Front lens - Binoculars
The front lens is the lens located at the front of the objective. The diameter of the front lens is used to calculate the exit pupil, the twilight factor and the image brightness of the binoculars.
The size of the front lens determines how much light enters the binoculars. What consequently happens to all this light of course depends largely on the other features of the binoculars.
In high-quality binoculars, the front lens has a (multi)coating. The other lenses in the binoculars also have this coating. However, in the front lens, it is also important that the mechanical quality of the coating is in order. The coating must obviously be tough enough to withstand any bumps and jolts to avoid any damage to the lenses. However, it goes without saying that binoculars must be handled with great care at all times.