Basic Information about Binoculars

This is the ratio of the apparent size of an object in comparison with what a viewer sees with the naked eye. For instance, an object 800m away viewed through 8x binoculars looks about equal in size to an object 100m away viewed with the naked eye. The higher the magnification, the more unstable the image will be due to hand movements. Higher magnification also results in a narrower field of view and lower brightness. Binoculars with magnifications up to 12x are recommended for general use. Also, using a tripod to prevent hand movements is highly recommended. Binoculars incorporating a VR (vibration reduction) function reduce image shake even at a high magnification.

Calculation of magnification:

  • Magnification= Effective objective diameter ÷ Exit pupil diameter
    = Focal length of objective lens ÷ Focal length of eyepiece lens

What is the relationship between the focal length of SLR cameras and the magnification of binoculars?

An interchangeable lens with 50mm focal length (in 35mm format) offers about 1x magnification. The effect of 8x binoculars is equivalent to that you can obtain by using a 400mm (50mm x 8 = 400mm) lens.