Rangefinders

These are "time of flight" systems where the round trip propagation time is measured and divided by twice the propagation velocity.

The oldest optical system is based on the concept of stadia.  The idea is that you can determine distance by measuring the included angle of an object of known height.
Examples: K&E 76 0000 Alidade, Leitz 115A transit

Another system is based on the "split image" that's made to align by rotating a mirror.  The difference in angle between the two mirrors can be solved based on their separation into the range.  This is the method used by "rangefinder" cameras and the military rangefinders that look like a drain pipe as well is civilian rangefinders like the hand held
Edscorp Field Range Finder.

Image property range finders are used in modern digital cameras.  One way these work is to look at the image contrast as the lens is set a various focal lengths.  The highest contrast image is deemed to be the best focused.

Time of flight is used in modern digital optical range finders like the Busshnell golf binoculars and the Laser Technology Criterion units.  These typically have one lens for the outgoing pulse of IR light and a separate lens to focus the light on a fast photo sensor.

One objective lens is for the IR transmitter and the other is for the IR receiver.  There is a small visual telescope in the center that's for the operator to observe where the spot is pointing.  The two large lens are black in color, not clear like optical binoculars.  The range is displayed in units of either meters or yards, a little to coarse for surveying.