Whenever you see rifle scopes, they have numbers that give us information about them. The typical format is (power – power x objective diameter). The first power number, to the left of the hyphen, is the minimum magnification limit or level; the second power number, to the right of the hyphen, is the maximum magnification limit or level; the third and last number is the diameter of the objective lens in millimeters.
Numbers on a Rifle Scope Explanation:
1st Number (left of the hyphen):
Let’s start with the power range first. Power range is also known as magnification levels, which gives us a fair idea of what it is. A magnification level is simply the level at which the object would be magnified compared to the naked eye. For example, 2x scope or “2 power” would mean it is magnified 2 times the size of the naked eye. Similarly 3x scope would be three times, 7x scope would be 7 times and so on.
Second Number (right of the hyphen):
The second number is the upper limit of the magnification level. For example 4-10×50. The two numbers show that it is a zoom lens or scope. The shooter can set any number between the two limits according to the need. Most scopes today have variable range. However, sometimes there is only one number. In that case, the scope stays fixed at the specific level of magnification and is unchangeable.
Third Number (the diameter):
The third number is the diameter of the objective lens; the end closest to the barrel. According to the principles of lenses and light, a bigger objective lens allows more light to pass through the lens, helping increase low light performance and clarity of the scope. So a 50 mm scope would have better brightness and clarity than a 20 mm lens.
Next up is tube diameter. It is also a variable that needs to be considered when buying rifle scopes. The tube diameter is measured from the central part of the scope tube. The two common sizes are 1 inch and 30 mm diameters. The former is most commonly found, with the latter being found in some European products, is increasing with time too. Contrary to popular belief, the diameter doesn’t have anything to do with the allowance of light in the tube. It is helpful in giving more strength and rigidity to the rifle scope, due to the greater cross-sectional area. It also helps in having better windage and elevation adjustments.
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Field of View (FOV):
Field of view (FOV) is another important aspect in scope buying. As the name implies, it is the extent of the observable world from the human eye or any optical device. In the case of rifle scopes, it is measured in feet or degrees at specific yardage. The power of the scope has an inverse relationship with FOV; as the magnification increases, the FOV decreases. One has to trade off one for the other. A bigger FOV is better for acquiring targets or following moving targets. An example of FOV is 100-150 ft @ 1000 yards and 1.5-3.1 degrees @ 1000 yards
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