Eli5 : The numbers on binoculars


I recently used 10×40 binoculars. They weren’t powerful enough for me and I don’t fully understand those 10×40 numbers. I want something more powerful to see a bigger field of view. For wildlife, birds etc.

In: 2

10x is the magnification. 40 is the size of the objective lens in millimeters.

For a wider FOV, you need a larger lens (10xL). For higher magnification, you need, well, higher magnification (Mx40). For both, you need both (MxL). If you want variable magnification, that is also an option (M1-M2xL)

The first number is the magnification, the second number is the size of the objective (main) lens, in mm.

So a 10×40 magnifies things by a factor of 10 and the main lenses are 40mm across.

If you need more “power”, that usually means more magnification, but that would be a *narrower* field of view. If you want a wider field of view you need less magnification.

The size of the objective lenses is mostly about light gathering power (big lenses give you a brighter image, particularly in low light conditions), and also allow better detail.

The first number tells you how much bigger the image will be (magnification)… the second number tells you how big the lens is in millimeters, so yours make what you’re looking at 10x bigger with a 40mm lens…

Once you start to get bigger than that, it’ll be heavier and harder to hold still, so if you’re bird watching, I’d recommend looking into binoculars that have a tripod or mount for one

In your first example, 10 refers to the magnification being 10 times the actual size of the viewed object. The 40 is the diameter of the large lens at the front.

10 X 50 is usually the largest common size. It’s just about at the limit of what can be held steadily by hand. Anything bigger would almost certainly need a tripod or hide-clamp to be usable.

You might want to consider a small telescope.

10×40 means that everything looks 10 times bigger then without the binoculars and have a 50mm lens to collect light. You may also see a field of view label measured in how wide the image is at 1000m or a certain number of degrees. If you buy another 10×40 with a wider field of view the image will look the same but the dark ring limiting your vision will be wider so you can easier scan the landscape without having to move the binoculars. But you can also get a pair of 7×40 binoculars which will have improved field of view over your existing ones but not because the dark ring is larger but because you can see more things through it. This is like zooming out on a camera.