TA31H-G problems

[Webbie13]

I have a TA31H-G and the right 40% of the scope appears to be blurry and out of focus. However, I am at a loss because I bought the scope used so the warranty does not cover it. Have any of you experienced similar problems? Should I try to get the original owner to contact Trijicon? It's pretty upsetting to see such a problem on a scope with only about 100 rounds through it.

[Webbie13]

Whoops. I'm an idiot. Here is the info from Trijicon if anyone else is wondering.

The right hand side of the crosshair is blurry. Is this normal?

Yes. The reticle pattern in the ACOG is formed by removing highly reflective metal from a prism mirror. This mirror is at about a 45-degree angle inside the gun sight. This means that the left side of the reticle is closer to the eye than the center of the reticle and the right side of the reticle is further from the eye. The result- the right side of the reticle is focused beyond infinity which can cause distortion on the right side of the reticle. The perceived distortion will be more or less depending on an individual's eyesight. The left side of the reticle is unaffected because the human eye has no difficulty focusing on a closer object. This in no way detracts from the performance of the scope. The image of the target area is not affected. Only the right hand side horizontal reticle line is blurry. This construction is required to achieve a parallax free vertical center of the scope, which allows the built in ranging on the reticle pattern.

[Hochsitz]

Yeah that's an inherent design issue with the ACOG type optics. They shorten the overall length by folding up the optical path inside a prism and use one of the prism faces for the rear focal plane. Conventional optics look THROUGH the reticle, the ACOG looks "at" the reticle. It would be like drawing a reticle pattern on your bathroom mirror. Besides shortening the length of the optic, it also makes it really easy to back illuminate with an external light source like tritium or the fiber optic tube run along the exterior of the housing. The down side is exactly what they've described. Your focal plane is not parallel to that surface of the prism so it's impossible to get all of the reticle at a single diopter. Young guys with flexible eyes can accommodate for much of it but older users will see a reticle that is only focused in one area and not necessarily in the middle! That combined with a fixed diopter (no adjustment) leads optics snobs to describe it as a piece of garbage. If that's true, it's an extremely successful piece of garbage.

When Trijicon introduced the sight they used a reticle with long horizontal scales for range estimation plus holds for wind and moving targets. However after receiving complaints like yours they started deleting the long horizontal features so the effect would be minimized. Another bizarre behavior is that those long lines appear to swim like little paddles as you move your eye around the eyebox.

If you want to really see something interesting, fix the ACOG in a bench vise so it can't move but you can still see a distant object through it. Now start turning the adjustments and try to align the reticle with some feature on your target. Any time you change directions or switch from horizontal to vertical you'll get a jump or some other undesirable shift. In my experience it eventually "settles in" but turns what should have been a brief sight-in session into an exercise in consuming ammo.

What the ACOG does really well is to be rugged enough that it's difficult for a soldier to break yet simple enough to mass produce. They serve that purpose well and have dominated the low mag military carbine market for more than a decade.

I'm curious what the future holds for this product as the market becomes over-saturated with 1-6 options with more features but also increased complexity. The military has essentially decided to drop the ACOG in favor of a yet to be identified variable platform known only as the Squad Common Optic (SCO). The ACOG had a fantastic run, something all the optics manufacturers desperately want to replicate.