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The next set of attributes have to do with optical characteristics of the scope. The clarity or resolution of the scope is determined by the quality of lenses and their coatings. Image brightness and low-light performance are determined by lenses, coatings, and the objective lens diameter versus the magnification. The exit pupil is the size of the image coming out of the ocular lens. (Ocular means it's the lens closest to your eye.) If you look at the ocular lens of a scope from a foot or more away, you will see a small area of transmitted light surrounded by black. This is the exit pupil. A larger exit pupil can provide a brighter image to the eye. The maximum size of the human eye's pupil is about 7 mm, so a scope exit pupil larger than that size has no benefit in low light. One advantage of a larger exit pupil not often mentioned is that a larger exit pupil gives more flexibility in eye position to see a full size picture. This is helpful because small head movements do not create the black fringe in the scope view. The other benefit is that it is easier to retain the sight picture through recoil so the shooter can spot his own bullet impacts.

This S&B 3-12x50mm PMII provides 120 0.1-mil clicks per turn of its two-turn elevation knob; its windage knob also has 0.1-mil clicks.
Long-range optics have to provide a mechanism to precisely specify elevation hold-over to compensate for bullet drop past the rifle's primary zero. This can be done by using demarcations in the reticle, by dialing an elevation knob, or by using a combination of those two methods. Reticle design to specify elevation can be as simple as a mil-dot, or as complicated as the Horus H-25 reticle, which has small hash marks every fifth of a mil. Elevation knobs have several properties we care about: click size, total travel, and if it has a zero-stop. For practical long-range shooting, a click size of 0.25 - 0.50 MOA, or 0.1 - 0.2 mil is appropriate. Some target scopes have eighth MOA clicks which are too fine because you'd need 250 clicks to get a 308 to 1000 yards! To emphasize the importance of this point again- the reticle and the knob clicks should be in the same units system: MOA and MOA, or mils and mils!

Next, it is important the elevation knob be able to provide enough travel to get the bullet to the maximum distance the rifle can shoot. Thirteen mils or 45 MOA is enough to take nearly any 308 load to 1000 yards. At Denver altitude, .338 Lapua Magnum takes just over 13 mils to get to 1500 yards. This is where scope tube diameter comes into play; a larger diameter tube allows more erector movement, which in turn allows more elevation.