Why does it look like I am looking through a tunnel at lower power?
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.
What is the outside diameter (OD) of my objective housing?
The TPAL series has 3 different objective sizes:
B-10:  1.9” (49.4mm)
B-17:  2.3” (58.4mm)
B-25:  2.38” (60.48mm)

TPAL Series:
MR-10/ST-10:  1.858” (47.2mm)
LR-17:  2.230” (56.6mm)
ER-25:  2.650” (66mm)

What is the diopter range for U.S. Optics scopes?
All U.S. Optics scopes have a diopter range of +2 to -3
How much travel do I get with a windage stop?
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.
After I zero my windage knob using a windage stop can I move it back to zero?
Click here to consult the TPAL manual for scope zeroing instructions.
How much elevation travel does my scope have?
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
B-10: 28 Mils, 100.8 MOA – 34mm tube*
B-17: 24 Mils, 86.4 MOA – 34mm tube*
B-25: 22 Mils, 79.2 MOA – 34mm tube*
*B-10 and B-17 scopes are set for 20 MOA down and B-25 scopes are set for 30 MOA down. Therefore, all listed travel specifications are applicable to factory settings.
Is there a U.S. Optics dealer in my area?
Click here to locate a dealer near you.
Why does my reticle seem blurry?
Your diopter might not be in focus to your eye’s prescription. Please consult the instruction manual (Reticle Focusing) to set your diopter.
Can I switch out the knobs on my scope?
U.S. Optics currently does not offer the option to retrofit scope post-production.
My illumination knob is not working. What should I do?
Your battery is most likely drained. Replace the current battery by following the instruction in the user manual. If replacing the battery does not fix the issue, the rheostat might not be making contact and therefore may be causing a short. Please give us a call and we will send you a replacement.
Are all U.S. Optics TPAL series first focal plane?
Yes, all past and current models are FFP.
Do I need to lap my scope rings?
No, there is no need to lap or modify your U.S. Optics scope rings. Our rings are engineered and manufactured to interface with the tube dimensions of our optics to ensure proper fit.
Does U.S. Optics offer a Government/Law Enforcement/ Military discount?
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.
What type of battery does the lit reticle use?
The rheostat uses a CR2032 coin battery. This battery is very common and can be purchased at your local hardware store.
What color cerakoting is available?
All of our off the shelf optics are Type III Hard Anodized in Black. Custom built scopes can be cerakoted in many different colors. Please see the options listed in the scope configurator page. Keep in mind that custom scopes take a minimum of 16 weeks to build.
What height ring do I need?
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.
What is the small ||dent|| in my MST-100/150?
This is a carefully placed dent that keeps the objective from rotating in the housing when adjusted.
Why a larger tube diameter?
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.
My reticle appears to have dust on it, what is this?
This is not common, but occasionally occurs. If you see dust at lower magnifications, please contact us for a Return Merchandise Authorization number (828) 874-2242.
What is the EREK knob?
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.
Why am I seeing a shadow / crescent moon shape in the field of view of your ER-25 or B-25?
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.
Where are U.S. Optics scopes made?
All U.S. Optics scopes are designed, engineered, and developed by our talented engineers located in Connelly Springs, North Carolina. Our Foundation Series line of optics are domestically manufactured and assembled in North Carolina. Our TS-Series and Electronic Sights are manufactured overseas and imported to our facility for quality assurance. Each and every product, domestic and imported, go through rigorous testing prior to shipping.