HenrikBA

Thanks for your comments, I've now got the ES 17mm 92 degree, and it fouses with no problems in my 45 degree prism in the TV-NP101, still several mm of headroom. Very nice eyepiece, weight is no problem at all on TV-NP101.

Thanks a lot for your comments, I think I can balance the scope by moving my long dovetail forward in my Manfrotto videohead. The Nikon is very heavy too, there's still some headroom there. I was told in another forum that the ES 17mm 92 deg focuses around 13 mm further out than the Nikon NAV-HW 17mm, so I think it might just about be possible with my 45 deg erect prism.

If anyone has an ES 17mm for sale, I might be interested.

Now I've read so much good about the Explore Scientific 17mm 92 degree, so I'd really like to get one, if I can use it with a 2" 45 degree erecting prism. I use a TeleVue NP101 refractor mainly for birding; it's a brilliant telescope, but it has very limited in-focus, probably due to the Petzval design. My preferred eyepiece is the Nikon NAV-HW 17mm, which I can't use with my 45 degrees prism. I bought a 90 degree APM prism with very short optical length, but even that was not possible to use with the Nikon NAV-HW, until I made a modification to move further down the eyepiece. Also the APM 20mm 100 degree eyepiece can't focus at infinity with my two 45 degree erecting prisms. As 45 degree is often nicer to use for terrestrial observation, I'd really like to get a 17mm super wide angle eyepiece to use with my prism, so I'd like to hear if anyone in this forum knows, if the ES 17mm is less critical to limited in-focus than the Nikon NAV-HW (which I can't use either with the 14mm ec) and the APM 20mm? Most other eyepieces I have will focus all right with my 45 degree erecting prism. Henrik.