Ethos21, How much eye relief?

[alanjgreen]

Televue state that the Ethos21 has 15mm of eye relief and 100 degree actual field of view in their published specification.

http://www.televue.com/engine/TV3b_page.asp?id=20&Tab=EP_ETH-21.0

Has anyone actually MEASURED the eye relief and can confirm that this is indeed what it has?

Can anyone confirm that the Ethos21 actually does show 100 degrees FOV or is it actually less?

Thanks in advance,

Alan

[John]

I have not actually measured the ER or the AFoV but, having used quite a lot of 100 and 110 degree eyepieces of various brands I'm pretty confident that the E21 delivers it's full AFoV and in terms of ER I (as a non-glasses wearer) can see the full extent of the AFoV with my eye socket resting gently on the rubber eyecup edge. I don't need to tilt my head although my eye might be, unconsciously, moving around of course - I'd have to find a way to film it from inside the eyepiece to determine that I guess

Like most ultra wide field designs the Ethos 21 has a concave eyelens and ER is measured from the top surface of the lens so there will be a couple of mm of useable eye relief "lost" due to that. The eye lens is recessed around 1mm below the physical top of the eyepiece so I'd estimate that the useable eye relief is around 12mm of the stated 15mm.

Sorry that these are subjective rather than measured figures but they are based on my experiences and comparisons with quite a few eyepieces FWIW.

I had the ES 20 / 100 before the E21 and with that I needed to roll the rubber eyecup down to see the full AFoV. I don't need to do that with the E21.

It's a much discussed issue on forums so probably somebody somewhere has actually measured the true figures. I'd be surprised if they were too far from my estimates though.

Also worth remembering that the useability of eye relief depends on other factors as well, no least the contours of the observers face and their preferences too

Of the 4 Ethos eyepieces that I currently own, I'd say that the 6mm has slightly tighter eye relief. The 21, 13 and 8mm seem pretty consistent.

 

[martinl]

I’d agree with John, the 15mm ER of the 21mm Ethos is probably as accurate as any ER spec is likely to be. My 10mm might have a fraction of a mm more, the 6mm perhaps a mm less (both nominally 15mm). 

The Panoptic 24mm (also nominally 15mm ER) feels like it has noticeably less ER than the 21mm Ethos, but this could be because you have AFOV to spare with the Ethos. I don’t like using the Pan with glasses but the Ethos is marginally ok. 

I’m not really an Ethos person, but the reason I hang on to the 21mm is because it is such an effective eyepiece. It works as a 36mm field stop finder EP (with some discomfort, forcing me to move my head around a bit) and also as a 21mm, medium-low magnification, EP with 80-90 degree of useable AFOV at eyeglass-friendly viewing distances. 

[Stu]

21 minutes ago, John said:

I'd estimate that the useable eye relief is around 12mm of the stated 15mm.

That's within a mm or so of @Louis D's estimate John so I'm sure it is in the right ball park.

I can't find any actual measurements out there, but did find this quote which seems to sum it up:

'I don't doubt the Ethos' stated eye relief, but what you're describing is really ergonomics.  The triangle formed looking at the observer in profile by the opposite sides of the Ethos' field stop and the observer's pupil 15mm from the eye lens is a very large angle at the vertex.  The geometry of the Delos provides a much sharper angle.  The two eyepieces feel very different.  I have both Ethoses and Deloses.  I am leaning the other way - dumping the Deloses for Ethoes - as I find that I prefer the squatter ergonomics and immersion of the Ethos over the tighter peeking-in feel of the Delos, though neither are bad eyepieces by any stretch.'

There should perhaps be another definitions which is 'Useable eyerelief' measured from a line across the top of the eyeguard at its shortest. Any reduction from the standard eye relief will be to do with the curvature of the exit lens and the ergonomics of the eyeguard.

It helps if you look like this I guess...

[martinl]

8 minutes ago, Stu said:

There should perhaps be another definitions which is 'Useable eyerelief' measured from a line across the top of the eyeguard at its shortest.

Amen to this. 

I agree about ergonomics being a key factor. The E21 is a large EP and can easily interfere with your ability to move your head around. I find there are some parts of the field stop I can’t easily see because my nose or eye socket gets in the way. I guess I could consider surgery, but for now I think I’ll just live with it :-)

[Paul73]

In order to get the full fov in the 21mm Ethos, I almost need to climb inside and look around! The concave lense seems to make it comfortable to use and totally immersive. 15mm sounds about right for naked viewing. I couldn’t use it effectively with glasses. 

Paul

[alanjgreen]

2 minutes ago, Paul73 said:

"naked viewing"

Its too cold in Cumbria for any of that!

[Paul73]

The view is so good that you don’t notice the cold........

[25585]

How critical is eye positioning for the 21? More as a cut-off/kidney bean issue than seeing the whole FOV?

 

[martinl]

5 minutes ago, 25585 said:

How critical is eye positioning for the 21? More as a cut-off/kidney bean issue than seeing the whole FOV?

 

Not very. I haven’t had any problems with eye positioning. It may not be quite as forgiving and comfortable as the 22mm LVW, but few EPs are.

[John]

I've found all the Ethos eyepieces quite straightforward to view through. I graduated to them from Naglers (some of which are quite fussy on eye placement) and found the Ethos experience to be more comfortable overall.

 

[Don Pensack]

On 1/25/2018 at 01:06, alanjgreen said:

Televue state that the Ethos21 has 15mm of eye relief and 100 degree actual field of view in their published specification.

http://www.televue.com/engine/TV3b_page.asp?id=20&Tab=EP_ETH-21.0

Has anyone actually MEASURED the eye relief and can confirm that this is indeed what it has?

Can anyone confirm that the Ethos21 actually does show 100 degrees FOV or is it actually less?

Thanks in advance,

Alan

It has 15mm of eye relief from the glass.  But the top lens is concave, and the rubber eyecup, even folded down, is a bit above the aluminum, so you lose about

3mm in effective eye relief in the field.  There is no way these are compatible with glasses.  However, the eye relief is quite comfortable without glasses.

[Pig]

Pretty much the same from me as the other comments... very easy to view through and I haven’t even thought of kidney beaning since using them.