Binoculars can be classified as either full-size or compact binoculars. The size of the objective lens affect how large or small a binocular is.

Full-Size Binoculars:
Full-size binoculars have at least 30mm of aperture or greater. They offer the light gathering ability needed to identify objects in low light conditions, however are not always as portable as one might desire.

Compact Binoculars:
Compact binoculars have less than 30mm of aperture, and are more portable than full-size models. However, due to their limited light gathering capability, they are best when ample light is available to the viewer.