Rifle Scopes Glossary Of Terms
Descriptions of rifle scopes can be a little confusing at times, especially if you're new to scopes and shooting.
Here are the basics;
What does 4x20 mean?
- 4 - The first number means the magnification. In this example it is 4x (4 times) normal eyesight.
- 20 - means the diameter of the viewing lens (not the eyepiece) in millimeters. (the tech term for this is "Objective lens size"
- 4x20 - Therefore the scope is 4x magnification seen though a 20mm wide view lens.
And what about 3-9x40 then?
- This means the scope has variable "zoom" capability.
- In this case it ranges between 3 and 9x magnification though a 40mm wide view lens (objective lens)
- Unless otherwise stated the numbers are Whole numbers, so on a 3-9x there will be a 3, 4, 5, 6, 7, 8 and 9x position
but not fractions or some sort of granular 3.75x type of thing.
- 3-9xx40 is the most popular general purpose scope size. If you can afford one get one.
Time for the more Tech stuff now
Exit pupil: The size of the column of light that leaves the eyepiece of a scope.
- The larger the exit pupil, the brighter the image.
- To determine the size, divide the objective lens diameter by the power ( a 4x40 model has an exit pupil of 10mm)
This is why big mag scopes tend to have big lenses e.g. 8x56 and why you dont get 3-9x20,
Because basically they would be rubbish.
- The distance a scope can be held away from the eye and still present the full field of view.
- Unlike cartoons you don't have the eyepiece pressed up against your eye, if you did you are sure to get a black eye from recoil.
Field of View (F.O.V) : the side-to-side measurement of the circular viewing field or subject area.
- It is defined by the width in feet or meters of the area visible at 100 yards or meters.
- A wide field of view makes it easier to spot game and track moving targets.
- Generally, the higher the magnification, the narrower the field of view.
- Which is why variable magnification scopes are so handy. Spot the target at low mag and. Lock on and zoom in.
Windage & Elevation - The 2 turrets mid way down the scope body that are a key part of zeroing a scope.
When you fit a rifle scope they are up and to the right.
Windage - The one of the right
- As the name suggest it is to do with wind
- It adjusts the crosshair minutely left and right.
- And for in the field adjustments for wind strength where, for example a high crosswind will make long range shoots veer slightly.
- Again critical for getting zero and in the field where a strong head of tail wind effects a pellets lateral trajectory.
- A condition That occurs when the image of the target is not focused precisely on the reticule plane
- Parallax is visible as an apparent movement between the reticule and the target when the shooter moves his head or, in extreme cases, as an out of focus image.
- Some scores, higher priced ones typically, have parallax correction built in so that this focus problem does not occur.
That is it for this guide, will post more.
as i have just found pretty much all the documents that i was given from the NRA, even got a few army guides (Canadian army though) Which i will post on here at some point