Nov

27

Eye Relief and Why it Matters

Filed Under Accessories, Telescopes 

When buying a telescope eyepiece or binoculars, an important consideration is eye relief, which is the distance between the exit pupil of the optical system and the entrance pupil of the eye; in other words, how much space there is between last element (the farthest back piece) of the the eyepiece or binoculars and the place where your eye goes to clearly see the image.

The greater the eye relief, generally, the more comfortable the binocular or telescope eyepiece usage will be, since your eye will not be pressed right up against the last piece of glass. Also, the greater the eye relief, the easier it is for people who wear glasses to use the eyepiece or binoculars, as the extra eye relief accommodates the space that glasses take up.

Ideally, you want what is known as the exit pupil of the eyepiece or binoculars and the entrance pupil of the eye to be the same size so that you are able to see a bright and crisp image. However, to have a large amount of eye relief, the exit pupil of the eyepiece or binoculars must be larger than the entrance pupil of the eye so that you have space to move back from the rear optical element; the result is that you are wasting some of the light that your telescope eyepiece or binoculars are gathering, but you are gaining a more comfortable viewing experience.

This post was written to answer a reader’s question, if you would like to have your questions answered, email questions@telescopes.org or comment on the site.

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Comments

2 Responses to “Eye Relief and Why it Matters”

  1. lancer on December 7th, 2008 7:54 pm

    This article is useless. I don’t want a long, drawn-out technical explanation of all this telescope jargon. I don’t even need to know it. All I want to know is what the most effective, least expensive telescope I can get, that will let me see Saturn’s rings, the Great Red Spot on Jupiter, and a fairly good amount of detail on the moon. This article might make some astronomer-type feel good about themselves, but it is worthless for the casual observer. In fact, one might be able to make a case to say it was written to keep the casual newbie away from astronomy.

  2. admin on December 7th, 2008 8:02 pm

    Thank you for writing, this article should be of use to you, http://www.telescopes.org/telescopes/a-good-affordable-telescope-orion-skyquest-xt8/.

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