Planar focus correction

A desktop imaging device, comprising an electronic camera and a mount by which the camera may be mounted above an edge of a desk and directed down onto the desk in order to image a document on the desk, in which the camera has the following features:

• a detector array;
• an objective lens arranged to direct optical radiation from an object plane onto the detector, the lens defining an optical axis of the camera and the object plane being at an oblique angle to the optical axis;
• movement apparatus to change the relative orientation of the detector with respect to the lens so that the detector and lens may be moved relatively toward or away from each other along the optical axis and also tilted with respect to each other with at least one degree of freedom;
• a focus detection apparatus connected to the detector to detect when a portion of an image falling on the detector is in focus;
• and a processor to control the movement apparatus according to the detected focus, the processor bringing the image into focus on the detector by first changing the relative orientation of the lens and detector until a first portion of the image is in focus, and then holding said first portion in focus whilst continuing to change the relative orientation of the lens and detector until a second portion of the image is also in focus.