Scopes - Part 1
Selecting a scope
by B.B. Pelletier
If I don't get this tutorial started, we're never going to get to it, so this is the beginning. As I've mentioned before, some of this material will be used in a book I'm writing about airguns.
What will you use the scope for?
That may not be not good English, but it's a heck of a good question. If you have not used riflescopes a lot, or at all, please read this carefully. How you want to use the scope should determine many things about what the scope must have. First, let's consider magnification.
A general-purpose scope of 4 or 6 magnification (4x or 6x) is ideal for general-purpose shooting and for hunting large game (deer-sized and larger). The image seen through a scope like this is always bright and big. It doesn't "black out" with slight movements of the head. The objective lens on this scope can be 32mm and the scope will still be very bright.
Variable-power scopes are certainly more popular than fixed-power scopes today. For the general shooter a 3-9x scope has a good useful range, and once again, a 32mm objective lens allows plenty of light to pass through. A 40 mm objective lens is even better. Greater than 40mm gives such a slight improvement that it may not be worth the extra expense and mounting concerns.
Twenty years ago, scopes were primitive enough that variable power gave some cause for concern, but today a variable is as tough and useful as anything else. And the price is practically the same for fixed or variable, so I recommend a variable unless you know for sure what magnification you want and need.
If you really want a lot of power but still need a general-purpose scope, you might consider a 3-12x or a 4-12x variable. Any more power than that and the scope becomes too large to use for general shooting. It's starting to specialize. A 32mm objective lens starts to get dark or cloudy with anything above 9x, so a 40mm objective is best if the power goes up to 12x. Remember, as the objective lens size increases, the outside of the objective bell also increases and you may encounter scope mounting problems.
What size scope tube?
Scope tubes come in different diameters. One inch and 30mm are the most popular sizes today. One-inch is more common, and the larger 30mm is reserved for scopes that need more light to pass through them. A regular scope (one that isn't a night vision device) does not magnify light. In fact, a small amount of light that tries to pass through the scope is absorbed by the lenses, meaning that what is seen through the eyepiece is less light than entered the scope through the objective lens. Magnification and additional lenses rob light. Large objective lenses and larger scope tubes increase light transmission because the lenses inside the scope can also be larger.
I would like to give you a good rule of thumb for when you should go up to 30mm, but I don't have one. I have a 6-24x Tech Force variable that's pretty bright and it has a 1" tube. All I can say is that the 30mm tube allows the lenses inside to be larger, which may make a difference when the magnification climbs high. When I want a scope for use in low light scope, I always shop for one with a 30mm tube.
Specific scope uses
Field target requires a powerful scope if you plan to compete at the top levels. To determine range using the scope's parallax adjustment takes at least 40x to go out to 55 yards successfully. So, use nothing less than an 8-32x with a 56mm objective lens and a 30mm tube if you want to win.
Next, there are hunting scopes, which have to be bright. Pick the largest objective lenses and a power commensurate with what you are hunting...9-16x for squirrels; 6-12x for birds, woodchucks and large game; and 4-6x and close focus parallax for insects, etc. Deer hunters can be satisfied with 4-6x.
Airgun sillouette shooters use higher-power scopes. The handgunners use rifle scopes in the Unlimited Standing class and the Unlimited class. They do not need the power that field target competitors do, but they do use higher power than general shooters, as a rule. The Unlimited Standing handgunners hold onto the scope as well as the gun and they hold the scope close to their eye when they shoot.