Rifle Scopes: A Guide to Optics

Rifle scopes weren’t really usable until World War II, but the technology has been around since the Civil War. Even in World War II, they were limited to use by sharpshooting specialists because they were expensive and needed a special skill set. Today, rifle scopes are common on both the guns of war and peace.

They are especially popular for hunting because they make aiming much simpler. What was once a three-part action is now two parts, since scope users don’t have to line up a rear sight with a front sight. Rifle scopes are convenient and can elevate your game as a hunter. However, there are a lot of options for scopes out there. They range in magnification power from 1.5x to 80x, and in price from just a few bucks to tens of thousands of dollars. If you’re just going to use it for hunting, you don’t need anything super fancy. Blain’s Farm & Fleet will help you decide which scope is best for you.

Magnification in Rifle Scopes

If you see a scope labeled “3x,” then that scope makes your target look 3 times closer than it would with the naked eye. This scope would be called a “three power” scope, because it has a magnifying power of 3. Some rifle scopes also include a dial to adjust the power of the scope. These allow you to zoom in and out on your target.

There is such a thing as overkill when it comes to the “power” of your scope. You can only shoot so far, and a higher powered scope won’t make you shoot any further. This may seem counter-intuitive, but it’s true. If you’re not steady enough to land a clean shot on a whitetail at 300 yards with a 9x scope, a 20x scope won’t magically make you more steady. It will just give you a close up of your missed shot.

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If you buy a scope, you don’t want to have too much power. If your scope’s low power setting is for long range, you won’t be able to make the easy, short range shot when you need to. For deer rifles, a 3-9x scope is usually more than enough to get the job done on deer and still allow you a wide enough field of view to take close shots. Close shots tend to arise when you hunt with a tree stand.

If the country you’ll be hunting in is more wide open and flat, look for a higher powered scope. Also, if your prey is smaller (like rabbits or varmints), you’ll want a slightly higher powered scope. You’ll want a shorter range scope for air and pellet rifles, since they have a shorter effective range.

Lens Size in Rifle Scopes

When you see a scope labeled 3-9×40, the “40” is the front lens size in millimeters. Lens size is important because it determines how much light the scope transfers to your eye. The bigger the lens, the brighter the image will be when you look through the scope. Don’t judge or compare rifle scopes based on the “light gathering” or “light transmission” percentage on the packaging. Manufacturers use different ways to measure this and some even use specific wavelengths to boost their number. You can find a very good quality, simple rifle scope if you try to keep the lens size as big as possible and don’t go with an overpowered unit.

Exit Pupil

Another thing to consider when you buy a scope is its exit pupil. The larger the exit pupil, the easier it will be to see through the scope in low light. Also, a large exit pupil will allow you some wiggle room for the angle between your eye and the scope. Exit pupil can be calculated by dividing the lens size by the magnification. The formula is:

[Front lens size] ÷ [Magnification] = [Exit pupil size]

So, if you have a 5×40 scope, the exit pupil size is:

40mm ÷ 5 = 8mm

The bigger the exit pupil, the easier your scope will be to aim with. The higher the magnification, the smaller the exit pupil will be. That’s another reason not to go too crazy and get an overpowered scope.

Eye Relief

Eye relief is the distance between your eye and the scope where you’ll still be able to see through it. Most rifle scopes have an eye relief of about 3 inches. The more your rifle recoils, the longer the eye relief you’ll need. The longest eye relief available for most rifle scopes is 4 inches. A longer eye relief will keep the scope from coming back and hitting your face when your rifle recoils after a shot. It will also keep you from having to stretch or crane your neck as much, which can get uncomfortable after long days in the field or on the range.