Binoculars have 2 numbers, such as 8 x 25. The first number lets you know the magnification that the binoculars have. The second number will denote the diameter of the lens ( that is the one furthest away from your eye) in millimetres.
Anyone looking for compact binoculars will use these numbers to find the right pair of binoculars. The bigger the lens, then more light will be allowed in the binoculars giving a sharper and brighter image.
So larger objective lenses are much better in low light such as evening light. Rubber armoured binoculars absorb bumps. they provide extra grip and do not mark easy.