Eye relief. Whats it all about?????

[M4lcs67]

Having been a non spectacle wearer for my whole life, I am looking at having to start wearing them after my recent eye operation.

My question is about eye relief. What is it and why do people make reference to it when taking about eyepieces etc?

Is it the distance from the front of your glasses lens to the eyepiece lens??? Surely you could adjust that by moving your head further/closer to the eyepiece and using the focusing knob on the scope accordingly? Or maybe I am barking up the wrong tree?

[The Sailor]

Here, give this a read, may go someway to explain.

http://en.wikipedia.org/wiki/Eye_relief

Jim

[andrew s]

Eye reilef is how far the exit pupil of the eyepeice from the end of the eyepeice. You need to put the pupil of your eye at the eyepeice exit pupil to ensure you get the fully illuminated field into your eye ball.

If the eye relief is too low you can do this comfortably or not at all with glasses. However, if you are just short or long sighted you can remove your glasses and just refocus the telescope to compensate. I used on old pair of specs with one lens removed to look through the scope and look at charts or the sky direct with the eye that still had the corrective lens.

Regards Andrew

[M4lcs67]

Thanks alot Jim.

[michael.h.f.wilkinson]

Rule of thumb from a long-time wearer of glasses: anything below 16-17mm is a hassle. I avoid the ethos range for this reason (15mm). I had a Meade Series 5000 14mm UWA with 14-15mm eye relief. It was very nice and sharp but annoyed me after a while, because my glasses kept bumping in to the EP, causing the image do bounce around annoyingly. I now have a 12mm T4 Nagler, which has 17mm eye relief, which makes all the difference.

[RikM]

I wear glasses to observe and also find eyepieces with eye relief in the 16 - 20 mm range much more comfortable. I can just get away with a 15mm Plossl but I think that is mainly due to it showing a smaller field anyway.

[John]

You can have too much eye relief. There are a few longer focal length eyepieces that have so much eye relief that you have to "hover" your eye well clear of the top of the eyepiece to find the right viewing point. Too close or too far and you get black outs, kidney beaning and / or loss of field of view which is frustrating and can place strain on the observer to remain still. The more thoughtfully designed eyepieces have adjustable top sections so that you can move the top of the eyepiece (not the top lens though) to just the right position for you. You can then be confident, if your eyebrow or glasses frame is touching the rim of the eyepiece, that you will be at the right viewing point right away.

[M4lcs67]

Thanks guys. Really helpful info from you all.

[michael.h.f.wilkinson]

You can have too much eye relief. There are a few longer focal length eyepieces that have so much eye relief that you have to "hover" your eye well clear of the top of the eyepiece to find the right viewing point. Too close or too far and you get black outs, kidney beaning and / or loss of field of view which is frustrating and can place strain on the observer to remain still. The more thoughtfully designed eyepieces have adjustable top sections so that you can move the top of the eyepiece (not the top lens though) to just the right position for you. You can then be confident, if your eyebrow or glasses frame is touching the rim of the eyepiece, that you will be at the right viewing point right away.

Too true! I had problems with my old Vixen 36mm Plossl, which had about 32mm eye relief, and was quite tricky to use, especially for novices. The 40mm TMB Paragon which replaced it had 20mm, which is just right. My current 31T5 Nagler has 19, which is fine.

[bingevader]

How will the operation affect your vision?

I'm short sighted, so I tend to look at all distant objects through a lens.

As I don't need my glasses to read reference manuals I tend to leave them off altogether when using a telescope.

Someone once suggested contact lenses as an alternative, but I couldn't get the hang of them!

Cheers

[M4lcs67]

Hey bingevader.

Had the op to remove a large floater from left eye at the beginning of August. (The actual term for the proceedure is a vitrectomy). Also to replace the lens in that eye with a false one at the same time. The op was a difficult one as the gel in my eyeball was quite difficult to remove, so the surgeon had to do some laser surgery on my retina as some tiny tears were caused to it. Then she had to put sillicone oil into my eyeball to aid the healing process. Has the oil removed a month later as my retina has healed well. Just continuing with the healing at the mo and I go back to see the surgeon on Thursday. When I had the original operation she said that she took my original prescription and replaced my own lens with a false one of the same size. When I saw her a month ago she did say that it looked that the lens had shifted slightly. As things stand everything is totally blurred. Close up or far away (Apart from the floater the vision in that eye before the op was pin sharp). This is why I think I will need glasses from now on.

I did know before I had the op that I may end up having to wear glasses and I don't regret having it done as the whole point of it was for me and my astronomy. The floater became such a problem and was ruining my enjoyment of it. Once I have got some glasses and can see sharply again I will be able to resume things with my scope and will be able to use my new C9.25 for only the 2nd time. Huzzah!!!

[michael.h.f.wilkinson]

Best of luck with the healing process.

[Jiggy 67]

One question and I don't mean to sound ignorant. I am new to wearing glasses and I only wear them for reading at the moment, I've never worn them for observing, but I do think they are deteriating....my question is, why would a spectacles wearer need to wear glasses whilst observing?? doesn't the eyepeice provide all the magnification required??

[Naemeth]

One question and I don't mean to sound ignorant. I am new to wearing glasses and I only wear them for reading at the moment, I've never worn them for observing, but I do think they are deteriating....my question is, why would a spectacles wearer need to wear glasses whilst observing?? doesn't the eyepeice provide all the magnification required??

If you have astigmatism it will need to be corrected by either your glasses or another astigmatism corrector (Dioptrx by TeleVue does this). But you are right, short and long sight are corrected for by the telescope, or more specifically, the focuser.

[M4lcs67]

Yeah I must say I thought that myself. You can use the scope to adjust your view by turning the focuser. Although what to do when you are not at the eyepiece? Changing things over, changing settings on the scope/mount etc.

[Dunkster]

Welcome back Malc, glad to hear you're doing we'll

I wear glasses for distance but tend not to use them after alignment as it doesn't feel right... I suffer with slight astigmatism in one eye, but besides that I just abuse the focus travel of the scope. The great thing with the focal ratio of SCTs is that the astigmatism doesn't appear to affect the view with the EPs I have. Depending on what you need the glasses to correct, you may or may not get away with the same.

From memory the Hyperii have generous eye relief so you should be ok either way

[Dunkster]

Yeah I must say I thought that myself. You can use the scope to adjust your view by turning the focuser. Although what to do when you are not at the eyepiece? Changing things over, changing settings on the scope/mount etc.

Probably a non-starter at the moment given you've just had surgery and all, but it maybe worth checking if it's a possibility longer term... contact lenses. Personally I've never been keen on the idea, but my correction is relatively small.

[adamw]

Sorry to hijack this post but on the subject of eye relief. I have a 5mm baader ortho which I seem to struggle with. Is there a knack to looking through these ? I don't where glasses but my eyelashes catch the eyepiece and it is very uncomfortable.

[Moonshane]

my only advise when using such short eye relief eyepieces is blink a little away from the eyepiece. personally I find the 7mm BGO at the limit of comfort. I use a nagler zoom for the 6-3mm range.

[michael.h.f.wilkinson]

Sorry to hijack this post but on the subject of eye relief. I have a 5mm baader ortho which I seem to struggle with. Is there a knack to looking through these ? I don't where glasses but my eyelashes catch the eyepiece and it is very uncomfortable.

My experience with a 5mm ortho (Circle-T) suggested to me that the only way to deal with them was to get a different eyepiece . Even other users without my astigmatism found it a pain.

We hatessss sssshort eye relief, yessss we doessss my precioussss!

[bingevader]

Hey bingevader.

Had the op to remove a large floater from left eye at the beginning of August. (The actual term for the proceedure is a vitrectomy). Also to replace the lens in that eye with a false one at the same time. The op was a difficult one as the gel in my eyeball was quite difficult to remove, so the surgeon had to do some laser surgery on my retina as some tiny tears were caused to it. Then she had to put sillicone oil into my eyeball to aid the healing process. Has the oil removed a month later as my retina has healed well. Just continuing with the healing at the mo and I go back to see the surgeon on Thursday. When I had the original operation she said that she took my original prescription and replaced my own lens with a false one of the same size. When I saw her a month ago she did say that it looked that the lens had shifted slightly. As things stand everything is totally blurred. Close up or far away (Apart from the floater the vision in that eye before the op was pin sharp). This is why I think I will need glasses from now on.

I did know before I had the op that I may end up having to wear glasses and I don't regret having it done as the whole point of it was for me and my astronomy. The floater became such a problem and was ruining my enjoyment of it. Once I have got some glasses and can see sharply again I will be able to resume things with my scope and will be able to use my new C9.25 for only the 2nd time. Huzzah!!!

My goodness, here's to a speedy recovery!

I'm assuming the other eye is no better?

Would contact lenses be an option?

Best of luck, I hope it all works out okay for you.

Cheers

[LukeSkywatcher]

I now wear glasses 24/7 for reading,tv and driving. However i do not wear them while observing. My favourite EP's are the Vixen NPL and they apparently dont have good eye relief but i dont notice it.

I love them.

[andyboy1970]

I have tried lots of expensive eyepices (Ethos, X-cel, etc) and have found them not suitable to my eyes (glasses for reading only).

I'm the same as Paul and use Vixen NPL's 30mm, 20mm & 10mm and find them perfect for me.

If I bought anything less than the 10mm I would get Vixen NLV's.

[LukeSkywatcher]

I have tried lots of expensive eyepices (Ethos, X-cel, etc) and have found them not suitable to my eyes (glasses for reading only).

I'm the same as Paul and use Vixen NPL's 30mm, 20mm & 10mm and find them perfect for me.

If I bought anything less than the 10mm I would get Vixen NLV's.

I have a 25MM Vixen NLV and do not think it is as good as the NPL's (8,15,30mm) i have.

[andyboy1970]

I have a 25MM Vixen NLV and do not think it is as good as the NPL's (8,15,30mm) i have.

Interesting, I find the 10mm comfortable (not as comfortable as the 20 & 30 I use) so thought NLV's which are all 20mm eye relief would be better below the 10mm npl.