1. A system comprising: a plurality of optical emitters disposed at approximately constant radius from a location to be imaged; an annular lens receiving the optical output from each optical emitter of the plurality of optical emitters and coupling these optical outputs to the location to be imaged; an adjustable shield disposed on the inner edge of the annular lens, the adjustable shield varying an angular range of optical signals from the plurality of optical emitters coupled to the location to be imaged.