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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
40 v 50 v 56 mm Objective Lens
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<blockquote data-quote="700" data-source="post: 77209" data-attributes="member: 674"><p>Big_Bore / Buffalobob </p><p></p><p>Two factors affect twilight resolution.</p><p></p><p>1) Light gathering (brightness) capabilities of the scope which is realated to Obj. lens diameter and exit pupil.</p><p>This is calculated as </p><p></p><p>Relative Geometric Brightness = square(exit pupil))</p><p></p><p>If your eye pupil is less than the exit pupil then you substitute eye pupil in the above formula. This is because the eye pupil will have a stopping down effect on the light coming from the scope in the exit pupil. I.e. you cannot get a 8mm light beam into an eye with a 7mm eye pupil.</p><p></p><p>2) Added resolution due to increased magnification. If you can see it twice as big, then you can see it twice as clearly. This is calculated as:</p><p></p><p>Twilight Factor= square root of (mag x objective diameter )</p><p></p><p>//////////////////////////</p><p></p><p>The product of Twilight Factor and Relative Geometric Brightness might give you a better all round deal.</p><p></p><p>For a 7mm eye pupil I get the following values:-</p><p></p><p> 8x56mm scope Twilight Factor*RGB = 1037</p><p> 7x50mm scope Twilight Factor*RGB = 916</p><p> 6x42mm scope Twilight Factor*RGB = 778</p><p> 5.7x40mm scope Twilight Factor*RGB = 740</p><p></p><p>Going on these calculations, the 8x56mm has 40%% more capability than the 5.7x40mm.</p><p></p><p>This is all completely accademic for the following reasons:-</p><p></p><p>1) Even people who have the same eye pupils, their eyes may differ internally in other ways. Some might benifit more from brightness than mag., and for others the reverse might be true.</p><p></p><p>2)I assumed the scopes are of similar design and optical quality. I.e different models of the same brand.</p><p></p><p>3)The user does not wear corrective glasses/contacts. They eye pupil may have to be measured taking into account the effect of the glasses/contacts. Talk to your Doc about that. Let me know what he says.</p><p></p><p>The easies way to find which scope suits you better is put up a target just before dusk and then compare scopes as it gets darker.</p><p></p><p>Kindest regards</p><p></p><p>700</p></blockquote><p></p>
[QUOTE="700, post: 77209, member: 674"] Big_Bore / Buffalobob Two factors affect twilight resolution. 1) Light gathering (brightness) capabilities of the scope which is realated to Obj. lens diameter and exit pupil. This is calculated as Relative Geometric Brightness = square(exit pupil)) If your eye pupil is less than the exit pupil then you substitute eye pupil in the above formula. This is because the eye pupil will have a stopping down effect on the light coming from the scope in the exit pupil. I.e. you cannot get a 8mm light beam into an eye with a 7mm eye pupil. 2) Added resolution due to increased magnification. If you can see it twice as big, then you can see it twice as clearly. This is calculated as: Twilight Factor= square root of (mag x objective diameter ) ////////////////////////// The product of Twilight Factor and Relative Geometric Brightness might give you a better all round deal. For a 7mm eye pupil I get the following values:- 8x56mm scope Twilight Factor*RGB = 1037 7x50mm scope Twilight Factor*RGB = 916 6x42mm scope Twilight Factor*RGB = 778 5.7x40mm scope Twilight Factor*RGB = 740 Going on these calculations, the 8x56mm has 40%% more capability than the 5.7x40mm. This is all completely accademic for the following reasons:- 1) Even people who have the same eye pupils, their eyes may differ internally in other ways. Some might benifit more from brightness than mag., and for others the reverse might be true. 2)I assumed the scopes are of similar design and optical quality. I.e different models of the same brand. 3)The user does not wear corrective glasses/contacts. They eye pupil may have to be measured taking into account the effect of the glasses/contacts. Talk to your Doc about that. Let me know what he says. The easies way to find which scope suits you better is put up a target just before dusk and then compare scopes as it gets darker. Kindest regards 700 [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
40 v 50 v 56 mm Objective Lens
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