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Old February 21, 2013, 12:23 PM   #11
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
stubbicat, you're just fine without a range-focus/parallax adjustment. With the lower power scopes (typically 6X and under), it's not a big problem as they're usually focused at about 100 yards. While they may well have a 1/2 MOA error with ones eye at the edge of the field of view when the target's 50 yards away, you'll miss your aiming point by only 1/4 inch.

I got to thinking last night that it would be nice if rifle scopes had an autofocus system like modern cameras. With present technology with such things, a 10X scope would need a lens at its front at least 3.5" in diameter for it to work. If on a 20X scope, the front lens needs to be 7" or more. Imagine how high the aiming eye would have to be off the butt stock to look through that scope. To say nothing of the mount height above the bases to let that scope clear the barrel.

I've contacted several scope makers over the years suggesting they get a qualified technical writer to put instructions in print and pictures so folks could easily understand what they need to do for best scope performance. None of them's done it as far as I can tell. Nightforce has pretty good instructions:

But they messed up in the section on adjusting the eyepiece to focus on the reticule:
If adjustment is necessary, follow the steps outlined for the type of Nightforce riflescope you have. Due to the way the human eye focuses, best results are usually obtained by turning the eyepiece inward until the reticle is slightly blurred then moving it outward until sharp focus is obtained. Refer to Figure 1.
It's not about the way human eyes focus. It's the way the eyepiece lens focuses. It's identical to a camera lens depth of field; things are in good focus twice as far beyond the focus distance than in front of it. The eyepiece lens' job is to make the reticule appear at infinity so your eyes will be relaxed and have a clear view of it. When you move the eyepiece, its focus point moves with it and you need to put that point right on the reticule.

Such errors in explaining optics makes all sorts of folks start thinking incorrectly. And that leads to getting confused with other things.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master

Last edited by Bart B.; February 21, 2013 at 12:57 PM.
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