An optical device includes a transmitter, which emits a beam of optical radiation, and a receiver, which includes a detector configured to output a signal in response to the optical radiation. An active area of the detector has a first dimension along a first axis and a second dimension, which is less than the first dimension, along a second axis perpendicular to the first axis. An anamorphic lens, which collects and focuses the optical radiation onto the active area of the detector, has a first focal length in a first plane containing the first axis and a second focal length, greater than the first focal length, in a second plane containing the second axis. A scanner scans the beam across a target scene in a scan direction that is aligned with the first axis, and directs the optical radiation that is reflected from the target scene toward the receiver.