Abstract: An additional optical element with a positive optical power is used to influence an optical image produced by the camera lens on the image sensor by inserting the additional optical element between a camera lens and an image sensor of a camera, wherein the center thickness of the additional optical element and the optical power of the additional optical element are matched to one another in such a way that, for a predetermined diaphragm setting of the camera lens, a flange focal distance defined by the camera lens remains substantially unchanged by the insertion of the additional optical element.

Abstract: In a method for detecting smoke or fire in rooms, at least one image of the room is recorded and digitalized to a digitalized image. The digitalized image is compared to a reference image in digitalized form, wherein the reference image is generated based on an image of the room previously recorded and digitalized. The sum of image elements of the digitalized image deviating by at least one first threshold value from the reference image is determined. An alarm signal is generated when the sum reaches or surpasses a second threshold value. The device for performing the method has a video camera and a matching light source arranged in a dark field arrangement.