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How To Choose a Rifle Scope:
All of us work hard, so when we get a chance to enjoy ourselves by pursuing our hunting or shooting hobby we don’t want to be saddled with equipment that doesn’t do the job. You want a quality rifle scope that will do what you need it to do without paying too much.
So how do you go about choosing the scope that’s right for you? It all depends on the type of shooting you’re doing, the type of gun you’re shooting, and personal preferences of features like color and reticle type.
We’ll go through some of the basics that apply to rifle scopes, shotgun, muzzle loader and pistol scopes. Once you understand the basics of a scopes’ anatomy and how it works you will be able to choose the best scope for you.
What do Rifle Scopes do?
Simply put, rifle scopes magnify an image and put your eye on the same optic plane as the image you are viewing. Scopes magnify an image by bending light rays through a series of lenses within the scope. The laws of physics being what they are, lower powered scopes are typically shorter and have smaller lenses than higher powered scopes.
All rifle scopes have a reticle like cross hairs, a dot, a post or similar markings built in to reference the center of the field of view seen through the scope.
If you have ever used open sights you know you have several things to worry about at the same time: Is the front blade properly aligned with the rear for both elevation and windage? Yup, they’re lined up, but the target is a lot further away from your eye than the sites are so it’s out of focus. Ok, I’ll focus on the target instead, d’oh, now the sites are out of focus! It takes a lot of practice to reliably shoot open sites well.
A scope eliminates those problems. You focus on the target and align the center reference point where you want your bullet to hit (provided your scope is “sighted in”, more on that later) and pull the trigger. That’s it.
A rifle scope also allows you to see the target better through magnification. This allows for a more precise placement of where your shot goes. Humane kills while hunting or shooting the bulls eye of a target is far easier with a scope.
Rifle Scope Anatomy and Terminology
1) Eye Piece
The metal assembly that holds the Ocular lens and is attached to the eye-bell
2) Ocular Lens
The lens closest to your eye
3) Eye Relief
The distance from your eye to the ocular lens when you can see the “full field” of view. You want a rifle scope that offers generous eye relief so the recoil of your gun doesn’t give you a black eye (this can happen!) but also allows for a large site picture.
4) Eye Bell
A housing that the eye piece and tube gets attached to.
5) Power Ring
A variable power rifle scope will have a ring you can rotate to change the magnification of the scope. When turning the ring you are changing the distance the internal lenses are from the objective lens, therefore changing the amount the light going through the scope is refracted.
6) Windage Adjustment
Shifts the aiming point of the scope on the horizontal (left/right) plane. Used to “sight in” your scope. Often measured as a “Minute of Angle” each ‘click’ of the knob you turn changes the aim point a certain amount at 100 yards. For example, a ¼ MOA changes the aim point ¼” left or right at 100 yards. A 1/8 MOA changes the aim point 1/8” left or right at 100 yards.
7) Elevation Adjustment
Shifts the aiming point of a rifle scope on the vertical (up/down) plane. Used to sight in your scope. Same MOA as windage adjustment applies only changes your aim point higher or lower.
Note: Some new scopes have the elevation dial graduated for a specific caliber of bullet (typically the .223). These scopes are meant to be sighted in at 100 yards. To take a 200 yard shot, you dial the elevation adjustment to "200" and keep the cross hair/reticle right on the target. No need to estimate hold-over.
Leupold (and perhaps others) will actually manufacture a special elevation knob for any caliber. You can call them with your ballistics and they will make the elevation dial. This special dial lets you set the distance of your shot so no hold-over is required. If you do a lot of long range shooting it may be worth the money to get a special dial made.
A rifle scope is really a tube inside a tube. The inner tube contains lenses to refract light while the outer tube protects the inner tube and provides a solid mount for the eye piece bell and objective bell.
Knowing the tube diameter is important because the rings that hold the scope to the mounts on your rifle are sized for different tube diameters. Most scopes made in the US have 1” diameter tubes, while most European and Japanese scopes have 30mm (slight bigger than 1”) diameter tubes.
Don’t try to tighten down 1” rings on a 30mm diameter tube because you can damage your scope!
9) Objective Bell
Housing the objective lens and the tube get attached to.
10) Objective lens
The lens that collects the light that goes through your scope. The diameter of the objective lens is very important. Generally, the higher the scope's magnification the larger the objective lens diameter must be to get the proper exit pupil (see below). For scopes up to 4-12x magnification, 40mm objective lens will work fine. A 50mm objective lens provides very little benefit in terms of light transmission with lower magnification scopes when compared to the extra cost, weight and higher mount height required for a 50mm lens.
Exit pupil is the diameter of the beam of light leaving the eyepiece. It’s usually measured in millimeters. A large exit pupil is advantageous under low light conditions and at night because the larger the exit pupil, the brighter the image (to a point). The exit pupil of the scope should be a least a large in diameter as the dilation of your eye's pupil. The human will dialate between 2mm in bright sunlight to 7mm in darkness. Maximum dilation tends to decrease with age. By age 50, the maximum exit pupil may be close to 5mm.
Note: if the exit pupil is larger than your pupils diameter, the sight picture will not look any brighter than it does when the exit pupil is the same as your eye's pupil.
To calculate the exit pupil, simply divide the diameter of the scope’s objective lens by the magnification the scope is set on.
For example, a 3-9x40mm scope has an exit pupil of 13mm at 3x and 4.4mm at 9x.
Assume you are a 50 year old and at first light of day your eyes are dialated to 5mm and you are using a 3-9x40mm scope. The maximum magnification you can use and still have the brightest possible sight picture would be at 40mm (scope objective)/5mm (your pupils diameter)= 8x magnification.
For a 50mm scope, that would be 50mm/5mm= 10x magnification.
This is important: You can see what a 50mm objective scope allows you to do is use a little more magnification in low light compared to a 40mm. IF you will not be using the higher end of your scope's magnification in low light, don't get a 50mm scope. Personally I do not own a 50mm scope becuase 8x is plenty of magnification for the type of hunting I do. Your situation may be different.
Adjustable Objective Lens (AO)
A rifle scope with an adjustable objective lens corrects a problem called parallax error (see below for explanation).
That’s the basics of scopes anatomy, what else should you consider?
Field of view (FOV)
This is simply what you see through the scope when you look through it. For a given power the wider the FOV you see the better.
Almost all rifle scopes provide some level of magnification. Some have a fixed power and the power is generally denoted like this: “4x”, meaning the scope enlarges the image by 4 times what you see with the naked eye.
A variable power scope will have nomenclature like this: “3-9x, 50mm”. This means the scope will magnify an image between 3 and 9 times, and every power in between. The 50mm means this scope has an objective lens with a 50mm diameter.
Having a variable power rifle scope is nice. It allows you to adjust the magnification to the situation you are in. If you hunt your morning sit near deer beds and its pretty thick cover, you can crank down the power. In the afternoon you might hunt a field, then you can crank up the power.
The down side to variable power scopes is they are more expensive than fixed power scopes and I have found the lower priced variable power scopes to require more frequent sighting in. I think the problem with the variable power scope losing its “zero” more easily than a fixed power scope is the fact that there’s moving parts in the scope. A good quality variable power scope will eliminate this problem.
All things being equal, if you can afford a variable power scope get one.
What power scope do I need?
That depends on what you are using your gun for. For hunting, if you limit your shots to 100 yards or less for big game you don’t need any more than 7x. For 100-200 yard shots 7x to 9x is good. Over 200 yards 9x to 12x is required. Here’s some guidelines:
Squirrels: up to 4x
Big game in dense woods: 1.5-4x or 2-7x
Big game in fairly open country: 3-9x or 2.5-10x
Big game in wide open country: 4-12x or 6-18x
For competition target shooting you really have to know the type of shooting you are going to do. Fixed vs. moving targets; pistol or rifle; large caliber or small. Consult someone who shoots targets the way you do and find out what power scope works for them.
The part of the rifle scope that references the center of the field of view (where you want the bullet to hit) is called the reticle. Years ago the “cross hair” was about all you could get, but today there’s a wide choice of reticles. The most popular is the Duplex, but there are others like the German #4, various post and dot reticles, and even illuminated (lighted) reticles. Some newer reticles are the Ballistic Mil Dot, BDC (Bullet Drop Compensator) and TRM (Tactical Milling Reticle) to name a few. These ballistic reticles have graduations on the cross hairs so you can adjust for the shot distance and for any wind very accurately.
Reticle choice can be more taste than science. Some better scopes are offered with a variety of reticles, so choose the one you feel most comfortable with. Note; Don't be intimidated by ballistic reticles. If you are a long range shooter you may find them to be real handy and they are not hard to use.
The cross hair (or other reticle type) is physically on one of the lenses on the inner tune of your scope. Most scopes are set to have the cross hair perfectly aligned with the target at 100-150 yards and the scope in perfect focus for that yardage.
When you shoot at a distance other than what your scope was factory set for a small error can be introduced if your eye is not perfectly centered in the scope. It is called parallax error. Lower powered scopes are less affected by parallax error than high power (12x or more) scopes.
For most hunting purposes it isn’t worth worrying about because the error is very small. For target shooters or long range hunting (over 500 yards) the solution to the parallax problem is to buy a scope with an adjustable objective lens or a side focus. You simply dial in the range you believe the target is from you and you are now parallax free at that range.
This is a measure of how much light coming into the objective lens actually exits the ocular lens. A rifle scope with quality optics will let almost all the light through the scope resulting in better low light shooting performance.
Some manufactures quote light transmission numbers like “95% resolution” or “95% light transmission”. While this may be true I don’t know if there’s a standard. Manufacturers of poor quality scopes brag about high light transmission numbers and I take that with a grain of salt. I tend to believe the numbers from the manufacturers of high quality scopes.
Resolution is how straight or 'coherent' the beam of light is that exits the scope. A scope with good resolution will have a 'sharp' sight picture. Scopes with poor resolution will have a sight picture that appears a little fuzzy.
Resolution is hard to measure but you know it when you see it. My NRA magazine tests scopes every month and they have devised a simple measure for resolution. They look at a chart with a series of lines that get progressively thinner. The thinner the line that can be seen, the better the resolution. It never fails that better quality scopes have better resolution by this meathod.
While manufactures of poor quality scopes can tout high light transmission numbers, you can't fake good resolution.
Almost all optics are coated with various materials to protect them from scratching, reduce glare and improve resolution. Make sure the scope you buy has coated lenses. Some manufactures claim to have advanced coatings that improve light transmission. I’m sure they help but to the average guy I don’t know how much difference it makes. If you tend to get shots in marginal light conditions then having advanced optics will benefit you.
You will want to use lens covers when storing your scope. No coating can protect the optics if spent shells are bouncing off them while you drive to and from the range or woods.
Sealed, water and fog proof
You should buy a scope that is well sealed. If moisture enters the scope it will “fog up”. Good quality rifles scopes can take a lot of abuse and not have the seal break.
Sighting in your scope
Some people call it sighting in your rifle, but you’re really sighting in your scope. Your rifle will shoot where ever it’s pointed, what you want is for the center of your scope's reticle to correspond to where your rifle shoots a bullet at a given range.
The distance you sight in is based on the type of gun you’re shooting and the distance you think you’re most likely to shoot at.
High powered rifles tend to shoot ‘flat’ trajectories, meaning the bullet doesn’t drop very much over distance. The most popular distance to sight in is 100 yards, but if you’re average shot is going to be 200 yards then sight in at 200.
Shotguns, pistols and muzzleloaders have less range than rifles, and therefore are typically sited in for 25-75 yards.
Bore sighting is a means of getting you scope close to being sighted in without shooting. The old fashioned way was to put the rifle in a gun vice and look down through the barrel and line it up with the bulls eye. Today there are magnetic boresighters and laser boresighters to help get you close before you start burning up expensive ammo. Keep in mind bore sighted is NOT sighted in. You have to shoot to make sure you’re zeroed in.
You get what you pay for
Rifle scopes are like most products you buy. You get what you pay for. You can’t expect a $100 scope to perform as good as a $400 scope. But there is a point of diminishing returns. Is a $1600 scope really 4 times better than a $400 scope? NO way. But, sometimes a little better makes a big difference depending on the type of shooting you are doing.
For the average hunter you can find good rifle scopes for $200-$800. You can shoot the rest of your life with a scope in this range and be very happy. If you are hunting game where real high magnification is required and the shots are 400 yards then you will require a higher degree of precision.
Target shooters and SWAT teams are a different story. Very small differences in scope quality can make a big difference in the desired result. Rifle scopes of this type costing a $1000 and up are not uncommon.
Choosing your scope
I hope this information has helped you. Knowing the type of shooting you are likely to do you should have an idea if you need a variable scope and the magnification required.
When it comes to quality, here’s a piece of advice: Decide on the quality of scope you need then buy a little better than that. You will never regret buying a little too good, but will always curse yourself for not buying good enough.