Which 8mm eyepiece?

[E621Keith]

I want to get an eyepiece for X'mas to replaced my damaged X-Cel. I planned to use it for planets with my SCT and DSO with my 80mm.

What are your opinion on these eyepiece?

Vixen LVW 8mm

Pentax XF 8.5mm

TV Radian 8mm

I already have a 3mm Radian in the short end and planned to get 17, 22mm LVW when I go to the Far East next Feb, so I guess it'll be a good idea to stick with either Radian or LVW.

I need to wear glasses, so the need for long eye relief rule out orthos or plossl at this focal length. My budget is around £120, so I can get new XF if I shop around, but LVW or Radian will have to be found used.

Thanks for your advice.

[NGC 1502]

Can't comment on the Pentax, but I have the 8mm LVW ( also 13 & 22 ) and

2 Radians, 10 & 18mm.

The 8mm LVW ( and the others ) is a very nice ep, no eye placement or blackout

issues. It's a tough call between it and a Radian. Some don't like instadjust, I don't

mind it, it's easy to stiffen it up, 10 min job. The only downside to the LVW is that

it is relatively large & heavy.

For me, I just love the 20mm eye relief that these all have, and prefer that to

greater FOV with less eye relief. But it's all a trade off, and what suits one may

not suit another.

Best regards, Ed.

[sixela]

Tough call. On axis, the XF is actually the better of the lot, but if you want to use the entire field in some scopes you won't like the amount of field curvature if your eyes do't accommodate well for focus, and it will require a different focusing discipline (i.e. focus a star somewhere closer to the edge and everything will seem in focus, focus something in the middle and the edges may seem out of focus).

But that's for DSO usage. For planetary usage, I prefer it over the other two (Pentax lens polishing quality and coatings are really very good, closer to what Nikon and Zeiss can do than what Televue and Vixen can in Japan).

Actually, if you want this for planets, you should take a look at the not enormously expensive XF zoom, one of the few zooms that can replace a range of single eyepieces without loss of image quality (yeah, a €800 Leica zoom is better as is the old Pentax SMC 8-24mm, but even the latter one is a lot more expensive).

Amalia von Allmen's report is certainly worth a read; it's consistet with my (much less thoroughly quantified) experience:

http://www.cloudynights.com/item.php?item_id=1438

[E621Keith]

Thanks for the information, it sounds like all three are very good eyepieces. I guess my decision may simply depend on which turn up first on the used market.

I'm surprise the zoom can rival the primes in quality. I've always assumed the complexity of zoom design always degrade image quality. Unfortunately, the XF zoom's eye relief of 11-15mm is a bit short for me and the XL or XW zoom are well above my budget, but thanks for the suggestion.