RIFLESCOPES - what do all those numbers mean and which one is right for me?

Discussion in 'Hunting' started by Webyshops.com, Sep 17, 2010.

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    Configurations: what do all those numbers mean and which one is right for you?

    Here are a couple of pictures of fairly typical riflescopes. I'll be referring to them periodically through the write-up. The first one is Hawke Sidewinder 30 Tactical 4.5-14x42:
    Picture 1. Hawke Sidewinder 30 Tactical 4.5-14x42

    The second one is Redfield Revolution 3-9x40:
    Picture 2. Redfield Revolution 3-9x40

    The 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 turrets that are 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
    • also, please note that on most scopes, the eyepiece contains some sort of a reticle focus adjustment. In picture 1 above, it is the so-called "fast-focus", which looks like a ring at the very back end of the eyepiece. In picture 2, the whole eye-piece rotates. Whichever type of the mechanism it is, the function is the same: to make the reticle look as sharp as possible. It is important to remember that the eyepiece focus is NOT for making the image as sharp as possible; it is for focusing the reticle ONLY.

    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. 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.


    Special thanks go to Ilya from OpticsThought.com for collaborating on this project.