Eyepiece designs & focus position

[MortonH]

I've noticed that my Televue eyepieces all require the focuser to be racked out much further than my other eyepieces. No big deal really.

However, with my ZS80 and new 2" 45-degree erecting diagonal, my TV eyepieces are the only ones that will reach focus at infinity. For my other eps, there isn't enough in travel.

Anyone know why TV eyepieces reach focus at such a different point from other brands? And are there any other eyepieces that are similarly weighted towards back focus?

If I keep this scope, I need an eyepiece around 20mm focal length to 'replace' my Pentax XL 21mm, which won't focus at infinity. I might consider a 19mm Panoptic, but the eye relief is only 13mm (compared to 20mm on the Pentax).

Anyone know of cheap-ish eyepieces that might work?

Morton

[dannat]

you could try a 20mm WO swan. Are all the TV ep's the same from nagler's to plossl's?

[MortonH]

A Swan is the prime contender at the moment, if it works. I don't know about TV Plosls, but I've used a few eyepieces, including Panoptic, Radian, Nagler zoom and 8-24 zoom, and they all seem to require more out travel on the focuser than anything else.

If only the WO diagonal had a zero-height 2' to 1.25" adapter!

Morton

[Dennis]

Have a look at this “negative distance” adapter from Scopestuff (http://www.scopestuff.com/ss_npea.htm).

Cheers

Dennis

[MortonH]

Thanks, Dennis. Bit pricey to ship from the US, but probably cheaper than a new eyepiece!

I know that GSO diagonals come with a zero-height adapter, but the main 2" barrel has a cut out to allow the screw of the adapter to pass through. The scope stuff adapter has found a way round that, I guess.

Morton