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20mm EWA eyepiece


The Warthog
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I bought this eyepiece at a star party last year. It has a nominal AFOV of 66 degrees, and that is probably accurate. I timed a star in the Pleiades crossing the FOV at 7 minutes 30 seconds. This was at 37.5x. The thing I noticed about the image as the star crossed the FOV, though, was that the image degrades seriously towards the edge, turning into a smear as it progresses towards the edge. The star resolved into a point 2.5 minutes after I started timing the crossing, stayed focused for 2.5 minutes, and then smeared out for its last 2.5 minutes. That means that the clear, focused area of the AFOV is actually 22 degrees across.

I'll have to pay more attention to some of my other eps, but I know my X-Cels are clear almost to the edge, and my 32mm Plossl seems to have a bigger 'clear' area than the EWA. I was a little surprised by the performance of this ep, as I have enjoyed using it. I captured M81 and 82 in it, and they looked gorgeous. I suppose you spend more time looking at the centre of the FOV anyway.

I paid $33 for it (star party price and a little haggling) but I have seen them going for $60. This particular one was branded "Knight OWL" which is sold on eBay. For $33 it wasn't a bad purchase, but $60 is getting a little high for this kind of performance. These are offered under other brands as well. It has good eye relief and is very comfortable to look into. I'm not going to throw it away soon, but it is on the list to be replaced in the next year or so.

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It was in the Newt. I can't remember if I've used it in the refractor, though I probably have. I went out a little later to play with a couple more eps, but fog had settled in, and although there were still stars at zenith, it wasn't worth the effort.

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I think you'll find that this eyepiece will work much better in your refractor. I used to have one of those and it was not too clever in my 8 inch f5 Newtonan - "seagulls" all over the place !!, wheras in my f10 4 inch refractor it worked nicely and I used it a lot.

Shorter focal length scopes (ie: f6 or less) are quite unforgiving on eyepieces. Because I could not afford Panotics or Naglers (which are designed to give sharp images right across the field even at f4 !) I stuck with good quality "standard" field eyepieces with my Newt - Tele Vue Plossls and Celestron Ultimas are pretty good I found.

John

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  • 2 months later...

Well, John, talk about being right! I put this eyepiece in the f/9.5 refractor tonight, and found it delivers edge to edge sharpness in this scope, and more FOV than I can really use. It's definitely a keeper when combined with the refractor.

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Well, John, talk about being right! I put this eyepiece in the f/9.5 refractor tonight, and found it delivers edge to edge sharpness in this scope, and more FOV than I can really use. It's definitely a keeper when combined with the refractor.

Thats good news WH !!.

John

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