An apparatus comprising a range finder portion (16-18, 21-23, 61, 67, 71, 73, 77, 52, 57, 67, 68) that includes: a radiation generator configured to emit radiation having a selected wavelength; a radiation detector configured to detect radiation having said selected wavelength; an optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) which includes a non-reciprocal optical part, said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) being configured to route radiation emitted by said radiation generator at said selected wavelength through said non-reciprocal optical part and then through a single aperture toward a location remote from said apparatus, and to route radiation received through said single aperture at said selected wavelength through said non-reciprocal optical part and then to said radiation detector; and a further generator configured to emit radiation at a further wavelength different from said selected wavelength; and wherein said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) further includes a wavelength multiplexing portion (67,68) configured to produce multiplexed radiation by combining radiation from said radiation generator with radiation from said further generator before said radiation from said radiation generator passes through said non-reciprocal optical part, said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) being configured to route said multiplexed radiation through said non-reciprocal optical part and then through said single aperture; wherein the apparatus further includes an eyepiece portion (41, 42); and wherein said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) includes a thin-film structure which is disposed optically between said aperture and said non-reciprocal optical part, said thin-film structure being highly transmissive to radiation having said selected wavelength, and being partially transmissive and partially reflective to radiation having said further wavelength, said thin-film structure being configured to reflect along an optical path toward said eyepiece at least a portion of visible radiation received through said aperture, and a portion of radiation received at said further wavelength through said single aperture. a radiation generator configured to emit radiation having a selected wavelength; a radiation detector configured to detect radiation having said selected wavelength; an optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) which includes a non-reciprocal optical part, said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) being configured to route radiation emitted by said radiation generator at said selected wavelength through said non-reciprocal optical part and then through a single aperture toward a location remote from said apparatus, and to route radiation received through said single aperture at said selected wavelength through said non-reciprocal optical part and then to said radiation detector; and a further generator configured to emit radiation at a further wavelength different from said selected wavelength; and wherein said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) further includes a wavelength multiplexing portion (67,68) configured to produce multiplexed radiation by combining radiation from said radiation generator with radiation from said further generator before said radiation from said radiation generator passes through said non-reciprocal optical part, said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) being configured to route said multiplexed radiation through said non-reciprocal optical part and then through said single aperture; wherein the apparatus further includes an eyepiece portion (41, 42); and wherein said optical portion (16-18, 21-23, 67, 77, 52, 57, 67, 68) includes a thin-film structure which is disposed optically between said aperture and said non-reciprocal optical part, said thin-film structure being highly transmissive to radiation having said selected wavelength, and being partially transmissive and partially reflective to radiation having said further wavelength, said thin-film structure being configured to reflect along an optical path toward said eyepiece at least a portion of visible radiation received through said aperture, and a portion of radiation received at said further wavelength through said single aperture.