Understanding Scopes

Before any consideration of how much money to spend on an optic I feel we should first consider both the nature of use, and the environment the weapon will be used in and what kind of weapon the customer wants to use the scope on. Presuming he or she has made a decision to mount a scope on a rifle or a pistol, we should also be considering if the purpose is for fun and casual plinking, small game hunting, for competition at events such as the 1 mile milk bottle shoot, or a life or death use scenarion where someone with very similar (or even more deadly) equipment is trying their best to kill them first.

Answering those questions will very much impact how deep into their wallet a shooter should dip. If I am 40 yard plinking at nerf balls in a back yard or scampering ground hogs with a Nylon 66 it will probably have a vintage Weaver V22A (1960s & 1970s, less than $20) or a contemporary cheap Tasco from Walmart for $30.

Scoped pistols require a much longer eye relief as the pistol is held out at arms reach. Scoped pistols are usually intended to put meat on the table and one should spend a little more money than the ones for the .22 rimfire intended for casual plinking..

If a customer is going to be doing long range precision shooting they should be prepared to shell out much more money than they would pay for a less capable scope. The Vortex Razor HD Gen II 4.5-27×56 sells for $2,298.99 today, while a Leupold Mark 4 ER/T 6.5-20x50mm (30mm) M5 Front Focal TMR Rifle Scope sells for $1,429 today (prices from Amazon). Other long range precision shooting scopes have similar prices.

A shoter of an AR using a red dot type sight for close range shooting may find their scope needs met for dealing with occasional distant targets by using a simple quick detachable flip mount magnifier placed behind the red dot sight. For close shooting the scope sits in a flipped to the side position so it does not interfere. Should circumstances such as a shot at distance require magnification the scope is simply flipped into an upright position nnd the image in the red dot is magnified.

Once the shooter has determined the type of shooting they will be doing and the terrain there are many other variables to consider when choosing a scope.

The objective lens size determines the amount of light gathered and the field of view size. Larger objective lenses provide more light but also add size and bulk. If the shooter is going to be carrying the rifle then this is something they want to think about. But if they will be shooting from a fized position such as a shooting table or with a bipod that might not matter much.

The diameter of the tube, 1 inch (aka 26mm) or 30mm? A 30mm tube allows sturdier construction and the use of larger lenses. Additionally a 30mm tube can allow for up 20 MOA additional reticle adjustment. For a long range shooter that can be very important.

Which reticle is best for the intended use? A range finding reticle may be best for someone anticipating shots at a variety of ranges. However a long range precision shooter doesn’t need that feature as those matches are often fired at known ranges (i.e., 1,000 yards, 1,500 yards, etc.) and a simple cross hair or dot may be the most practical for that application.

Scopes with built in laser range finders now exist. Scopes capable of making their own video recording of a shooting event for review later also now exist. Both options require batteries.

Windage and elevation turrets. Hunters may wish a scope with turrets that are covered with turret caps and which are only adjusted while sighting the rifle in before a hunt begins and thereafter left alone, but a target shooter firing at long ranges of 800 yards or more may want a turret with quickly adjustble turret rings in order to cope with changing wind velocity and other factors.

It should be remembered that as magnification increases the light reaching the shooter is reduced and that the field of view is also decreased. Some of the higher magnifications are almost useless in normal hunting conditions. Variable scopes add weight and complexity to the scope. Both the range and the target size should be considered when selecting the desired magnification. A small target such as a rabbits head may need a high magnification, while a larger target such as a moose at the same range may require less magnification. Firearms intended for use hunting at closer ranges, i.e., under 100 yards are often best when equipped with scopes of not more than 6 power. A variable power scope is often not needed for such an application.

The amount of light reaching the eye of the shooter is a function of the size of the front objectixe lens and the magnification of the scope. Large objective lenses admit more light, but they also require the scope be mounted higher up on the rifle. Ideally the shooter’s line of sight should be as close to the rifle’s bore line as possible. The pupil of a human eye changes in size depending on how much light is available. The pupil size may vary from 2mm in bright light up to 7mm as the pupil enlarges to admit more light in hours of darkness.4 The goal of a scope is to ensure that the shooter’s pupil receives at least as much light as it would if the scope was not present.

[electronic Night Vision scopes that amplify such as a PVS 5 or a PVS 14 or the Russian IPN series are a seperate topic.]

The formula for calculating a scopes exit pupil size is the objective lens size divided by the magnification. Using the early Aimsport 3 – 9 x 32 scope mentioned earlier we see that in low light conditions at a magnification setting of 9 power the exit pupil of the scope is only 3.55mm at a time when the shooter’s pupil may be 5 or more millimeters in diameter. This would be an image so dark as to be almost useless. Conversely, in daylight at 3 power magnification the scopes exit pupil would be 10.6mm which would present as much light as if the scope were not present. In daylight hours the setting of 9 ower magnification would be entirely adequate.

In point of fact for a 9 power magnification to provide an exit pupil size of 7mm right after sundown (twilight) then the scopes objective lens size would have to be 63mm. This would sit farily high above the line of the barrel and probably be heavy and unbalanced as well. The long range precision scope by Vortex-Optics mentioned above has an objective lens of 56mm.

Long range shooters may also want a level built in or attached to their scope to ensure the scope is not canted as canting a scope may cause errors to the left or right of the center line as elevation is adjusted.

Ruggedness and durability is another factor to be considered. A light weight scope designed for use on a .22LR rifle would probably break under the recoil forces generated by a .300 Winchester Magnum or a more powerful cartridge. Shooters who anticipate using their scope under adverse conditions may wish to consider a scope built to military ruggedness standards with a rubberized exterior. Scopes rugged enough to take the recoil of a .300 Winchester Magnum may be overly heavy and bulky for use on a light .22LR rifle.

Lens coatings to aid in optical clarity exist as do special coatings to reduce the chance of sunlight reflecting off the scope glass. Lens hoods are another option to accomplish prevention of reflection.

A broad selection of price ranges exist for almost any kind of shooting and sometimes some of the lower priced models will have features very similar to the higher priced models.

for your entertainment

Long Range Shooting Milk Jug at 1 Mile (1760 yards) – 3rd Shot Jim Miehl – Milk Jug Challenge.


Leave a Reply