Abstract: The invention aims at providing a pair of binoculars making it possible to easily perform a focusing operation and a diopter adjustment, and efficiently perform an assembling operation. The present invention provides a pair of binoculars having a pair of supporters for supporting adjustment lenses provided between a pair of ocular optical systems and a pair of objective optical systems so as to be capable of moving forward and backward along the optical axis, a focusing gear for performing a focusing operation by moving said pair of supporters forward or backward at the same time in the direction of optical axis, a diopter adjuster for performing a diopter adjustment by moving one supporter forward or backward in the direction of optical axis as keeping the other supporter stationary, and a focusing and diopter adjusting unit having a changeover gear for changing over the focusing gear and the diopter adjuster to each other.

Abstract: The invention relates to improving optical properties of optical instruments with variable magnification, such as zoom binoculars, reducing the weight thereof, and enabling the user to change magnifications quickly. The invention provides an optical instrument with a focal length-varying lens 4 disposed on the optical axis between an objective lens 7 and an eyepiece 3, further having an adjusting lens 5 for adjusting optical properties when the focal length-varying lens is in an area to provide high magnification. The adjusting lens is supported so that it is capable of moving between a location on the optical axis and a location off the path of light beams. Interlocked with a magnification-varying mechanism that controls the position of the focal length-varying lens, the adjusting lens is moved to the on-the-axis location when the focal length-varying lens is in an area to provide high magnification, and to the off-the-axis location when low magnification.