Abstract: A connecting device for connecting to a focusing lens or an aiming lens includes a frame detachably connected to an external device and including an installing member for fixing with a lens, and a fastening member for connecting the frame with the external device. The fastening member includes at least one group of wedge-shaped pair members engaged with each other and an adjusting device for driving two components with the at least one group of wedge-shaped pair members to slide relatively to the external device so that the frame can be tightly fixed with the external device. The frame can be tightly and reliably fixed with a guiding slider via the wedge-shaped pair member when they are locked to each other, and the adjusting device is provided for conveniently adjusting or locking the frame and the guiding slider so that the installation or disassembly of the frame can be conveniently obtained.