The numbers on a rifle scope at first look confusing but they’re really very easy to understand. Let’s take an example.
3-9X40
The first number 3 means the minimum magnification level that the scope offers.Second number 9 the maximum magnification level.Because the first 2 numbers are a range separated by a hyphen we know this is a zoom scope.The 80mm after the X refers to the objective lens diameter in mm.
The numbers before the X always denote magnification power or power range and the numbers after the X denote the size of the objective lens in mm.
Here’s another example listing that looks slightly different:
4X32First number before the X means 4X magnification power or ‘4 power’ for short and the 32 means a 32mm objective lens. This scope is fixed, you can’t alter the magnification by zooming in or out. We know because the first number doesn’t specify a range.
If you ever see listings or specifications like this:
5X scope or 8X scope
The above is just shorthand for magnification power. 8X means 8 times magnification or ‘8 power’. This would be a fixed magnification scope. 8X is an image that’s 8 times bigger than what you see with the naked eye. Here’s an example of the effects of different magnification levels on an object.
Objective Lens Sizes
A larger objective lens will let in more light than a smaller lens. That makes for a brighter clearer image especially in low light conditions like dusk.
Rifle scopes have smaller objective lenses than binoculars. And binoculars generally have smaller lenses than spotting scopes. Each is designed for a different purpose.
A scope doesn’t need as big an objective lens as binoculars because you’re zoomed in on a single target, whereas spotting scopes need to allow as much light in as possible to allow you to see clearly at their high 60-80X magnification capabilities.