In this article, we will analyze all the other features that differentiate the many scopes on the market and that must be considered when choosing the best optic for your needs.
Fixed or variable: Fixed scopes are of less complex construction. Simple construction equals more reliability, and that’s the reason why the military have used fixed scopes for decades. Modern construction process have increased reliability of variable optics however, when you are on a budget, you may consider to get a fixed scope since they are cheaper respect of their variable counterpart of similar quality. On the other hand, variable scopes allow you to fit a wide range of “jobs”, since you may need to change magnification for various reasons, such avoid mirage distortion, increase field of view, increase light transmission for twilight (not the movie) shots, or decrease wobbling perception during off hand or unsupported shooting.
Magnification: The amount of magnification we are going to need is in function of the type of shooting, the distance, and the target size. Longer distances and smaller targets require more magnification. More is not always better, since with higher magnifications you amplify optical imperfections in mid and low priced scopes, sometimes compromising your ability to aim accurately, thus the higher the magnification, the better must be the optic. Moreover, optics with more magnifications are also generally more bulky and heavier. From my experience, for target shooting at static distances (i.e. 1000y matches), varmint hunting, and extreme long range shooting, 20-25X scopes works just fine. For military style shooting, at paper targets or gongs at variable distances, or for big game hunting at long (but not extreme) range, 12-14X are more than enough.
Front lens (or objective) diameter: Larger front lenses allow more light in the scope, meaning that we should be able to shoot under lower light conditions. I’ve written “we should” because in reality light transmission is also in function of other variables like the light transmission capability of the lens crystal and the scope’s tube diameter. We can obtain a reference value of the low light capability of a scope, the so-called “exit pupil”, dividing the front lens diameter (in millimetres) by the magnification value. For example,if we have a 10×40 scope we will have an exit pupil of 40/10=4mm. Here again, more is not always better. Our pupil can receive only a certain amount of light, and that amount of light decreases with age. In addition, high exit pupil values are useful for shots in low light conditions, but when you are utilizing the scope in standard light conditions (i.e. in the middle of the day), the great amount of light that you receive can prematurely strain your eye. Wider objectives also force you to mount the scope higher over the barrel line, forcing you to stay higher with your head and increasing the errors due to rifle canting. From my experience, for hunting purpose, where you are likely to shot in low light cnditions, a good 50mm is enough. For target shooting, a 50mm is still good but even a 40mm will do the job.
Field of view: also indicated with the acronym FOV, is the amount of view that you can see through your scope at a given distance. It is indicated in ft@100yds (feet at 100yds) or m@100m (meters at 100m). The amount of FOV of a scope is determined by the internal construction of the eyepiece. It is an important parameter to consider when choosing a scope for hunting or dynamic shooting purpose, since a wider field of view may help in tracking a moving target as well as spotting multiple targets in the same area and eventually following their movements.
Tube diameter: The scope’s tube is the cylindrical part of the scope between the eyepiece and the turret and between the turrets and the objective cone. Its diameter is indicated in millimeters (the diameter of 25mm is indicated as 1”), and it is a crucial parameter for the selection of a scope. Wider tubes allow more light transmission and, generally, a higher amount of adjustment. In the past, almost all the rifle scopes on the market came with a 25mm (or 1”) tube. Today, many brands offer 30mm tubes with some offering 34mm and 40mm (like the IOR Valdada).
Eye relief: When watching through a telescopic sight, there is only one distance, from the rear lens, from which the eye can see a full perfect picture. That distance is the eye relief. Its value is expressed in inches or millimeters, and for rifle scopes it is generally in the range of 3 to 4 in. Generally, it is related to the scope’s magnification, with higher magnifications scopes having shorter eye relief, but that’s not a rule. When choosing the scope, eye relief may be taken into consideration only when the scope is mounted on rifles with heavy recoil, since a short eye relief could be dangerous for the shooter. To be honest, a difference in eye relief of 1” is not that big difference. To avoid the famous “scope kiss”, a proper technique helps a lot more than that inch.