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Wearing Glasses and Eye Relief

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#1 Bill McNeal

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Posted 22 August 2013 - 11:57 PM

I wear glasses for nearsightedness (no astigmatism). What's the minimum eye relief I should look for when buying an EP?

Or will the EP focus for me without having to wear glasses at all? Are there some brands that are really good/bad at this?

#2 GlennLeDrew


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Posted 23 August 2013 - 12:38 AM

Eyeglasses reduce eye relief, and so can cause a loss of field of view due to the iris being forced too far back. Severe near- and far-sightedness can impact ability to focus if the focuser range is already limited or near the end of travel, this being more potentially problematic for larger exit pupils (the departure from 'true' focus scales linearly with eyepiece focal length.)

#3 cjc



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Posted 23 August 2013 - 03:13 AM

People say 17mm or so, but I think you need to try some out, because eyes are different and the eyepiece manufacturer's specification gives the optical rather than the usable eye relief.

If your correction is predominately for short sight (so the spectacle lens is concave) then the lens acts as a mild barlow extending the focal point, conversely it is shortened for long sight. Other factors include how close fitting your spectacles are, the dilated size of your eye pupil and how tolerant you are of vignetting. I am told that I am an outlier but I have found I can use these:

Antares ortho 12mm, with 9mm marginal
Baader Hyperion 17mm, Aspheric 36mm
ES68 24mm, 16mm (marginal)
ES82 11mm, 8.8mm (marginal), 6.7mm (vignetted) 4.7mm (severely vignetted - only for focusing for others)
Pentax XF 8.5mm
SWA 38mm
TMB planetary series
Vixen NLV series
Vixen NPL 20mm, 30mm

#4 Lamb0



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Posted 23 August 2013 - 04:32 AM

:FarmerRon: I kinda thought 20mm was a pretty good rule of thumb for eyeglass wearers. :shrug:

#5 seawolfe



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Posted 23 August 2013 - 04:43 AM

I too wear eyeglasses for nearsightedness and have tri-focals to boot. But I find that with my long eye relief EP's, I can either use them without my glasses and have the eyecups up, or roll the eyecups down and use my glasses. Either way it works fine.

Just gotta remember that if I remove my glasses and set them down, where I put them.... grope, grope... :confused:

#6 Hermie


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Posted 23 August 2013 - 05:04 AM


If you don't have astigmatism you don't need to wear your glasses at the eyepiece. The only disadvantage is if you are sharing the views with someone else, they will have to re-focus.

Since you are near-sighted, I expect you will be able to read your charts OK. But you will probably need to put your glasses on to see the sky, which can be annoying depending on your finder type.

I like to wear my glasses with the lens close to my eye, so I can get by with as little as about 13mm eye relief. You won't know what works for you until you try for yourself. As Lamb0 says, the rule of thumb is 20mm.

If you are going to wear glasses at the eyepiece, you need to check the eye relief before you buy new eyepieces. Some eyepiece lines with good eye relief are the Delos and Radian, Pentax XW and XL, Vixen LVW, Baader Hyperions. Most longer focal lengths are fine as well.

Short ER eyepieces are any short focal length simple EP, like Ploessls and Brandons. You may also lose some field of view with some Naglers and Ethos.

The weakest link in the optical chain is my dang eyes!


#7 cjc



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Posted 23 August 2013 - 05:14 AM

Just gotta remember that if I remove my glasses and set them down, where I put them.... grope, grope... :confused:

I have my viewing glasses on a loop so they do not get lost.

#8 SeattleScott


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Posted 23 August 2013 - 05:39 AM

16mm or more works for me. 17 works for most people. 20 is considered ideal.

#9 SteveG


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Posted 23 August 2013 - 12:22 PM

I would leave your glasses off at the eyepiece.

#10 Luigi


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Posted 23 August 2013 - 01:38 PM

One thing about observing without wearing corrective lenses, it utilizes the eyepiece at a different focal distance than it was optimized for. For example: If you are nearsighted and focus with distance glasses on, you focus with the eyepiece racked to the same point a person with normal vision would have it. This puts the eyepiece at the its design (optimum) distance from the objective's focal plane. Remove your glasses, and you have to rack the eyepiece inward to to focus. This places the eyepiece closer to the focal plane of the objective, closer than it was designed for. This will have some small (perhaps negligible) effect on its performance.

#11 Kent10



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Posted 23 August 2013 - 02:01 PM


That is very interesting. I am very near sighted at -13 and just this morning I was observing the sun with my Mark V bino and Delos and Pentax XW pairs. I used 20mm, 17.3, and 14mm pairs. I tried with and without my glasses. The magnification was so different with and without my glasses that it was like having a set of eyepieces in between each of these. I didn't look critically though to see if there were differences.


#12 Starman1


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Posted 23 August 2013 - 02:49 PM

The "effective" eye relief of most eyepieces, which is the actual distance the exit pupil is from the top of the eyepiece, is always less than the manufacturer states for the eye relief because the manufacturer's spec is from the glass out.

If I want to wear my glasses at the eyepiece, even with thin glasses close to my eye, I find 20mm (mfr's spec) to be about the minimum I will tolerate (translates to a real eye relief of ~17mm).
I don't want to press my glasses against the eyepiece for one (they cost more than the eyepiece) and I don't want to jam them so close to my eye I get eyelash oils on the inside of my glasses.
Fortunately, I have little or no astigmatism, so I can view without glasses (and tolerate eye reliefs as short as 10mm).

I suspect that if you took two eyepieces with identical eye reliefs, the wider apparent field would be the one harder to use with glasses and still view the whole field. So far, no manufacturer has designed an 82-120 degree apparent field eyepiece series usable by most glasses wearers (except, perhaps, long focal lengths).

But if you don't have a lot of astigmatism (say, over 0.5 diopter), there is no particular reason to observe with glasses on. As for the inconvenience of hanging them around your neck on a lanyard? I can't read my charts or DSC without putting them on, yet I observe without them. So they go on and off my face 500 times in a night. I tried observing WITH glasses on, but didn't like the image quality. TeleVue they ain't. :lol:

#13 iluxo


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Posted 23 August 2013 - 03:09 PM

I observe with mine on. Yes you can observe perfectly well without them but the problem is more the inconvenience of taking them on and off to use digital setting circles, the telescope contoller, atlases, charts iPhones or tablets, etc.

Better to leave them on. My eyepieces have 20mm or more eye relief.

Make sure your eyepieces all have a soft rubber ring of some sort at the business end, or your specs will be quickly scratched and ruined.

#14 GeneT


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Posted 23 August 2013 - 09:59 PM

Eye piece manufacturers often misstate eye relief and the lens design also plays on this issue. I have found that Naglers with 17mm or more of eye relief allows me to view with my glasses on. Nineteen or 20mm such as had by the Delos and Pentax XW's is even better. The type of eye glasses also plays on this issue. I wear thin polys that ride high up on the bridge of my nose. That puts my glasses close to the eye piece. I recently bought some Ethos eyepieces. They have 15mm of eye relief. I have no astigmatism, and affixed a chord around a spare set of eye glasses. That allows me to put them on when looking through the Telrad, or star charts, then removing them when going to the eye piece. Since you don't have astigmatism, you should be able to view fine without glasses.

#15 urassner


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Posted 24 August 2013 - 08:16 AM

I usually have my glasses on during observing and found the Pentax XW with 20 mm eyerelief very comfortable. I sold my Ethoi (3.7 mm & 6 mm) because I found them not as comfortable and certainly could not use them with my glasses on, even though they have a nominal eyerelief of 15 mm. The lens is somewhat recessed. However, I can use my 16 mm Brandon (volcano top) with my glasses on, even though the eyerelief should be around 13 mm.

#16 SkyRanger


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Posted 24 August 2013 - 09:22 AM

When I take my glasses off the sky becomes a big furry blob. This destroys the feeling of connection to the sky I have when observing. So, for me, glasses stay on every waking moment.
Pentax XWs and Deloi and Nagler T4s have become my best friends, as well as longer FL Plossls and Powermates.
About the least eyerelief I can tolerate is 17mm.
I would love to try an Ethos, but 15mm is just not enough eyerelief for me.

Gordon G

#17 Dan McConaughy

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Posted 24 August 2013 - 06:11 PM

I use Dioptrix on my 41mm Panopic and 31mm Nagler, based on the Televue website's suggestions. It's hard to share an eyepiece with a dioptrix, though; so on some objects, if I'm observing with someone else, I wear my glasses. Mostly I use a 21mm Ethos or shorter f.l. eyepieces and avoid the need to wear glasses.

#18 Scott Watson

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Posted 24 August 2013 - 08:36 PM

16mm or more works for me. 17 works for most people. 20 is considered ideal.


#19 psyhiker


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Posted 24 August 2013 - 10:36 PM

View without your glasses on, put them up on your head...that's what I do, never lose the glasses, eye relief not an issue

#20 izar187



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Posted 25 August 2013 - 01:06 PM

Yes to 20mm eye relief eyepieces. They're the bees' knees. For sharing the view too.
Yes to full time 20/20 vision when out at the telescope.
For thru the ep, the finder, looking up at the sky and around the observing site.

Yes to glasses up on top of the head, rather than dangling.
Can be strapped lightly in place there too if necessary, if their frames are up to this.
Also yes to a dedicated pocket for the glasses, rather than setting them down nearby.
The pocket will defog them too, which can happen in summer humidity and winter cold.

Yes to observing with glasses off. I did for decades.
And still can whenever I want.

Did I mention Yes to 20mm eye relief eyepieces?

#21 GeneT


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Posted 25 August 2013 - 04:03 PM

I would love to try an Ethos, but 15mm is just not enough eyerelief for me.

For years I thought the same. I tried first a 13mm Ethos. I found that 15mm was a nice amount of eye relief without wearing glasses. I got a strap that I put around a spare set of glasses. It is easy to put them on when viewing through a Telrad, looking at the sky, or reading maps. Then, I take them off when at the eyepiece.

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