Infra-red focussing control for SLR camera - has optic correction for infra-red w.r.t. visible light and objective setting

摘要

The object is illuminated by an infra-red source on the camera while the infra-red spot is focussed inside the camera and viewed in the viewfinder. In order to compensate for the focussing difference between infra-red and visible light special monitors monitor the objective setting and operae a compensating linkage to bodily move the infra-red source ro to move a compensating filter in front of the source. The differences of focussing which have to be compensate 1 for depend upon the focus distancing even with the same object. The differences are, however, so small that by the use of an intermediate, constant corrector the variations can be kept well within the depth of field.