i don't understand eye relief..

[Scott]

can anyone explain to me what eye relief means/does? i wear glasses but not when using the telescope. does this make any difference or not? sorry for what is probably a very basic question but i'm a very basic person. lol

[Stephen]

Eye relief as I understand it is how close to the piece of glass your eyeball has to be to see through it properly.

As a glasses wearer, anything with less than 16mm of ER is virtually impossible for me to use, as I can't get my eyeball close enough to the glass.

16mm is useable, 20mm is perfect.

If you don't wear glasses at the scope, it's just a matter of personal comfort. Even with no glasses, some EPs can have 4mm of ER which means pushing your face right up to the EP!

[Ags]

It depends what your glasses are for and what sort of magnification you are using.

If you have simple short/long sight, you can correct for this by focussing the telescope so you do not need to wear your glasses.

If you have astigmatism, you need the glasses to correct for this at low powers. At high magnification, the light beam you are viewing is very narrow, so you do not need to wear glasses even if you have astigmatism. The exact point at which magnification cancels out astigmatism depends on how bad the astigmatism is, I don't have any figures for that. It also depends on the size of the telescope - I _guess_ that powers of aperture in mm x 1.5 would cancel out most astigmatism.

If you need to or want to wear glasses while observing, then you need to get EPs with long eye relief. These EPs bring the light together at a point further from the eye lens, so your eyeball does not have to be so close to the glass. Basic EPs like plossls have very short eye relief at short focal lengths (say 8mm), so many find these uncomfortable to use even without glasses.

I enjoy long eye relief EPs for the comfort, even though I can observe without glasses. But I have long eye relief binoculars so that I can observe while wearing glasses - it is frustrating trying to find stuff with glasses, then taking the glasses off to use the bins, so long eye relief is a real benefit... :-)

[Carbon Brush]

Simple non technical answer.

This is the distance from the front of the eyepiece to your eyeball.

So, if you have an EP with short eye relief, using with specs is a problem. The EP to eye distance is determined by your specs. If this exceeds the EP eye relief, a problem.

But remove your specs and refocus and this is generally OK. If you don't have astigmatism. Sorry starting to get technical.

A long eye relief EP without specs can mean you having to hold your head steady in mid air some distance from the EP. But Usually the EPs have a big rubber eyecup and maybe a twist/fold facility to set the distance. A light touch to the eyecup helps keep your head steady.

The eyecup also helps block stray light.

Hope this helps.

[Scott]

thanks so much for the quick responces. its so straight forward when someone explains it. the eps that came with my 200p must be quite short because my eye is almost touching the eyepiece when i use it

ps. also they have no eyecaps with them. can you buy them seperatley?

yes they have. i just didn't see them. sorry

[brantuk]

The eyepieces supplied will have fold up rubber eyeguards - did you extend them?

[scuffer]

learning something every day .... I didn't fold up my rubber eyeguards