptic, 31mm Nagler, 34mm Siebert Observatory or 30mm Pentax XW are good choices. There are several others as well. One you should especially consider is the 34mm Observatory by Siebert Optics. I have the 38mm version which is a custom order focal length. This wideangle design is extremely comfortable with absolutely no kidney beaning or blackout problems, lightweight, small for a wideangle design and priced very affordably with a return privilege if you don't like it. At $200 it's going to come in well under the price of the others even if you bought them used. Downside is you will have to wait a few weeks for Harry to build it. Cheap 2" EP's probably will not work well at f/4.7. The 34mm Observatory will work well at your focal ratio. A 34mm Axiom will not, although I have a 34mm Axiom that on an f/15 Mak-Cass will outperfrom the Siebert Observatory a bit, though at a higher cost unless bought used. I bought the Siebert Observatory for very fast focal ratios and you will have a very hard tome finding them on the used market because the owners like them. Harry said that almost nobody wants their money back on the Observatory series EP's. They are outstanding wideangle EP's for Dobs without the cost and weight of the premium priced brands.

Phil