When choosing a rifle scope today, there are more options than ever before. It is important to have an understanding of each to make a clear and timeless choice. Let's talk about rifle scope terms you need to know.
That term means nothing by itself, but since the earliest parallax adjusting scopes put the adjustment feature into the rotating objective bell of the scope, the term AO appeared. An adjustable objective is a dial around the objective end of the scope that allows you to adjust your scope parallax to a certain distance by moving these adjustments until a clear picture is perceived. The correct setting of an adjustable objective helps to prevent a change between the reticle and the target when the shooter moves his head off-center of the rifle scope.
We all know that powerful spring-piston airgun recoil can destroy non-airgun rated scopes in only a couple of shots. That's why airgun scopes were invented: to withstand the dual-recoil of spring-piston airguns.
Exit pupil is a very important factor in light transmission of an optic and something that is generally ignored or misunderstood by a lot of people. It controls the brightness of the image that will be viewable to your eye. It is visible in the eye lens when you hold the scope at arm's length.
Eye Relief is a space that affects how full you'll see the view of the scope. Typical scopes offer around 2 ½ - 3” eye relief.
Field of View
Field of view is an actual image that you're seeing when you look through your scope. The distance from one edge of the circle to the other is the field of view. If you have set it wrong for your eyes you could see a fuzzy black edge t closing the view.
Kentucky windage is the point that helps you to set for wind effects on your projectile. It allows you not to reset your scope.
You'd see something with the naked eye differently. A wide field of view and a lot of things around. Magnification helps to narrow the field of view. Magnification is the size of an image relative to the size of the object creating it.
Maximum Point Blank Zero
Blank zero is the elevation and windage settings required to engage a point target from zero to your max point-blank range under ideal weather conditions. In order to find the max point-blank range, you should take into account the ballistic coefficient of the round, the muzzle velocity, and the sight height of the gun. This is good for guns that have higher sights or optics that don't have an elevation compensator.
The muzzle is the front end of the barrel from which the bullet exits.
Minute of Angle
A minute is just a fancy word for one-sixtieth (think about 60 minutes in an hour). Well, that's the same as saying one minute of time is a sixtieth of an hour. This minute is gonna be the sixtieth of the angle that is on the circle of 360 degrees. So, the sixtieth of one of those degrees is one minute of angle. It ends being about 1.0400 inches at 100 yards.
It's not a size at a certain distance but rather it's an angle that we're making in the scope that ends up translating to a certain size at a certain distance.
The objective lens is one of the most important parts of the optical system. An objective lens is the lens closest to the object being viewed. It usually has a lot of numbers and letters but not every person knows what they mean. A first number is a whole number (magnification of an objective). A next number is a decimal number that means a numerical aperture for the light gathering ability of the lens. It is measured in millimeters in diameter.
An ocular lens is a lens that is closest to your eye.
Parallax is the apparent setting of the reticle on the target image at different ranges. When we are shooting we are dealing with three different planes (the eye, inside of the rifle scope, and the target). Parallax errors start to come into play when your head and your eye start to move off-axis a little bit over to one side.
A reticle is a system of lines, dots, or crosshairs in your scope that appear superimposed on your target. The most common design you'll see is a rear focal plane or second focal plane design. It is placed behind the magnification adjustment that means when you change your magnification, grow the size of your target or shrink the size of your target your reticle size never changes and always stays the same size.
The front or first focal plane does the opposite. It puts the reticle in front of the magnification adjustment. So when you grow your magnification not only does your target size get bigger or smaller, your reticle size gets bigger or smaller in the same way.
The trajectory is a path of body as it travels through space or to be more clear, it's the flight of your bullet after it leaves the barrel.
Twilight Factor is a geometrical calculation of how bright a particular optical product is. It basically means a square root of the multiplication of magnification and objective lens diameter. Twilight factor helps to compare different optics and determine which one will be better in low light. Many years ago Twilight factor was important to determine which optics will perform better in low light but nowadays there are geometrical calculations used instead.