What is the 'eye relief' of which you speak?

[neptune1]

Just that really, interpretation most welcome, thank you

[Astro Imp]

It refers to the distance from the eye piece to the image produced which is where you need to place your eye to view. Very short eye relief is not easy to view and those of us who use glasses need longer eye relief as we can't get our eyes really close.

[ScottS]

Its how close your eye needs to be to the eyepiece to see the whole field of view.

[neptune1]

Ah I see. How would you know if an EP has good eye relief, what things should one look for? Thanks!

[ScottS]

Generally higher magnification EP's have less eye relief.

[Owmuchonomy]

Generally higher magnification EP's have less eye relief.

Yes, so for example M42 through my 8mm EP, you get very close but feel as though you are 'falling' into the gas. With the 40 mm EP you relax away from the glass and can look around the sky at Orion's sword.

Sent from my iPhone using Tapatalk

[neptune1]

Great, thanks that makes sense.

[John]

Ah I see. How would you know if an EP has good eye relief, what things should one look for? Thanks!

The eye relief that an eyepiece has is usually quoted in the specifications of the eyepiece. The figure ranges from just a few mm for short focal length eyepieces of the orthoscopic and plossl design to 30mm or more for certain long focal length designs.

Whether an eyepiece has "good" eye relief can be a matter of personal taste. Some people are happy to get their eye snuggled in close to the top lens of the eyepiece whereas others prefer to be less intimate and, in the case of those that wear glasses when observing, can only get so close without their glasses bumping against the eyepiece top.

[neptune1]

The eye relief that an eyepiece has is usually quoted in the specifications of the eyepiece. The figure ranges from just a few mm for short focal length eyepieces of the orthoscopic and plossl design to 30mm or more for certain long focal length designs.

Whether an eyepiece has "good" eye relief can be a matter of personal taste. Some people are happy to get their eye snuggled in close to the top lens of the eyepiece whereas others prefer to be less intimate and, in the case of those that wear glasses when observing, can only get so close without their glasses bumping against the eyepiece top.

Thanks John, very helpful. 

[AlexB67]

If you wear glasses 15mm or greater is often recommended, though it can vary too depending on the eyecup design and how it is measured. The BST explorers I own only quote 13mm and I find them to have plenty with room to spare in practice. On the other hand I have  a maxvision that quotes a larger figure for the eye relief, yet it is on the limit for glasses. If you have 20mm eyerelief than usually whatever the eyepiece, you know you can be assured of very comfortable viewing with glasses.

It is worth bearing in mind when buying since eye pieces that have generous eyerelief is something you pay extra for usually , so if you feel you don't need it, but want good optical quality  without breaking the bank there are some very good eyepieces to be bought in the 50 - 100 pounds range, new or second hand if you are prepared to sacrifice on the eyerelief and a smaller field of view (FOV).

[neptune1]

If you wear glasses 15mm or greater is often recommended, though it can vary too depending on the eyecup design and how it is measured. The BST explorers I own only quote 13mm and I find them to have plenty with room to spare in practice. On the other hand I have  a maxvision that quotes a larger figure for the eye relief, yet it is on the limit for glasses. If you have 20mm eyerelief than usually whatever the eyepiece, you know you can be assured of very comfortable viewing with glasses.

It is worth bearing in mind when buying since eye pieces that have generous eyerelief is something you pay extra for usually , so if you feel you don't need it, but want good optical quality  without breaking the bank there are some very good eyepieces to be bought in the 50 - 100 pounds range, new or second hand if you are prepared to sacrifice on the eyerelief and a smaller field of view (FOV).

Thanks that's v. helpful. Which of yours are you glad you spent more/less money on? 

[AlexB67]

Thanks that's v. helpful. Which of yours are you glad you spent more/less money on? 

Nothing that I really regret, they were all bought at different stages. The 3 BST explorers were bought when I only had the 5 inch Dob and they were perfect at that time seeing I did not see much point spending lots on eyepieces for a scope that cost about 140 pounds new, and not knowing how far I would go with the hobby.

As I realised I would be in it for the long haul. I got a 10 inch Dob and gained more experience looking at targets and  the demands changed somewhat as my eyes became more finely attuned and more critical of some things.  The 10 inch DOb being that bit shorter focal ratio that bit more demanding on eye pieces also put demands on needing well optically corrected eyepieces.

I also found myself not using glasses for observing anymore as time went on, therefore the comfy eye relief of the BST were no longer that important to me, not for serious observing anyway, though I will put them on when scanning or searching the sky with the finder.  With that in mind the only thing I would probably change in the lineup now if I were to buy the BST lineup and the one 20mm Maxvision again and if my house got robbed tomorrow, would be to buy TV plossls instead for similar money.  I may still do so as when the do turn up since they cost a similar price second hand, and the shorter focal length ones are not much more than the costs of BSTs.  In the end it is no big loss, the  3 BSTs would just about buy me one premium eyepieces like a TV Delos new, and  cut in half at that

I still look to keep that  8/15/25mm or 3 eyepiece lineup for the smaller scope, but I feel perhaps they'll morph into 8/15/32 mm TV plossls over time.  but I have other things on the list  I want too, this hobby can be a sucker on the wallet

Suffice it to say, rightly or wrongly I convinced myself that a collection of Televue/pentax/vixen and some orthoscopics for the odd occasion is the way to go for my scope 10 inch Dob, and that that will be the best investment for me in the long run I feel.  But is a personal thing for each and everyone of us how much we want to spend on eyewear.

[ollypenrice]

One issue with long eye relief EPs is that you don't automatically have any physical feedback from the EP as to where to place your eye, so the better manufacturers build in an adjustable guide in the form of a cup which can be raised or lowered to your preference.

Olly

[neptune1]

Thanks very much. There is a 'bring and buy' sale at the local club in a few weeks so I am trying to get a little info and maybe a bargain on the night.

[michael.h.f.wilkinson]

I am very happy I have spent more on long eye relief EPs. 16mm is really the limit for me, although as has been stated, the quoted figures are merely a guide. Note that long focal length Plossl EPs (>30mm) tend to have too much eye relief. This means your eye needs to float uncomfortably far from the EP to get the image. I really hated this in the Vixen 36mm Plossl I used to have (otherwise a fine EP). To much relief is still better than too little