# Binocular eyepieces

**URL:** <https://boards.straightdope.com/t/binocular-eyepieces/4375>\
**Category:** Factual Questions\
**Created:** [October 31, 1999, 10:16pm UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375 "1999-10-31T22:16:00Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![toecutter](https://avatars.discourse-cdn.com/v4/letter/t/df705f/32.png) [@toecutter](https://boards.straightdope.com/u/toecutter)\
**Post date:** [October 31, 1999, 10:16pm UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/1 "1999-10-31T22:16:00Z")

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On most binoculars, only one eyepiece has markings and only one is adjustable. Its always the right (in my experience). How do you adjust for the left or is it true that only right eyes are weaker. I’ve tried twisting and turing (toward the+ and - signs)but can detect very little difference in vision. What gives?

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**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\
**Post date:** [October 31, 1999, 10:45pm UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/2 "1999-10-31T22:45:00Z")

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Adjust the larger focus knob until the left eye is clear, then turn the knob on the right eyepiece until the right eye is clear. Of course, this has only a limited effect. If your eyes a very different, it won’t do any good. Then you can do as I do; look through only the strongest eye. 🙂  
Peace,  
mangeorge

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Work like you don’t need the money…  
Love like you’ve never been hurt…  
Dance like nobody’s watching! …(Paraphrased)

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**Author:** ![toecutter](https://avatars.discourse-cdn.com/v4/letter/t/df705f/32.png) [@toecutter](https://boards.straightdope.com/u/toecutter)\
**Post date:** [October 31, 1999, 11:13pm UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/3 "1999-10-31T23:13:00Z")

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Thank you very much mangeorge.  
So obvious when you know how. _Blush_.

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**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\
**Post date:** [November 1, 1999, 3:51am UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/4 "1999-11-01T03:51:00Z")

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Aw shucks, twern’t nuthin, friend. 🙂  
Peace,  
mangeorge

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**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\
**Post date:** [November 1, 1999, 3:04pm UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/5 "1999-11-01T15:04:00Z")

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Actually, on a good pair of binoculars, the right eye adjustment is the equivalent of at least half the focal length adjustment made by the central knob, so really it should resolve all but the really really bad vision. To see this in action, measure the distance the eyepiece travels for each knob…

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**Author:** ![Chef\_Troy](https://avatars.discourse-cdn.com/v4/letter/c/85f322/32.png) [@Chef\_Troy](https://boards.straightdope.com/u/Chef_Troy)\
**Post date:** [November 1, 1999, 3:37pm UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/6 "1999-11-01T15:37:00Z")

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Also, there are diopter eyepieces for significantly disparate eye strengths.

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Live a Lush Life  
Da Chef

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**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\
**Post date:** [November 2, 1999, 6:46am UTC](https://boards.straightdope.com/t/binocular-eyepieces/4375/7 "1999-11-02T06:46:00Z")

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- 
  - 
    - And there do exist astronomical binoculars which have both eyepieces separately adjustable; in some models that’s the only focusing method supplied.(expen$ive) - MC