A fluorescence laser scanning microscope, for scanning a laser over a specimen plane, comprising: a detector; a laser as a light source part; and an optical system arranged to guide light from the light source part to the specimen plane and to guide light from the specimen plane to the detector, wherein the optical system comprises: a light path switching unit (10, 13) arranged to switch a light path between the light source part and the specimen plane between two light paths with different routes along at least a portion of the light path between the light source part and the specimen plane; and two light deflecting units (11, 12), each arranged for changing the direction of the light to scan the light from the light source part two-dimensionally across at least part of the specimen plane and each being disposed in a respective one of the light paths, characterised by: a dichroic mirror as a light separation unit arranged on each of the light paths between the light source part and the specimen plane adapted to separate light from the light source part from light from the specimen plane to be guided to the detector; and a first light deflecting unit of the light deflecting units comprising a controllable galvanometer scanner and a second light deflecting unit of the light deflecting units comprising a resonant galvanometer scanner, wherein the light path switching unit is operable to switch the light path so that light from the specimen plane is guided to the detector via the controllable galvanometer scanner. a detector; a laser as a light source part; and an optical system arranged to guide light from the light source part to the specimen plane and to guide light from the specimen plane to the detector, wherein the optical system comprises: a light path switching unit (10, 13) arranged to switch a light path between the light source part and the specimen plane between two light paths with different routes along at least a portion of the light path between the light source part and the specimen plane; and two light deflecting units (11, 12), each arranged for changing the direction of the light to scan the light from the light source part two-dimensionally across at least part of the specimen plane and each being disposed in a respective one of the light paths, a light path switching unit (10, 13) arranged to switch a light path between the light source part and the specimen plane between two light paths with different routes along at least a portion of the light path between the light source part and the specimen plane; and two light deflecting units (11, 12), each arranged for changing the direction of the light to scan the light from the light source part two-dimensionally across at least part of the specimen plane and each being disposed in a respective one of the light paths, characterised by: a dichroic mirror as a light separation unit arranged on each of the light paths between the light source part and the specimen plane adapted to separate light from the light source part from light from the specimen plane to be guided to the detector; and a first light deflecting unit of the light deflecting units comprising a controllable galvanometer scanner and a second light deflecting unit of the light deflecting units comprising a resonant galvanometer scanner, wherein the light path switching unit is operable to switch the light path so that light from the specimen plane is guided to the detector via the controllable galvanometer scanner. a dichroic mirror as a light separation unit arranged on each of the light paths between the light source part and the specimen plane adapted to separate light from the light source part from light from the specimen plane to be guided to the detector; and a first light deflecting unit of the light deflecting units comprising a controllable galvanometer scanner and a second light deflecting unit of the light deflecting units comprising a resonant galvanometer scanner, wherein the light path switching unit is operable to switch the light path so that light from the specimen plane is guided to the detector via the controllable galvanometer scanner.