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What the numbers on your scope mean.

Discussion in 'General Gun Discussions' started by PinnedAndRecessed, Aug 16, 2006.

  1. PinnedAndRecessed

    PinnedAndRecessed member

    Aug 10, 2004
    I don't remember where I got this, but it's a pretty decent explanation of scope nomenclature.

  2. arthurcw

    arthurcw Member

    Mar 10, 2006
    Houston, TX (a.k.a. Free City of Aztlan)
    thanks. that was very helpful. :)
  3. brickeyee

    brickeyee Senior Member

    Feb 25, 2005
    “…still maintain a 8mm exit pupil, ensuring that your eye has as much of the light that comes out of the scope that it can use…”

    This is sort of correct, and sort of misleading.

    Your eyes pupil size will limit the beam to whatever size it is at. If the pupil of the eye is 7mm, you are throwing away light gathered by the scope (the “it can use”).
    This will result in a dimmer view than if the scope exit pupil was made smaller and no light blocked by the eye pupil.

    In optics the smallest opening sets the brightness. In this case the pupil.

    Even the optics books rarely discuss the effects of an eye pupil being smaller than an exit pupil. You are sort of left to ponder what is going to happen.

    Ideally as long as the eye is slightly larger than the exit pupil you will get all the light the scope can gather.
    A smaller eye pupil discards light.

    Pupil size is also not always 7mm. Many folks only run in the 5mm range unless chemically dilated.
    Ask you eye care person to measure your dilated pupil (without chemicals) is you want to know.

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