Abstract: A laser transmitter unit is described, the unit including a laser diode 2 emitting laser radiation into a lens system. The lens system includes collimating lenses L1, L3 and focussing lenses L2, L4. Additionally, compensating or steering lens S1, S2 are positioned between the collimating lenses L1, L3 and the focussing lenses L2, L4. The steering lenses S1, S2 act to reduce the sensitivity of the focussing lenses L2, L4 to position within the lens system. The position of the focussing lenses can be difficult to control, particularly when the lenses are welded into position in the laser transmitter unit 1.