Dear Customer, Thank you for your question. Please check the following steps to setting the focus: (Do not look at too close objects) Step 1. Cover the right objective lens with your hand or close your right eye, rotate the central independent focusing wheel until the image in the left eyepiece is sharp and clear. Step 2. Now cover the left objective lens or close your left eye, rotate the right eyepiece focusing wheel to adjust the diopter of the right eye until the captured image is sharp. 

For this binocular 20x50, as the diameter of the objective lens is 50mm, for binoculars, the larger the diameter of the objective lens, the more light it collects and therefore can be seen more clearly in dimmer places. Please note, however, that dim/low light ≠ night vision and cannot be used in total darkness. 

NO, dont listen to the other person who answered because they have no idea what they are talking about. these are 10x magnification. in one part of the listing is says 40mm is the size of the objective lens and in another part is says the objective lens is 60. either way it says in multiple spots that these are 10X magnification which makes sense because its identical to my expensive 10X binoculars 

This will work on any 82mm lens. 

This means that the magnification can be adjusted from 10 to 30 times, the objective lens is 50mm, a great telescope, light and durable.