Tunnel Vision

Tunnel vision is yet another one of those contentious topics where people tend to disagree. Empirically, it seems that some people are bothered by it vastly more than others. My sensitivity to tunnel effect is directly proportional to riflescope price: I am willing to forgive some of it on lower priced scopes, but if I am shelling out some serious money, I get much pickier.

What is tunnel vision? The effect is easier to witness than to describe. An extreme case of tunnel vision is like looking through a straw: the image appears far away from you and it looks narrow. The actual field of view might not be particularly narrow once you look at it carefully, but it looks narrow. This effect is frequently characterized by a thick black ring around the image, although that description is not necessarily accurate. I have seen some scopes with visible black ring around the image that had minimal tunnel effect. In those designs, the eyepiece was overbuilt and had housing so thick that you simply saw the rim of the eyepiece around the image.

Tunnel effect occurs when one of the optical systems inside the scope has field of view wider than the limiting aperture in front of it. The most common occurrence of tunnel effect is due to the relay system seeing the inside of the metal tube that houses the erector lenses. On variable scopes, it is manifested by tunnel vision appearing at lower magnifications. It is not uncommon for a scope to be completely free of tunnel vision for the upper 70% of its magnification range, only to have the effect become progressively worse in the lower 30%. If you notice the black ring around the image become progressively thicker as you dial magnification down, then the relay system is at fault.

The strength of the tunnel effect is determined by the optical design of the riflescope and by how you perceive it. That is one of the reasons you have to get your hands on the scope and look through it. There is nothing in the specifications or anywhere in the accompanying documentation that will tell whether this model has tunnel vision and, if yes, its severity.