Optic Terms Explained


Binoculars have two eyepieces


Telescopes have one eyepiece

Ocular lens

The lens closest to the user’s eye

Objective lens

the end furthest from the user’s eye -the light-gathering lens


What does 10X50 to describe an optic mean?

What does 10X50 to describe an optic mean?
-The first number- here “10-” is the power of the magnification. The second number-here “50-” is the diameter of the objective lens in mm.



The basic rule of physics is “the more you magnify the more you narrow the view”. That rule applies to all optics.

Therefore a 35 X power telescope has more magnification than a 10X binocular but the telescope views a much smaller “patch of space” – a view with much less breadth.

If you have a scenic view you typically want the binocular view so you can take it all in.