Q: Why does it look like I am looking through a tunnel at lower power?

A : To achieve the lowest magnification level the rear erector lens is positioned furthest away from the first focal plane at the front opening of the erector tube. At this distance there is a known angle from the center focal point of the rear erector lens that extends through the widest point of the first focal plane diameter. The length and diameter of the erector tube are known dimensions that define the field of view from the lowest to highest magnification setting.

A mask is a disk that reduces the aperture of the erector tube to mitigate vignetting or “tunnel vision” effect. It can also be used to make an off center reticle appear to be centered. All critical optical and mechanical components in U.S. Optics scopes are precisely aligned to utilize the entire field of view based on the erector tube dimensions for all scope models without having to use a mask.

By not using a mask, the tunnel vision effect is apparent but marginal. The benefit to not using a mask is on the high end of magnification, which happens to be where the largest field of view possible benefits the shooter. For example, and depending on the scope model, a mask will reduce field of view at 4X magnification by 5%. At 17X magnification field of view is reduced by much as 15-20%. The trade off for eliminating the tunnel vision/vignetting effect on the low end of magnification yields a marginal performance improvement in field of view while sacrificing at the high end of magnification a significant portion of the field of view while acquiring a sight picture of a target at medium to long ranges.

Q: What is the outside diameter (OD) of my objective housing?

A: The TPAL series has 3 different objective sizes:

  • MR-10: 1.858” or 47.200mm
  • LR-17: 2.230” or 56.642mm
  • ER-25: 2.650” or 66.040mm
Q : What is the diopter range for U.S. Optics scopes?

A : Diopter range is +2 to -3.

Q : How much travel do I get with a windage stop?

A :  Only the US#3 windage knob is equipped with a windage stop. The adjustment capability of a scope can range from 5 MILs left and right or 12 MOA left and right depending on windage knob specifications.

Q: After I zero my windage knob using a windage stop can I move it back to zero?

A :  Click here to consult the TPAL manual for scope zeroing instructions.

Q: How much elevation travel does my scope have?

A :

  • MR-10: 16+ Mil, 60+ MOA – 30mm tube
  • LR-17: 20.5+ Mil, 74+ MOA – 30 mm tube
  • ER-25: 25+ Mil, 90+ MOA – 34mm tube
Q: Is there a U.S. Optics dealer in my area?

A: Click here to locate a dealer near you.

Q: Why does my reticle seem blurry?

A: Click here and consult the user manual for “reticle focusing” instrutions.

Q: Can I switch out the knobs on my scope?

A: No.

Q: My illumination knob is not working?

A: The CR2032 battery may be depleted and in need of replacement. Click here and consult the users manual for “battery replacement” instructions.

Q: Are all U.S. Optics TPAL series first focal plane?

A: Yes

Q: Do I need to lap my scope rings?

A: No, there is no need to lap or modify our rings. U.S. Optics rings have been engineered and manufactured to interface with the tube dimensions of our optics to ensure proper fit without modifications.

Q: Does U.S. Optics offer a Government/Law Enforcement/ Military discount?

A: At U.S. Optics we recognize and appreciate the hard work and especially the sacrifices made by all of our men and women in uniform. We do offer a special discount to all who have or are currently serving our country in uniform. Please call to take advantage of this special offer.

Q: What type of battery does the lit reticle use?

A: The rheostat uses a CR2032 coin type battery that is fairly common.

Q: What color anodizing is available?

A: All commercially off the shelf (COTS) optics are MIL-A-8625 Type III Hard Anodized in Matte black finish. Custom built scopes can be anodized in many different colors. Contact us directly or configure your scope online. Keep in mind that custom built scopes take a minimum of 16 weeks to build.

Q: What height ring do I need?

A: Most ring heights can be figured out based on your height base and objective diameter. If you are using a 44mm objective, most likely you will need either a “X-low” or “Low” on a bolt gun with a standard base. If you are using an AR flat top design you are going to need a “medium” or “high”. Most cases the ‘high” provides a cheek position that is a bit more comfortable, “medium” is a bit too low. 58mm objective will need a “low” or “medium’ on most bolt guns.

Q: What is the small ||dent|| in my MST-100/150?

A: This is a carefully placed dent that keeps the objective from rotating in the housing when adjusted.

Q: Why a larger tube diameter?

A: A scope with a larger diameter tube provides more space for the erector tube to move in when adjusting windage and elevation. The ability to have more erector tube movement for reticle adjustment benefits a shooter when engaging targets at extended distances.

Q: My reticle appears to have dust on it, what is this?

A: Internal surfaces of the scope body are MIL-A-8625 Type III hard anodized matte black to mitigate stray light within the scope. Anodizing particulates at times can be dislodged from the internal surfaces, depositing onto the reticle. At higher magnification levels the dust/debris is difficult to detect. As magnification decreases the dust particles become more apparent. In most cases the particle will dislodge from the reticle during the recoil cycle and will become embedded in a thin film of thread and o-ring lubricant used in the manufacturing process. Once embedded in the thin film of lubricant the particles will remain intact.

Should the particles/debris remain on the reticle, contact us for a Return Merchandise Authorization Number at (714) 582-1956.

Q: What is the EREK knob?

A: The Erector Repositioning Elevation Knob (EREK) incorporates a center screw for rough zeroing. This allows the knob to be zeroed near the bottom of its travel so that all movement of the knob is upward. The EREK utilizes either 90 or 110 positive clicks in one revolution.

Q: Why am I seeing a shadow / crescent moon shape in the field of view of your ER-25 or B-25?

A: Vignetting:
If you are seeing a shadow / crescent moon shape in the field of view of your ER-25 or B-25, the slight obstruction you are experiencing is called 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. Vignetting is only a shadow cast by the internals of the optic when the erector assembly is adjusted to an extreme position within the scopes travel. In order to avoid vignetting from a manufacturing stand point, we would have to limit the travel of our optics. However, this would have an adverse effect on the optic’s performance when it is being implemented in a long range role. If you plan on using your ER-25 or B-25 in long range applications where you will be engaging targets beyond 1300 yards, we highly suggest running your ER-25 / B-25 on a 3OMOA or 40MOA down angle base as well as to have a zeroing distance beyond 100 yards. This will enable you to zero your optic without having to push the internal adjustments to the extreme positions, thus limiting the effects of vignetting.