Riflescopes, where do I Start? (A Starter Guide to Riflescopes)
By Thomas Macarle, CEO Mac Arms LLC
O.K. you have a nice rifle. You look around for a proper scope, but don’t really know what to get, because you are so overwhelmed. There are hundreds of different scopes out there. You see numbers, letters, and different shapes and sizes. The intention of this article is to make it just a bit easier to gather some information about riflescopes.
Where do you start? Customers sometimes ask, “What scope do you think is the best?”
I always tell them, “Well, it depends on what you want to do.” Then I go into my informative speech and relay common facts about scopes. Let’s start. First and foremost rule of thumb, buy the highest quality you can afford.
Basically, there are a couple of types of scopes, magnified and non-magnified. There are of course many sizes, shapes and colors but that is usually for design purposes and personal preference.
These are indicated in the numbers of the specifications of scopes and usually printed on the box or right on the scope itself. There are variable magnification scopes, set magnification scopes and non-magnification scopes. For example, a common 3-9x40mm scope is letting you know that the range of magnification is adjustable from “3” times magnification to “9” times magnification. The “40” is usually expressed in millimeters and is the diameter of the objective lens (front lens of the scope).
Another example would be 1x29mm. This would indicate unity magnification (no magnification, or normal size) and the objective lens diameter is 29 millimeters. There are several different ranges in these numbers. From magnification of 1 to 40 times plus, with objective lens diameters from about 20mm up to an incredible 75mm. Generally, for most individual needs a 3-9x magnification is fine. What do these numbers mean for performance? Here are a couple of things to start.
No magnification to small magnification (generally about 1x to 3x) benefits:
· More light transmission.
· Larger field of view. (How much area you can see through the scope.)
· A smaller scope, thus lighter in weight and less bulky.
Good quality scopes mean, among other things, good light transmission. Light transmission is how much light is transferring through the lenses to the eye. 100% is not obtainable, since some light is lost at every air to glass surface. 95% plus light transmission is excellent, with most scopes averaging around 90% or so. This is usually nothing more than quality of lenses and lens coatings. Lenses are coated with different quality of coatings, which may add to better light transmission and durability. They are also different processes of coatings:
· Coated lenses - Usually only the outside of the front (objective) and back (ocular) lenses are coated.
· Fully coated lenses - Both sides of each lens element is coated.
· Multi-coated lenses - Multiple coating layers on the outside of the objective and ocular lenses; internal lens surfaces usually receive a single layer coating.
· Fully multi-coated lenses - Multiple layers on both sides of each lens element.
Field of View (F.O.V.)
Fields of view is nothing more than how much of the scene (surroundings) you can observe through your scope. The field of view change with magnification, becoming smaller as the magnification increases. In other words, as you increase the magnification of the scope, the less area you can observe. F.O.V. is usually expressed in feet, yards or meters at a reference distance, or in degrees. For example, a F.O.V. of 24 feet at 100 yards means that when viewing at 100 yards you can see 24 feet across of the surroundings. F.O.V. in degrees is indicating how wide a "slice" of the world you can see through your scope. The degrees remain the same at any distance.
Eye relief is a simple measurement usually expressed in inches or millimeters. This is the distance from your eye to the eyepiece (ocular lens) of the scope. This is very important in riflescopes, as rifles recoil, shoving the scope toward your eye and you don't want the scope to hit you in the eye. Most scopes have around three inches of eye relief, which is fine for light kicking rifles (rimfires, .223 and .243 caliber, for example) and some can go as much as five inches (useful for elephant rifles). Four inches is considered fine for most common calibers (.270, .30-06, .308, .300 Magnum, etc.). The point being you need a scope with more eye relief on hard kicking rifles to prevent a nice black and blue shiner.
Minute of Angle (MOA)
Minute of angle or arc is a measurement in degrees. Basically, there are 360 degrees in a circle. One minute of arc (1 MOA) is equal to 1/60 degree. MOA is usually how your scope's windage and elevation adjustments are calibrated. One MOA subtends 1.047 inches at 100 yards. (One MOA equals one inch at 100 yards, two inches at 200 yards, etc. for practical purposes.) Once you have determined your rifles point of bullet impact, you can adjust your scope so many “clicks” (MOA or fractions there of) to zero in on your target. Scopes can be calibrated differently, but many use ¼ MOA (¼ inch at 100 yards) or ½ MOA (½ inch at 100 yards) clicks to adjust for windage and elevation. Again, it basically means that for a ¼ inch click scope, if you click one time it will adjust your rifle to shoot ¼ inch in that direction at 100yards.
Riflescopes are optical devices. They use light to transmit an image through lenses, just like our eyes do. Think of the scope's exit pupil like our own pupils. The larger the exit pupil, the more light is transmitted through the optics of the scope. The formula for exit pupil is: objective lens diameter in millimeters / magnification = exit pupil in millimeters. Example: a 6x scope with a 30mm objective has a 5mm exit pupil (30 / 6 = 5). A neat way to get a look at a scope's exit pupil is to hold the scope at arms length and look through it. The "light pencil" you see through the scope is the exit pupil. Try a variable power scope at low magnification and then again at high magnification and observe the difference. More magnification equates to smaller exit pupil size, thus less light reaching your eye. Exit pupil affects a couple of things. Light transmission is less when magnification is greater. Also, the larger the exit pupil the less critical you head placement needs to be when looking through the scope.
Ah, parallax. This is always a little difficult for most people to grasp. Well, the image you see depends on your position and point of view. Let’s try a small example. Look at an object in the distance, such as a light pole. Close one eye and hold your thumb out at arms length to cover the object. Then, without moving your thumb, move your head a bit to the side. Notice that, even though the two objects (thumb and light pole) are still in the same position, your point of view is now slightly different for both objects. This is the basis for parallax. The scope's crosshair can appear to be in a certain position when in fact it is not, depending on slight variations in your head position. Parallax can affect image position more for objects that are closer to you. Another example is to look through your scope and line up the crosshairs on a specific point of an object that is not at the distance for which the scope is parallax corrected. Then, without moving the scope, move your head around slightly. Notice how the crosshairs will move against the specific point at which you aimed. If a scope has a parallax adjustment, it is used to eliminate the effect of parallax at the target distance. Scopes without a parallax adjustment that are designed for use on centerfire hunting rifles are usually focused by the manufacturer to be parallax free at about 100 yards. Rimfire scopes are typically parallax free at 50 or 75 yards.
Target scopes should be able to adjust windage and elevation very precisely, over and over, since the scope may be adjusted during a match for the prevailing wind conditions. Hunting scopes need less precise adjustments, because they are typically zeroed-in with a specific load and then not adjusted in the field. However, their adjustments should be reasonable accurate and repeatable to facilitate sighting-in. Meaning that you should be able to adjust for windage and elevation and then go back to “center” with the same adjustment in reverse. In other words, if your scope is zeroed in and you adjust two clicks left, your next shot should reflect that. (At least within the accuracy potential of you and your rifle.) Then, you should be able to adjust two clicks right and be back to where you started. This would suggest very accurate adjustments.
I hope to have shed some light on riflescopes and optics. Look for good quality scopes for you rifle, because top quality scopes give you the best possible optical performance, as well as greater durability. Economy scopes are usually deficient in one or more areas and often in all areas. If you cannot line up your sight on a target properly every time and hit it, then what good is shooting a bullet in the first place?
Copyright 2013 by Thomas Macarle and/or chuckhawks.com. All rights reserved.