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Old November 7, 2017, 02:14 PM   #1
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Use a scope? Please read


I am researching scopes and thought this would be the best place for information I am seeking.

What are the common diameter sizes for eye pieces? Does the dimension pertain to inner diameter (glass) or outer diameter (housing)?

The amazon link from UTG shows multiple sizes but are these correct?

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Old November 7, 2017, 03:30 PM   #2
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When a scope specifications are 3-9x50, the 50 refers to the diameter of the glass (50mm in this instance).

You would need to go to the manufacturers website to see the specifications on the eye piece.

Here is an example for a Leupold scope. Look at the "Dimensions" tab for an outline drawing.
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Old November 7, 2017, 03:40 PM   #3
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The last number is the diameter of the objective lens, i.e., the lens at the front end of the scope. If the scope is variable power, the objective lens diameter will be the third number in the description of the scope specifications. Leupold's website seems to indicate the eye-piece diameter is the outside diameter of the scope at the eye-piece.
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Last edited by lefteye; November 7, 2017 at 03:59 PM.
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Old November 7, 2017, 04:26 PM   #4
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...which is kind of irrelevant. The ocular lens just puts the objective and focal image together for your eye. It’s size doesn’t matter as long as it creates a comfortable eye relief. There is a “right” size for the ocular lens and larger or smaller would make it worse. You rarely see any specs for them because they’ve generally gotten that part right.
It’s the objective lens that increases the scopes ability to gather light. The bigger the objective the brighter the scope in low light conditions and the less light you loose under extreme zoom.

The best way to experience this is with a large (80mm) spotting scope with a high zoom at dusk. As you zoom in you can really tell the immage gets darker as you narrow the field of view.
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