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Understanding Firearms Optics

Saturday, 16 March 2013 00:00 Written by 

There are a lot of firearm optics on the market designed to help shooters get a bullet from point A to point B with the maximum amount of accuracy. Some are great, some are good, and some are just plain junk with no other purpose than to separate folks from their hard earned cash. Open any firearms accessory related catalog to the optics section, and your senses can be quickly overwhelmed by the number of optic devices, the shapes, sizes, technical descriptions, and of course, prices. It can get a little intimidating, especially for the novice optics buyer. So, let’s take a look at optics, and their accessories, to remove some of that intimidation.

Demystifying Scopes

What could be more simple than buying a metal tube containing a magnifying glass lens on each end, and a means of aiming it installed somewhere inside the middle? One would then assume after mounting it to their firearm, all you need to do is line the target up in the crosshairs and shazam… you’re a world class sniper!!!  Ah, if only it were that simple.

Before you slip your shoes on and head out the door to go scope shopping, or plop down in front of your computer, there are a number of things you need to know in advance. You see, not all scopes are created equal. For example; do you want a scope with a fixed focal power or a variable (adjustable) focal power? How large of an objective lens do you want? What type of reticle (crosshairs) will fit your needs? How much “eye relief” (distance from eye to focal lens) will you require?  What interior diameter size scope rings will you need to fit the scope tube, and what height rings will you need to insure the objective lens sits the proper height above the barrel? Perhaps the absolute first thing you’ll need to know is; how much do you have to invest in a scope?

I know we have only just begun, but are your eyes starting to get that bleeding feeling yet?

Fixed And Variable Focal Power Scopes

A fixed focal power scope is one that has a set magnification; such as 4 X (or 4 times) larger target size than what you would see with the unaided eye. The higher the number, the closer the target appears.

A variable focal power scope allows the user to dial the scope power from a set minimum to a set maximum. An example would be 4 to 12 X or, adjustable from 4 up to 12 times the magnification of the target as seen with the unaided eye.

When talking about scopes, a fixed focal power scope would be referred to by its focal power number; such as a “4 by” or a “4 power scope,” a 6 by or 6 power scope and so on.

When talking about variable power scopes, with (for example) a 3 to 9 power range, one would say just that, “3 to 9 power.”

I should explain that variable power scopes do have a drawback. At close ranges, turning the power dial up brings the target in a lot closer; perhaps close enough to count the number of holes in a shirt button, but maybe too close to be able to see the arms of the shirt. To be blunt, you might not have enough field of view to see what the hands sticking out of those shirt arms are doing. 

The “field of view” refers to how much area the scope allows you to view at a given distance; usually 100 yards. Field of view varies by scope models and magnification power.

Another detriment of using high power settings at close distances is; normal minor movement of an unsupported firearm will also be magnified (multiplied). In other words, if you are aiming at a button sized target and your crosshairs appear to be moving around within a couple of inches of dead center of the button, due to wavering, at the moment the trigger is squeezed the bullet miss outside of the button’s diameter will be multiplied several times. Therefore, it is totally possible to miss a human sized target at those close ranges. Always follow the old adage “aim small, miss small.”

Objective Lens Sizes

When looking through a scope, your eye is nearest the “focal lens” and the “objective lens” is on the other end of the scope. The diameter of the objective lens is measured in millimeters. The larger the objective lens, the more light that is allowed to enter the scope and therefore, the better the viewing quality. Typically, objective lens diameters run between 20 and 50mm. Of course, the larger the lenses, the more the scope will weigh.    

In common scope nomenclature, a variable power scope with a 3 to 12 power and a 40mm objective lens will be referred to as a 3 to 12 by 40 variable scope.


A reticle is the aiming device you see when looking through a scope. A reticle could be nothing more than standard crosshairs, a dot, circles, or pointed posts that, once adjusted to your firearm and particular ammunition, assist you in putting a bullet where you want it to go.

Leupold Optics

Years ago, crosshairs were the most common type of reticle and they consisted of two very fine wires that formed a cross. Today, most reticles are marks that are etched into two pieces of glass. One piece moves up and down while the other moves side to side. Moving the reticle is how you move the point of impact of the bullet.

A more recent improvement to reticles is the projecting of a small light source on them, causing the reticle to glow, typically red or green, and thus providing for a better target acquisition in low light situations.  

There are two drawbacks to these lighted reticles; (1) they require a battery and (2) when set at the brightest settings, the interior of the scope will emit just enough light to be noticed by folks on the wrong end of the scope.

When shopping for scopes online, the better catalogs will usually show a drawing depicting the type of reticle for each scope listed.

Eye Relief

Not all rifles fit all shooters. Sometimes, the rifle stock is too long or too short for a particular shooter’s body size and this will put the scope’s focal lens at a distance that is too close or too far from the shooter’s eye. This is usually apparent when looking through a scope and a portion of the target appears blacked out as opposed to the target picture filling the entire diameter of the scope lens. Usually, this can be corrected by moving the scope a little forward or rearward in the scope mounting rings. Though eye relief distances vary between scope manufacturers, it usually ranges between 3” and 4.5”.

Scope Rings

Scopes need a means of being mounted to a firearm and that is where scope rings come into play. But certain firearms require different methods of mounting the rings to the weapon. Some use a Weaver type mounting rail while others use a Picatinny rail. Some require a mounting base that must have holes drilled and tapped into the weapon receiver. Rifles made by Ruger Firearms have a proprietary mounting setup that requires the use of Ruger manufactured rings.

Once the mounting method of the rings is determined, you then need to know the external diameter of the scope tube in order to obtain the rings with the correct interior diameter for that particular scope tube. They typically are manufactured in either 30 millimeter or 1 inch diameters.

Lastly, you have to determine the correct height of the rings for the scope you decide upon. Optimally, you want the bottom of the objective lens as close to the top of the barrel, without it actually touching the barrel. So the bigger the objective lens diameter, the higher the rings. Generally, there are four scope ring heights; low, medium, high and extra high.

Some models of scope rings mount tight to the weapon’s receiver and require at least a screw driver for removal. Others have a “quick release” lever device for mounting. Either method is more than an acceptable means of mounting a scope or scope like sight to your weapon.

Scope Costs

You can find scopes ranging in price from under twenty dollars to well over a thousand dollars. And of course, price makes all the difference in the world. If you go cheap, you risk very poor quality lenses that show a lot of viewing distortion. The scope bodies may not seal well, allowing for internal fogging problems during temperature changes. The reticles may be poorly made or poorly mounted inside the scope body and therefore subject to settings being lost after each shot, or damaged beyond repair by the vibrations when the weapon is fired.

My best advice when buying a scope is; do your homework. Research a variety of scopes from different sources and always read the customer reviews for each one. Some of the chain stores (Bass Pro Shops, Cabela’s and Gander Mountain) often have displays with different scopes mounted on dummy stocks so that you can “shoulder” the scopes rather than merely holding them in an unsteady one or two hand grip while trying to look through them. This is definitely a step or two up from buying sight untouched over the internet.

Night Vision Scopes

A truly tactical marvel of engineering, night vision weapon scopes are great when you are likely to be doing some shooting in very low to no light level situations.

Night vision scopes (or NVS) rely on a electronic powered light intensifier diode to gather light from the most minute sources (moon, stars, or infrared emitters) to produce a green / white projection inside the viewing portion of the scope. They include a lighted reticle, usually with a separate power switch, allowing the scope to be used as a weapon scope or, used to survey an area much like a night vision camera, without the inconvenience of having the reticle obscure one’s vision.

The downside to NVS systems is; they require batteries and can go through batteries fairly quickly. They tend to go through batteries even faster when the reticle is turned on. Also, they do add some weight to a rifle. Older generation NVS can weigh in at a couple of pounds. Lastly, it is important to have the objective lens cover on when in lighted areas and particularly to shield out direct sunlight as this can “burn out” the light intensifier module. Current generation NVS tend to be quite expensive while the older, first gen models and cheesy made units can be had for around five hundred dollars.

Red Dot Sights

Although frequently called scopes, red dot sights are not actually scopes, although some models are scope like in appearance. Red dot sights don’t have the highly polished glass lenses that true scopes have. For the most part, the majority of red dot sights don’t even sport magnifying lenses and those that do generally have only a 1X magnification power factor. Others receive magnification by way of an add-on accessory that is either mounted onto the focal lens or mounted in line with the sight and to the weapon’s receiver.

Red dot sights operate much the same way as lighted reticle scopes.  A small light emitting diode (LED) is mounted near the front of the sight body and aimed forward. The LED projects the light source that is then reflected off the back of a specially coated front lens. Adjusting the LED up, down or side to side moves the projected “dot” dot of light on the lens thus changing the impact point of the bullet on the target.

The upside of red dot sights is; they provide for a very fast target acquisition at nearly all distances out to about 200 yards. They are relatively inexpensive.

The downside is; they run off batteries and the cheaper made units are easily knocked out of adjustment by minor impacts or vibrations from firing the weapon.   

Red dot sights also come in green dot models or, in some cases, both red and green. Mounting options vary and the models that have scope type bodies generally need only one scope ring rather than two.

Scope Accessories

There are numerous accessories for scopes but none as important as lens covers. These covers protect your lenses from scratches and in some cases, external fogging. They’re cheap yet outstanding insurance.

Some models of scope covers are held in place by elastic cords (bikini scope covers) while others are a press fit to the housing around the focal and objective lenses. Some have to be “popped up” in order to look through the scope while others are see-through.

I would also recommend a padded scope cover to protect the scope while on the weapon but not in use. As the name implies, scope covers are like a jacket that surrounds the scope and attaches by either Velcro, elastic cords or straps with buckles. Padded models help buffer the scope from minor impacts that might throw the reticles out of alignment and they help prevent accidental scratches to lenses.

Some Personal Advice

If you are planning to purchase a rifle and scope at the same time, do not assume that having a scope negates the need for having regular sights (iron sights) already included on the rifle. Yes, many models of rifles are sold without sights. If some catastrophic damage befalls your scope at the worst possible of times, how will you aim your rifle with any amount of accuracy?

In Conclusion

I hope I have provided you with adequate information to make an informed decision when buying firearm scopes or sight devices. Understanding the basics will help to make scope buying a lot less intimidating, not to mention help guide you away from bad advice from those who are mentally “optics challenged.” 

Last modified on Tuesday, 09 April 2013 22:21
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