It’s physically impossible for a scope to be perfect at its extremities because when dialled at this level of elevation or windage, the light that is coming through is bending. This is physics. And it’ true term is ‘Vignetting’.
Vignetting only occurs at the extreme adjustments of the optic’s available travel (both in windage and elevation) due to the fact that the erector assembly is positioned at an extreme up/down/left/right position.
When the erector assembly is in this extreme position, there may be a visible obstruction of the light-ray-trace pattern. The extreme positioning allows the edges of the focusing tube to slightly obstruct the light-ray-trace which will cause a ‘shadow’ or ‘crescent moon shape’ to form in the field of view.
When you run though the adjustment on your optic, as if you are dialing up for longer distances, the erector assembly will no longer be in an extreme position, which will cause the vignetting to disappear from the field of view. Vignetting is not a defect in your optic, nor is it something that will cause any form of optical or mechanical malfunction.
In order to avoid vignetting from a manufacturing stand point, one would have to limit the travel of their optics. However, this would have an adverse effect on the optic’s performance when it is being implemented in a long range role.
(Words: U.S. Optics)
To do away with the vignetting saga, a brand new (and much more reliable alternative to ‘frequently-moving-the-reticle-of-your-scope-around’) mounting system has been manufactured:
Minute of Angle Base/Mil Radian Adjustment Base or M.O.A.B./M.R.A.B.
When installed on your rifle the M.O.A.B./M.R.A.B allows the shooter to compensate for the trajectory drop of their bullets in a mechanical way rather than optically. By doing so it eliminates unnecessary wear inside the scope; it provides you with a greater range of adjustability; and reduces the occurrence of VIGNETTING!
The M.O.A.B/M.R.A.B system is used in conjunction with a normal full length MIL-SPEC M1913 Picatinny rail. When in place it allows the shooter to dial-in their scope by simply turning an index dial located at rearmost portion of the M.O.A.B./M.R.A.B.
CLICK HERE to order your M.O.A.B/M.R.A.B now and do away with vignetting once and for all.
Click the link below and watch from 02:40 for brief explanation of Vignetting/Optical Degradation from the guys at Zero Compromise Optic.