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Scope Guide
Choosing the appropriate rifle scope is a pivotal decision that directly influences shooting accuracy, consistency and overall performance. Modern optics vary widely in design, functionality and intended application by encompassing everything from lightweight hunting scopes to precision engineered long-range systems. Understanding the terminology of a scopes key specifications is essential and will help you to make an informed choice. This guide, created by our in-store team at NEO in London, provides a brief overview of the fundamental terminology and considerations when purchasing a scope.
If you have any further questions, get in touch via our contact details and a member of our team will assist you.
What is Parallax?
Parallax in a rifle scope is the apparent movement of the reticle across the target whenever you move your eye. If parallax is present, the reticle will seem to float or shift over the target even though the rifle itself hasn’t moved.
This means your point of aim isn’t the same as your point of impact, which is a small but significant error and has a detrimental effect on your accuracy.
At short range, even small parallax errors can cause noticeable misses, especially on smaller targets. At long range, the same error causes a smaller shift on target, making it less significant but an error nonetheless. There are two types of scopes, Fixed Parallax (e.g. Fixed at 100 yards) and Adjustable Parallax (e.g. 25 yards to infinity).
What’s the difference between Fixed and Adjustable Parallax?
A scopes parallax setting is the distance at which the reticle and the target image are optically on the same focal plane. At that distance, when you move your eye, the reticle will not appear to move. However, if the target is closer or further than that distance, even a small shift of your head can make the reticle appear to move on the target – this what is called a parallax error.
Fixed Parallax, e.g. Fixed at 100 yards:
This scope is optimised for that distance (100 yards) and targets up to and beyond that will appear with a noticeable parallax error if you move your eye. These scopes are not generally ideal for air rifles. Since most airguns will fire at distances up to a maximum of around 70-90 yards, if you use a scope with Parallax fixed at 100 yards, you won’t ever be able to avoid or correct the parallax error.
Adjustable Parallax, e.g. 25 yards to infinity:
This scope is enables you to adjust the parallax to suit targets at any target from and including a minimum distance of 25 yards. These scopes are ideal for air rifles, as you will be able to fire clearly at close range targets and also adjust the parallax to suit targets further away.
What does “infinity” actually mean?
Infinity refers to targets at extremely far distances, e.g. up to hundreds of thousands of yards away.
What does MOA mean?
MOA stands for Minute of Angle. When a scope says MOA, it’s telling you what measurement system the scopes adjustments and reticle markings use. A Minute is a unit that divides an angle:
1 degree = 60 minutes. Therefore, 1 MOA = 1/60 of a degree. Because it’s an angular measurement, it spreads out over distance. For example, at 100 yards 1 MOA = 1.047 inches (commonly rounded to “1 inch at 100 yards”)
MOA is used on scope turrets and reticles to make precise elevation and windage adjustments. For example, a scope with ¼ MOA clicks moves your point of impact 0.25 inches at 100 yards per click. Why do you need to know this? So you can zero your rifle correctly, make precise corrections for pellet drop or wind and understand ballistic charts that list drop/wind drift in MOA.
What does MRAD mean?
MRAD stands for Milliradian (often shortened to “mil”). Like MOA, it’s an angular measurement. Both MOA and MRAD do the same job, they just use different scales. Essentially, MOA is operators who use inches/yards and MRAD is for operators who use metric (centimetres and metres). See the comparison chart below:
| Feature | MOA (Minute of Angle) | MRAD (Milliradian) |
| System | Imperial (inches/yards) | Metric (centimetres/metres) |
| 1 unit equals | ~1 inch at 100 yards | ~10 cm at 100 metres |
| Turret clicks | Usually ¼ MOA per click | Usually 0.1 mil per click |
| 1 full unit equals | 1 MOA ≈ 1.047″ @ 100 yd | 1 mil ≈ 3.6″ @ 100 yd |
What do the numbers on the scope mean? For example, a 3-9×40 Rifle Scope.
The 3-9 part refers to the magnification. 3 means the target will look 3x closer than your naked eye, whilst 9 means the target will look 9x closer. You can adjust the magnification anywhere between those numbers using the zoom ring to suit your specific needs.
The 40 part refers to objective lens diameter. This means that the front lens (the opposite side of the scope to the one you look into) is 40mm wide. The larger this number, the more light the lens lets in. Larger lenses are generally better for darker environments and harsher weather conditions such as heavy rain.
What type of reticle should do I need?
There is no simple answer to this question, as this is almost entirely dependable on your own preference. To help you make an informed choice, we have created a comparison chart below:
Simple/Traditional Reticles (shaped liked a “+” symbol)
| Reticle | Description | Use / Advantage |
| Duplex | Thick outer lines tapering to fine centre crosshair | Most common hunting reticle; fast to acquire target, simple and clear |
| Crosshair | Thin lines throughout | Very precise for target shooting at longer distances |
Range/Precision Reticles
| Reticle | Description | Use / Advantage |
| Mil-Dot | Dots spaced in milliradians along the crosshairs | Range estimation, holdovers for elevation/wind; standard in military/long-range scopes |
| MRAD / Mil Reticle | Similar to Mil-Dot but with hasher marks along vertical/horizontal | Precise measurement in metric units; long-range |
| BDC (Bullet Drop Compensator) | Series of marks or dots below the centre line | Lets you aim for different distances without adjusting turrets; common for hunting |
| Christmas Tree / Grid Reticle | Hash marks forming a grid below centre | Precise elevation & windage holdovers for extreme long-range shots |
| Horntail / Mil-Cross | Combination of crosshair and mil-dot/grid | Tactical and sniper scopes; precise aiming and range estimation |
Tactical Reticles
| Reticle | Description | Use / Advantage |
| Red Dot / Tac-Dot | Single illuminated dot at centre (sometimes with circle) | Extremely fast aiming at close range; common in AR rifles |
| Holographic | Projected reticle in holographic sight | Speed and precision; can aim with both eyes open |
| Circle-Dot | Dot inside a ring | Helps with rapid target acquisition and holds well on moving targets |
| Tactical Chevron/Triangle | Small triangle or chevron as the aiming point | Quick visual reference, often in competition optics |
Hybrid Reticles
| Reticle | Description | Use / Advantage |
| Illuminated Reticles | Any reticle type with illuminated centre | Excellent in low-light or dusk conditions |
What is AO?
AO stands for Adjustable Objective and it is closely related to parallax adjustment. AO is a type of adjustment on a rifle scope, usually on the front (objective) lens. Its primary purpose is to correct parallax at different distances, ensuring the reticle stays on target even if your eye moves slightly. By turning/adjusting the AO, you focus the objective lens for a specific range (e.g., 50 yards, 100 yards or 300 yards).
How is AO different from Parallax Adjustment?
These two things are commonly confused with each other. Remember, Parallax is a problem that occurs when the reticle appears to move against the target when you move your eye. AO (Adjustable Objective) is one way to correct this problem.
What is Tube diameter and why is that important?
You need to know this in order to buy the correct mount rings for your scope. For example, if your scope has a 30mm tube, you will need 30mm mount rings. You must buy mount rings from a reputable manufacturer, do not try to cut costs on anything related to firearms. Find a trusted manufacturer that offers some kind of warranty and take professional advice/instructions into consideration.
First or Second Focal Plane, what does this mean?
Modern rifle scopes place the reticle (the crosshair or aiming dot) on one of two internal optical planes, either on the First Focal Plane (FFP) or the Second Focal Plane (SFP). This affects how the reticle behaves as you change magnification. In a First Focal Plane scope, the reticle changes size as you zoom in and out. In a Second Focal Plane scope, the reticle stays the same size regardless of magnification. For Air Rifles, we generally recommend the Second Focal Plane (SFP).