Available/Usable eye relief in Hyperions

[DarkStar (Paul)]

Hi, I'm a newbie and I have just bought a Nexstar 8SE.

The next important step is to buy some decent eyepieces for it.
I have severe astigmatism (4.5) and so I really need to keep my glasses on, and probably even for the smaller exit pupils.

I have measured the usable eye relief of the 25mm plossl that came with the scope by focusing a light through the eyepiece from a few meters away and measuring the distance from the eyeguard to the focal point.
This showed about 14mm of usable eye relief (adding this to the 5mm or so that the eye lens is recessed gives a total eye relief approaching the 20mm stated for that eyepiece).
14mm is not enough for me to see the entire (50 deg) FOV and I still have to press my eyeglasses closer to my eye, which twists them and causes some distortion to the image.
I reckon I need more like 16mm of usable eye relief.

From reading the forums, it appears that the Baader Hyperions in 21mm, 13mm and 8mm focal lengths are very popular with owners of 8" f/10 SCT's.
They are supposed to have 20mm of eye relief, and the eyeguard looks like it is only 2-3mm high, so that should give 17-18mm of usable eye relief.

However, I have found a couple of posts where people say that the eye relief varies across the focal lengths of the Hyperions and the usable eye relief could be as short as 11mm on some.

Before I buy the wrong eyepiece(s), are there any owners of Hyperions out there who would be willing to measure the usable eye relief using the method above?
Also, with the new 10mm focal length - is this a better choice than the 8mm for planetary observing? (I think 9mm is probably best, but they don't do that one)

If the usable eye relief turns out to be too short for me, is there another eyepiece in the same price bracket that has plenty usable eye relief and will perform as well as the Hyperions?

Paul.

[GeoffW1 (Geoff)]

Hi,

In a Hyperion 17mm that is about 20mm from the glass, or about 5mm above the (not rolled down) rubber eyecup, which is 15mm length. When rolled down the eyecup edge is about 4mm above the glass.

In a 8mm Hyperion it is clearly less, about 15mm from the glass, or about level with the eyecup.

In a borrowed Televue Ethos I have for a bit, it is also about 15mm from the glass.

http://www.iceinspace.com.au/42-286-0-0-1-0.html

http://www.ozscopes.com.au/william-o...eyepieces.html

These WO EPs are specified to be 20mm eye relief. Maybe someone can give you a report?

Cheers

[DarkStar (Paul)]

Thanks Geoff.
Looks like the Hyperion 8mm is off the table, but the 17mm should be OK.

The WO LERs look good, but only the 12.5 would be suitable for my scope (the 6 might be a little too short). I would need to confirm the eye relief on that one also, given the lack of accuracy in the Hyperion figures.

What a pity the usable eye relief figures aren't readily available.

[rmcconachy]

I've no hands on experience with the William Optics LER ocular line but I will note that the same (OK, very similar looking and reputedly the same) eyepieces are also offered at substantially lower prices under other names, e.g., Astro-Tech LER and Zhummel Z Series Planetary.

[DarkStar (Paul)]

Thanks for the advice Richard.

I have found a us website www.astronomics.com that quotes the measured eye relief for the eyepieces they sell, and the astro-tech is in there with 20mm of eye relief.

I will search foe reviews of the astro-tech and zhumell to see how they do.

Astronomics also show ultima lx and x-cel lx with 16mm eye relief and the Meade hd-60 with 17mm of eye relief. How do these compare with the astro-tech?