An optical image is formed in a radiation-sensitive layer (5), by a number of sub-illuminations, in each of which an array of light valves (21 25) and a corresponding array of converging elements (91 95) are used to form a pattern of spots (111 115) in the resist layer in accordance with a sub-image pattern. Between the sub-illuminations, the resist layer is displaced relative to the arrays. Bright and well-defined spots are obtained by using effective lenses (43) as converging elements. The radiation-sensitive layer may be a resist layer on top of a substrate wherein a device is to be configured by means of lithography or an electrostatic charged layer used in a printer.