1. A method of determining a fixed pattern noise of an image converter, the method which comprises: converting a first optical image comprised of a multiplicity of image elements into digital image data using the image converter; determining a light level for the first optical image from the digital image data; comparing the light level determined for the first optical image with a threshold value; if the light level equals or falls below the threshold value, changing the settings for the image converter to a dark image setting and thereby choosing the dark image setting such that the image data generated in the dark image setting in the case of a homogeneous distribution of a light level corresponding at most to the threshold value over a photosensitive imaging surface of the image converter does not include any component produced by the light level; recording a first dark image with the image converter in the dark image setting and using the first dark image in determining the fixed pattern noise of the image converter; and recording at least one further dark image analogous to the first dark image and replacing the digital image data for the image elements of the first dark image by the digital image data for the image elements of the further dark image, if the further dark image has a lower value, corresponding to the respective image elements of the first dark image.