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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
eye relief margin
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<blockquote data-quote="LouBoyd" data-source="post: 342040" data-attributes="member: 9253"><p>Do a little experiment. Aim your riflescope at a target at normal distances ( 50 to 500 yards with the rifle held so the crosshairs are centered on a small target. Now move your eye from very close to the eyepiece to around twice the normal eye relief from the eyepeice. You'll see that tthe ON AXIS image changes very little. All that changes is that the field of view shrinks on either side of the "optimum" eye relief. </p><p>Another experiment. Bring your scope indoors and aim it out a window into bright sky outddoors. Put a white card at the location where you would put your eye for "normal" eye relef. You should see a bright spot on the card. Move the card a little closer or further from the eyepiece and at some distance the spot should be uniformly illuminated with sharp edges. That distance from the card to eyepiece is the optimum eye relief for that scope setting. If you have a variable power scope cnage it from minimum magnification to maximum magnification. The spot will be largest at low magnification. For any scope the diameter of the spot on the card will be equal to the entrance pupil diameter (usually the clear aperture of the objective lens) divided by the magnification. The only light from the scope which goes into your eye is in that spot.. If the spot is large than the iris of your eye some light will be lost. If you move the card closer to the eyepiece or further away you'll see that the spot gets bigger. Obviously if you have your eye in a place where your iris is smaller than the spot, you loose some light. To understand what information is in what parts of the lgiht cone you need to see a ray tracing of the light going between the eyepeice and the eye. not all locations contain the same information.. However, on either side fo the optimum eye relief the outside edges of the cone only contain light which entered the scope off axis. That's why you get the tunnel effect if you're outside of the "optimum eye relief range. </p><p></p><p>The design of the eyepiece determines the eye relief. There is always a tradeoff of apparent field of view vs eye relief for a given eyepiece diameter. You can get longer eye relief or wider field of view (or some of both) with a physically larger eyepiece. </p><p></p><p>Eye relief and eye relief tolerance have little to do with the quality of the optics. It's just a natural result of any eyepiece design You get the same reduced field effect if you move a binocular or spotting scope eyepiece away from your eye.. </p><p></p><p>You can however use any riflescope beyond it's "normal" eye relief. It just gives a tunnel effect, but it doesn't affect aiming accuracy or image brightness. It can even help accuracy as any lateral offset of your eye will be obvious. Keeping your eye centered will eliminate parallax error if the reticle is a little out of focus relative to the target.</p></blockquote><p></p>
[QUOTE="LouBoyd, post: 342040, member: 9253"] Do a little experiment. Aim your riflescope at a target at normal distances ( 50 to 500 yards with the rifle held so the crosshairs are centered on a small target. Now move your eye from very close to the eyepiece to around twice the normal eye relief from the eyepeice. You'll see that tthe ON AXIS image changes very little. All that changes is that the field of view shrinks on either side of the "optimum" eye relief. Another experiment. Bring your scope indoors and aim it out a window into bright sky outddoors. Put a white card at the location where you would put your eye for "normal" eye relef. You should see a bright spot on the card. Move the card a little closer or further from the eyepiece and at some distance the spot should be uniformly illuminated with sharp edges. That distance from the card to eyepiece is the optimum eye relief for that scope setting. If you have a variable power scope cnage it from minimum magnification to maximum magnification. The spot will be largest at low magnification. For any scope the diameter of the spot on the card will be equal to the entrance pupil diameter (usually the clear aperture of the objective lens) divided by the magnification. The only light from the scope which goes into your eye is in that spot.. If the spot is large than the iris of your eye some light will be lost. If you move the card closer to the eyepiece or further away you'll see that the spot gets bigger. Obviously if you have your eye in a place where your iris is smaller than the spot, you loose some light. To understand what information is in what parts of the lgiht cone you need to see a ray tracing of the light going between the eyepeice and the eye. not all locations contain the same information.. However, on either side fo the optimum eye relief the outside edges of the cone only contain light which entered the scope off axis. That's why you get the tunnel effect if you're outside of the "optimum eye relief range. The design of the eyepiece determines the eye relief. There is always a tradeoff of apparent field of view vs eye relief for a given eyepiece diameter. You can get longer eye relief or wider field of view (or some of both) with a physically larger eyepiece. Eye relief and eye relief tolerance have little to do with the quality of the optics. It's just a natural result of any eyepiece design You get the same reduced field effect if you move a binocular or spotting scope eyepiece away from your eye.. You can however use any riflescope beyond it's "normal" eye relief. It just gives a tunnel effect, but it doesn't affect aiming accuracy or image brightness. It can even help accuracy as any lateral offset of your eye will be obvious. Keeping your eye centered will eliminate parallax error if the reticle is a little out of focus relative to the target. [/QUOTE]
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