Handheld telescopic rod sight glass and use method

A handheld telescopic rod sight glass comprises a holding part, a connecting mechanism and a telescopic rod. The telescopic rod comprises a hard telescopic rod, a soft telescopic rod and a probe; the soft telescopic rod comprises a chain link assembly; each chain link assembly comprises a plurality of chain link units which are rotationally connected front and back, cable guide channels are formed in the centers of the chain link units, soft telescopic rod walls are arranged on the outer sides of the chain link units, bead-shaped heads are arranged at one ends of the chain link units, bead-shaped holes capable of being matched with the bead-shaped heads in an inserted mode are formed in the other ends of the chain link units, and disc springs are arranged on the two sides of each bead-shaped head in a mirror image mode. The disc spring is fixedly connected with an arch-shaped clamping plate, arch-shaped holes capable of being matched with the arch-shaped clamping plate in an inserted mode are formed in the tw