Explore Scientific 92 deg LER 17mm

[25585]

https://www.firstlightoptics.com/all-eyepieces-barlows/explore-scientific-92-ler-series-2-eyepieces.html

I had pondered about this ep before plumping for the Nikon 17.5  ES is an unknown maker to me, and the 17's eye relief is 5mm less at 22, than the Nikon's 27.

However as the former comes at a specialist price with a 92 degree AFOV, has anyone got one or just tried it out to compare with other UWA eps?

[Victor Boesen]

I have a lot of the 82 degree eyepieces, and they are very good. Sharp across 90+ procent of the field of view.

[John]

I've owned and used some of the ES 100's, 82's and 68's but not as yet one of their 92's. I'd like to try one someday though

They seem to get very close to Tele Vue performance usually for a chunk less money although I note that the ES designs where they did the R&D legwork themselves are quite a bit more expensive than those where they copied an existing design.

 

[GavStar]

I own the 12mm and 17mm Es 92s and am extremely impressed by them. I've seen them described as Pentax xws on steroids and I think that's a good description. I find them very comfortable to use and much easier to view the full fov compared to my ethos 17mm and 21mm. I also see the stars crisp to the edge of the fov. When comparing to my ethos I can't see any material difference in the views. However I know some US observers think the ethos view is very marginally better. 

There are rumours that a 6.5mm, 8.8mm and 22mm Es 92 will be released at some point in the future. If that happens then I think some of my ethos will be up for sale.

Key downside for the Es 92 is the size and the weight - you need a good mount and solid focuser I think.

But in summary my favourite eyepieces for mono viewing of DSOs.

[Louis D]

I have the 17mm ES-92, and it is much better all around than the 17mm Nagler T4 which I still own but intend to sell.  It has a measured usable 17mm of eye relief compared to 14mm for the NT4 (and 18mm for the Delos, Pentax XL, and Vixen LV and 16mm for the Pentax XW).  It has no astigmatism or lateral color at the edge just like the Delos and Pentax XL (I'll have to check my XWs on this more thoroughly), unlike the NT4 which has slight amounts of both.  It has no field curvature like the Delos and 10mm and below Pentax XLs/XWs, unlike the NT4 which has some.  The exit pupil is not finicky, just like the Delos and Pentax XLs/XWs.  The NT4 is very finicky.  The moment you press in enough to see the entire field, if you press in a fraction of a millimeter more, you get tremendous blackouts.  If you pull back a fraction, you lose the field stop.  It's tiring to use for any length of time.  The 17mm ES-92 views like looking through a window by comparison.  The 92 degree AFOV exceeds the vertical height of my astro eyeglasses, but not left to right, so I can't imagine going any bigger.  Other than size and weight, it, like the Delos, has no imperfections to speak of.  It really does feel like a Delos on steroids.  If Nikon or TV made it, they would probably ask $700+ for it.  I intend to get the 12mm if they go on sale again at Christmas to replace my 12mm Nagler T4.

I am curious about the 17.5mm Nikon NAV-SW, but not enough to buy one for comparison sake.  I think some of the 27mm of eye relief is lost due to the eye lens being quite recessed even with the adjustable eye cup all the way down.

[John]

Interesting comment here on the ES 92's from Don Pensack, who knows a thing or two about eyepieces:

I only mention this because I know that the amount of useable eyepiece is very important to the OP.

 

[rl]

Agree entirely with GavStar and Louis D. IMHO these are the best eyepieces (at these focal lengths) ES make provided you can cope with the weight. Rumour has it they factored in gravitational lensing on the ray tracing program...

RL

[Louis D]

49 minutes ago, John said:

Interesting comment here on the ES 92's from Don Pensack, who knows a thing or two about eyepieces:

I only mention this because I know that the amount of useable eyepiece is very important to the OP.

 

I saw that as well, but rolled the dice with some trepidation, and found I have to barely press in.  Again, that 1mm difference in usable eye relief (17mm vs. 18mm for Delos).  It's actually less than the 2mm difference for the Pentax XW (16mm vs 18mm for Delos).  The NT4 are ridiculous at 14mm of usable eye relief.  Losing 4mm is just too much.  If ES could bring the eye lens up to be flush with the top of the housing, the ES-92 would be as comfortable as the Delos.  If your eyeglasses are highly convex on the front surface or less than 43mm across, it might not matter because the eye lens is huge at 43mm across.

As an aside, only my 40mm Meade 5000 Plossl has an eye lens that large (also 43mm).  It has 29mm of usable eye relief.  If it didn't degrade with astigmatism in the outer 25%, it would be a winner for eye glass wearers.  It is useful for outreach with the eyecup raised a bit.

If we're talking non-commercial, I have a Rini prototype 42mm Erfle with a 52mm diameter eye lens and 23mm of usable eye relief with a 68 degree AFOV.

[Louis D]

On 9/24/2017 at 14:48, 25585 said:

I had pondered about this ep before plumping for the Nikon 17.5

Once you've got the Nikon in your posession, could you try measuring the eye relief directly by shining a light into the field lens end then moving the eyepiece back and forth relative to a flat surface in front of the eye lens until the circle is at its smallest?  The distance from the top of the housing (eye cup screwed down) to the flat surface is the usable eye relief.  Thanks!