- Created on Saturday, 23 October 2010 00:03
- Last Updated on Tuesday, 18 September 2012 23:59
- Written by ILya Koshkin
Introduction: What is a Riflescope?
This may sound like a silly question, but bear with me. There is a method to my madness.
To a shooter, it is a weapon sight. It is supposed to be slapped on top of a weapon, sighted in and used for its intended purpose: aiming.
To an engineer, it is an opto-mechanical device that is used for aiming. Nowadays, it is not even always a pure opto-mechanical device since quite a few riflescopes have some electronics in them (reticle illumination, for example).
The distinction is important: to a shooter, this is just a means to an end. To an engineer, there are a lot more details to it, and the "means to an end" may be something else entirely.
An engineer tasked with designing a riflescope should have a pretty clear idea what it will be used for and what kind of abuse it is likely to be subjected to. He has to design it to withstand all reasonable (and sometimes unreasonable) abuse, while staying within other design requirements pertaining to size, weight, optical performance and, last but not least, budget. This last requirement is the reason behind most compromises made in riflescope design.
A shooter trying to select the right scope often ends up considering very different factors. Typically, he will have an idea of how much he wants to spend and a rough idea of what the overall configuration should be. However, all too often, a shooter is blissfully unaware of the challenges that an engineer faces in designing riflescopes. That is not necessarily a bad thing, since getting into the nitty-gritty of technical details is often counterproductive. However, some basic knowledge of riflescope construction is very useful, especially if you are looking for a scope on a budget. If you have unlimited funds and can drop somewhere in the neighborhood of $3k or thereabouts on a riflescope, you are paying for not having to worry about any of that. For that much money, it better be bloody perfect! For the rest of us, a little consideration goes a long way.
Before we dig into the details of how scopes work and how to select them, it is important to clearly define how much you can spend and what you need out of it. Here are a few questions that need to be answered before you get any firther:
What is your budget? How much are you willing to spend (keep in mind that you also need good quality rings and bases)?
What will be the basic application for the scope? Hunting? Target shooting? SHTF? Law Enforcement? etc.
What are the extremes of the lighting conditions you are likely to run into? Is low light performance critical?
What are the weight limitations? Is this going onto an ultra-light rifle that you plan to drag all over some distant mountains with you, all the while cursing every extra ounce you have strapped to your back? Or are you mounting this scope on top of a fifteen pound varmint rifle that gets moved twice a day on a good day?
What is the likely target size? You do not need much magnification to aim at something the size of a grizzly bear. However, aiming at a prairie dog barely sticking out of the ground is an entirely different story.
How far do you plan to shoot? If you plan to shoot at extended ranges, you will have to decide whether you want to dial in your point of aim using turrets or use a holdover reticle of some sort
What are the likely weather conditions you'll face? If you live in a climate where mirage can be a factor, you need to take that into account. Similarly, unusually wet climate creates its own set of problems.
How much recoil will the riflescope (and the shooter) be subjected to?
All of these questions are important in picking the right scope and, most importantly, picking a high quality scope for the right price.
Today, there are high quality riflescopes manufactured all over the world: Germany, Austria, Romania, Czech Republic, Japan, Phillipines, Korea and China. There are also quite a few "less than worthwhile" scopes out there, most of them manufactured in China. Price ranges from $20 scopes that might as well be disposable to $5000 Hensoldts that are as near to a family heirloom as scopes get.
The sheer number of different riflescopes available in the market place today is staggering. Some are "me too" products, while others are true innovations. Some are narrowly focused on one particular application, while others are designed to be allrounders.
On top of all that, innovative designs of just a few of years ago, look like perfectly ordinary items today. However, the basics of rifle scope design and construction do not change much, so the subsequent sections hold equally true to virtually all riflescope regardless of when they were manufactures. Any specific scope recommendations, on the other hand, need to be re-evaluated with reasonable regularity.
Configurations: what do all those numbers mean and which one is right for you?
Picture 1. Hawke Sidewinder 30 Tactical 4.5-14x40
Picture 2. Redfield Revolution 3-9x40The two pictures above show two very different scopes. The first one is intended as a mid-long range tactical scope, and the second one is an allround hunting scope. The basic anatomy of both scopes is about the same though:
- the flared front of the scope that is hanging over the back of the barrel is the "objective bell", with the front element often referred to as the objective lens
- the other, also flared, end that is over the open bolt in both pictures is the eyepiece
- the middle (cylindrical) part of the scope between the eyepiece and the objective is the maintube
- right around the center of the maintube are the adjustment turrets often referred to as "knobs". In picture 1 above, there are three turrets: elevation adjustment (top of the tube), windage adjustment (on the right of the tube) and a combination turret that controls reticle illumination and image focus (on the left of the tube). In picture 2, there are only two turrets: elevation and windage adjustments. Those adjustments physically move the reticle inside the scope, so that you can change where the scope is pointing (i.e. tweak it to point to the same spot as the rifle barrel)
- just in front of the eyepiece is the magnification ring; you rotate it to change magnification
Just to be thorough: 3-9x40 means that this is a variable magnification scope with a 40mm objective lens and with magnification ranging from 3x on the low end to 9x on the high end. Similarly, the 4.5-14x42 scope has a 42mm objective lens diameter and magnification range from 4.5x to 14x. Magnification range is often described by the "zoom ratio" or "erector ratio". For example, in a 3-9x40 scope the zoom ratio is 3x, other common zoom ratios are 4x, 5x and 6x, although there are now scopes with even larger magnification ranges.
Naturally, not all scopes have variable magnification. While they are not as popular as they used to be, quite a few riflescopes out there have fixed magnification. The most popular configurations of this type are 4x32, 6x42 and 10x42, although there are others.
As far as other specs go, first, there are the obvious ones: overall length and weight.
Then there is the maintube diameter. There is a number of different maintube diameters out there. The most common ones are 1 inch (25.5mm) and 30mm (in the pictures above, the somewhat larger scope is 30mm). However, there are also 7/8 inch, 26mm, 34mm, 35mm and 40mm scopes. I am sure that someone out there has made, at one time or another, scopes of other diameters. A natural question here is why are there so many different diameters out there? Most of the differences are simply due to historical reasons: different standards arose in different parts of the world. However, for some more complicated designs it helps to have a little more space inside the tube. For example, most scopes with higher erector ratios are built on 30mm or larger tubes.
Additionally, if the scope has a large objective bell, it creates a lot of inertia when the rifle moves under recoil. While we are used to think of recoil mostly going backwards, because the should typically contacts the buttstock below the centerline of the bore, there is also a considerable upward jolt. That upward jolt exerts a lot of force onto the scope. Slow motion videos of a rifle being fired have shown that the scope can bend significantly due to recoil. Since larger diameter tubes are stiffer (for the same wall thickness), they are better suited to supporting large objective lens systems. The downside of course is that larger tubes are heavier.