Many people come into our store here with the hopes of finding a great new scope for their rifle only to walk up to the optics counter and become confused with all the terminology and numbers. First off, we're here to help! Don't be afraid to ask questions or ask for an explanation. In this write-up, we're going to try to lay out what the numbers mean and what each term that you may hear is referring to when it comes to optics. We won't go into great detail, we just want to cover the basics.
If you've ever purchased a scope, certainly you've seen a set of numbers similar to 3-9x40 or 6-24x56 AO or 2.5-10x44 IR. So what do these all mean? Essentially, what your reading is: (minimum zoom) to (maximum zoom) and the size of the (objective lens) or (min zoom)-(max zoom)x(obj lens). Looking at the second example above, the AO will stand for Adjustable Objective and in the third example IR stands for Illuminated Reticle. The reticle of course is sometimes better known as the "crosshair" or "crosshairs" by some folks. You should also see on the box a number like 1" tube, 30mm tube, or less commonly 34mm tube or even 36mm tube.
Why are these numbers important to you? Let's take a look below:
- Minimum Zoom - This is the lowest magnification power you will be able to achieve with this scope. If you're shooting targets relatively close to you, you may want this number to be pretty low. In the first example above, at the lowest magnification on the scope, your target will appear 3x closer than with the naked eye.
- Maximum Zoom - This is the highest magnification power you will be able to achieve with this scope. If you're shooting long distances, clearly you're going to want a pretty high number here. In the first example above, at the highest magnification on the scope, your target will appear 9x closer than with the naked eye.
- Objective Lens - Generally the bigger this number is, the larger "picture" you're going to be able to see when looking through the scope. You'll also hear some people call this the "bell" of the scope. For instance, in the first example above that scope has a 40mm bell.
- Tube Diameter - This is how large the main body tube is between the eye piece and objective lens. The larger this tube is, the more light the scope can gather in most cases.
- Illuminated Reticle - This one is fairly obvious. This indicates that the reticle of the scope can be illuminated for low light situations. Most illuminated reticles are going to be red in color, but green is also quite popular and occasionally you'll see a blue reticle (which is actually quite helpful for some folks that are color blind) or a yellow reticle on optics such as reflex sights.
- Adjustable Objective - This allows you to focus your scope on targets at differing ranges. You'll also hear this called adjusting the parallax. Side note: some scopes have a parallax adjustment on the side of the scope and it's often designated by SF for Side Focus.
- Focal Plane - Scopes can be offered with either a First Focal Plane (FFP) or more commonly Second Focal Plane (SFP). Your average scope has a Second Focal Plane and you'll notice when adjusting the power ring for your magnification, the reticle appears unaffected. On a First Focal Plane scope, as you adjust the magnification higher, your reticle will also enlarge as you zoom in on your target.
- Turrets - Turrets are the "caps" you see on the side and top of your scope in the center of the main body tube. These allow you to adjust for windage and elevation and in turn affect where the bullet will impact on the target in relation to where you're aiming. On a scope that you typically only use for hunting, the turrets are usually only utilized when "zeroing in" your scope. Most hunting scopes have the turrets capped so they don't accidentally get moved and throw off your shot. Target or Tactical turrets typically are uncapped and allow you to "zero" the scope and lock in those settings at "zero" on the scope. Then since the turrets are uncapped, you can use the turrets to quickly adjust for wind or elevation on longer or shorter distance shots and then return your scope to the "zero" you set previously.
What to keep in mind when you purchase your next scope that we haven't already covered?
- Make sure when you purchase the rings to mount your scope that you know what size your tube is on your scope. This is critical because only the right size will work, there's no "making it fit" for the most part.
- Be careful with your objective lens, it may seem like bigger is better, but at some point the "bell" on your scope is going to touch your gun barrel and that is not going to be good for you. While rings are offered in Low, Medium, High and even Extra High heights, the closer your scope is to your gun barrel, the better off you're going to be when shooting.
- An illuminated reticle can be great for you, but remember to turn it off or prepare to keep spare batteries handy. In most cases the battery is going to be a CR2032 or CR1632.
- Be mindful of your scope’s magnification as well. The higher magnification you "zoom in" to, the smaller the picture you're going to see and the scope is going to become more sensitive to movement and appear shaky.
- The bigger and more features the scope has can be perfect for some shooters, but typically they add weight to your scope and those ounces can be precious on long hikes through the woods or when trying to hold steady on that monster buck across the field.
- Some scopes have reticles that are specific to certain calibers or guns such as slug guns or muzzleloaders.
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