This is the first instalment in a 3 part series of rifle scope 101 articles. Through this series we will cover everything there is to know about rifle scopes including understanding the importance of spending on a quality rifle scope and what each part is and used for, mounting a scope, mechanical zero, lapping, bore-sighting, windage, elevation, MOA, point of aim and impact and parallax. Lets get started with the first of the bunch; understanding rifle scopes and their parts.

The Purchase of a Lifetime

I was told a long time ago by a dear friend and avid hunter that your optics should cost more than your rifle. That made absolutely no sense to me at the time. How can you spend 800.00 US Dollars on a Remington 700 and then spend more than that for something that doesn’t actually do anything but help you see better? As time went by and my experiences in hunting grew, I began to realize that he was right. I had purchased a used rifle with a questionable quality scope mounted on it and I just could not figure out why I never got any tight accurate grouping with that rifle. A scope is a scope as far as I was concerned. It’s the rifles fault or mine, that was my thought process. Many hours of frustration and hundreds of rounds later, I took the rifle to a gunsmith friend and he examined the rifle for me.

My gunsmith just shook his head at my rifle and scope combination and started lecturing me on the world of optical scopes. He explained to me my folly by taking the scope from my rifle and threw the scope into the garbage can. Of course, I dove into the garbage can after it. I guess I was too pitiful for him so he let me recover it. He just got down one of his rifles and started comparing the two scopes side by side. He knew that an actual side by side comparison is how some hard headed people need to be educated. After that day, my scopes always cost more than my rifle.

Like the old adage, you get what you pay for. By purchasing a poor quality scope, you are opening up the Pandora’s Box of frustration, annoyances and just plain disgust as you try and figure out what is the matter with you. You start becoming a poor shot, can’t maintain an accurate grouping and begin to wonder about your eyesight and sanity. I have been there, but this article will teach you what I learned so many years ago.

An optical scope is another tool in a hunter’s tool bag. As any good craftsman will tell you, you should know how to use every tool in your tool bag properly. Knowing each tools function and limitations makes a craftsman the artist they are. As a hunter, we are all craftsman. We have to master several skill sets, maintain and be proficient with firearms, learn about the animals we are hunting and hunt safely and economically. By purchasing a subpar rifle scope, you are adding a variable that will lead to frustration. By not knowing how optical scopes work, you are cheating yourself out of getting the best performance out of your scope and your rifle. The knowledge on how to properly use a rifle scope will make you a better hunter. Let’s start the journey.

Why Spend the Money At All

We see hunters today with a dizzying variety of optical scopes and red dot scopes mounted on rifles, crossbows, bows and even black powder. Using a scope makes the task of aiming and hitting a target extremely easy. Instead of having to line up the front iron sight with the rear iron sight and maintaining focus on the front sight while aiming at a target, all a scope user has to do is line up the crosshair reticle with their target.

Another added advantage is most scopes have magnification. Magnification allows the hunter to see the target better and allows for better shot placement. For people with less than perfect vision, using the adjustment at the ocular eyepiece allows them to adjust the reticle focus making for a crisper, clearer view through the scope.

Parts of a Whole

The various terminology used in describing scopes can be very confusing. It is important that you the hunter understands these terms and has a working knowledge on how scopes actually work. I am going to start at the front part of the scope (the part closest to the muzzle) and work my way back toward the shooters eye.

Objective Lens (objective glass or object lens)

The lens at the end of the rifle scope has no bearing on “magnification”. A lot of people seem to think the bigger the objective lens, the more “powerful” the scope is. That is incorrect. The objective lens is used to gather the image of the target and to allow light into the scope. The larger the objective size the more ambient light will be introduced into the scope to your eyepiece.

The objective lens has an objective bell which is the housing for the objective lens. Some of these bells can hold lens up to 75mm or more. This actually can be a detriment because the scope needs to be mounted higher and this causes neck strain, eye strain and an awkward stock weld. A good rule of thumb for how an objective lens works is the objective lens diameter divided by the magnification equals the diameter of the exit pupil. So a standard 40m objective lens at 5x power will give you an 8mm exit pupil or the image on the ocular lens.

Scope Tube (barrel or main tube)

The most common scope tube sizes are 1 inch and 30mm. The diameter is measured by the size of the main tube between the adjustment turrets and the objective bell and the diameter from the turrets to the eyepiece or magnification ring.

There is a lot of discussion on which is better, 1 inch or 30mm. The 1 inch scope is usually lighter, has a thinner barrel and has less internal adjustment for the ‘crosshair’ or aiming reticle. A 30mm barrel is usually thicker, heavier but has more room for adjustment of the ‘crosshair’. This makes the 30mm tube better suited for long range shooting and hunting. This makes neither the 1 inch nor 30mm ‘better’ than the other. If you are planning on taking long range shots in a harsh environment the purchase of a 30mm scope might be to your advantage but a lot of people use 1 inch tubes with success.

The use of a 30mm tube for better light transmission will give you a very slight increase, if any. You can get good light transmission with good quality optic components and objective lens size. If you routinely take shots past 500 yards, a 30mm tube should give you more internal reticle adjustment but you can purchase a scope base that can add more MOA to your adjustment range if you use a 1 inch scope. The choice between a 30mm tube and a 1 inch tube is more a personal preference than a written in stone, ‘this one is better’ fact.

External Adjustment Turrets (turret housing, windage and elevation adjustment)

The three most common adjustments for any rifle scope are windage, elevation and parralax. Keep reading as these three things will be discussed further down. It is very important that you read the instructions on how to adjust the point of impact. There are a multitude of methods used to adjust these three things.

Every company is different and even the age of the scope can have a bearing. Some companies require you to remove a protective cap to access the external adjustment, others have a ‘pull to turn’ feature. Be sure to see if they are sealed with an “O” ring to prevent moisture and debris from entering the scope. Some scopes have positive ‘clicks’ while others do not. The taller turrets in some scopes can be knocked around or snag in thick brush, that is why most hunting scopes have a lower profile turret.

Magnification Power Ring (power adjustment ring, zoom ring)

If your scope is a fixed power scope, this will be omitted. A fixed power scope has one set magnification power. In the olden days, this was preferred because the more moving parts the more wear and ‘slop’ could occur inside the scope. A lot of older military scopes were fixed power to ensure constant shot placement. A fixed power scope does hold some advantages. The hunter knows how much magnification they have, there is no fiddling with magnification during a shot and it is one less thing to worry about.

Your hunting partner calls you and tells you that he just bought a 3x-9x by 40mm scope. You make impressed noises over the phone but do you understand what that means? 3x is 3 times magnification making a target seem 3 times closer. 9x is 9 times magnification making a target seem 9 times as close. This scope has an adjustable magnification from 3 power to 9 power. This scope has variable power magnification. The 40mm is the objective lens size. A variable power scope allows the hunter to use a low magnification for close in shots and a higher power for longer range shots.

A variable power scope has a few advantages. If the hunter is in thick brush, they adjust the power down to the lowest setting. This will allow them to take a close range shot. If the power is too high, all they will see through the scope is a patch of fur since the deer is close but you have it set at 9 times magnification. A lower power will keep your field of view through the scope low so you can see more of the area. A lower power setting in dim light is best since it will allow more ambient light to go through the objective lens and out the exit pupil. The higher the magnification the less light you allow through the eyepiece.

Eyepiece

The eyepiece is not the same as the exit pupil. The eyepiece holds the ocular lens just like the objective bell holds the objective lens. The eyepiece might be adjustable for reticle focus for less than perfect eyes. Most eyepieces rotate in either direction to adjust the eyepieces lens in relation to the rifles reticle crosshairs.

Point the scope toward the sky (NOT THE SUN) or some other light colored field. If the view is not clear, remove the scope from your view and adjust the eyepiece ¼ turn in one direction or the other. Repeat this process, realizing that if it gets worse you rotate the eyepiece in the opposite direction gradually. The reticle should be clear and sharp. Do not attempt to focus by constantly looking through the eyepiece. Your eye will adjust to focus on the crosshair reticle after a few moments. Focus on the crosshair reticle, not the target.

Exit Pupil

The small circle of light that you see as you look through a scope at arms distance is called the exit pupil.

For example, take a rifle scope, set it at the lowest power available and hold it out at arm’s length. The circle of light visible through the ocular lens is the exit pupil. The diameter in millimeters is the exit pupil size we discussed with the formula objective lens diameter divided by the magnification equals the diameter of the exit pupil. So a 55mm objective lens with 5x power magnification will show you an 11mm exit pupil.

Now turn the variable scope power all the way up. Look through the eyepiece and you should notice that the exit pupil is a lot smaller. Try to imagine if you are now using that scope in a low light situation and have the power at maximum. That exit pupil will be dark and small, almost too small to use.

I hope I have given you something to think about when you are looking to purchase that new scope. When you are looking at variable power scopes, do the math to find out the largest and smallest exit pupil for that scope. For example, a 2x-6x by 30mm scope will give you at 2x power a 15mm exit pupil (30 divided by 2 equals 15mm exit pupil). At 6x power a 5mm exit pupil (30 divided by 6 equals 5mm exit pupil). A very large difference in available light from the exit pupil don’t you think?

What is so important about the exit pupil? The larger the exit pupil in size the less critical head placement is. The distance from the shooters eye to the ocular lens with the exit pupil projected on it is called eye relief. The distance from your eye to the ocular lens in a low power setting allows for greater range of distance but the higher the magnification power the more critical your eye is to be exactly centered on the scope. At maximum magnification, your eye has to be more exactly centered on the scope to ensure a complete and clear image.

Eye Relief

The longest eye relief for an optical rifle scope is about 4 inches. This leaves enough room for the rifle to recoil and not strike you, if you have the proper ring mounts and a cheek pad or raised cheek stock if needed. The higher the recoil of the rifle, the larger the eye relief needed to avoid ‘scope bite’, that painful and embarrassing cut above your shooting eye.

To avoid scope bite, it’s important to remember that you need to recoil as the rifle recoils. Scope bite is caused because your reflexes are not as fast as a recoiling rifle. You can NOT get your head out of the way; you have to have a positive stock cheek weld to ensure proper recoil survival. Remember that the further the eye relief is from the ocular lens the more loss of field of view through the scope.

There are a few other types of scopes available for different applications.

One type of rifle scope is called an Intermediate Eye Relief or IER scopes. These are more commonly referred to as a ‘Scout scope’. These scopes are mounted near the front of the rifle, or on the barrel and require a longer eye relief, sometimes 9 to 12 inches. These scopes allow for a larger field of view with both eyes open to acquire the target faster. They are usually fixed magnification power for fast action shooting.

For handguns, there is a type of scope called Long Eye Relief or LER scopes. These scopes are designed for pistol shooting and have a 15-20 inch eye relief. They are designed for both eye open shooting, having a lower fixed magnification power to allow for easier eye pupil viewing.

Putting a Coat on Your Scope

A good quality scope should be water resistant, shock proof and fog proof. A large selling point is coating on the optical lens. The optical coating on lens will maximize light transmission into the optics, reduce the loss of light due to reflection, add some scratch resistance and reduce glare. There are several levels of coating.

• Coated: There is at least one layer of protection on at least one lens surface. This can mean that only one lens has a coat.
• Fully coated: The scope will have a single layer on all air to glass lens.
• Multicoated: The scope will have a single layer on all air to glass lens with multiple coats on at least one lens.
• Fully multicoated: This scope will have multiple layers of coating on all air to glass lens.

The purchase of a scope cover to protect the mounted scope is a great idea. We all know the misadventures in hunting that can and will occur and its best to protect your investment. There are also lens covers that protect the lenses when not in use. Just a small investment of money can increase your scopes survivability.

Now that we have covered the importance of quality scopes and what each part means it’s time to graduate to mounting the scope.

Click Here to continue to Part 2: Mounting a Rifle Scope

or you can skip and go straight to Part 3

Click Here to skip to Part 3: Windage, Elevation & Parallax Adjustment

Image by jarmoluk, Markgraf-Ave, betancourt