The invention relates to a computed tomography method for forming images of an object to be examined which is arranged in an examination zone. The examination zone is scanned by means of a conical X-ray beam. In order to enable images having a high image quality to be formed from a selected imaging zone while making an as small as possible computational effort, the invention proposes the following steps: a) selecting an imaging zone of the object to be examined, b) determining the sub-regions of the X-ray detector on which the imaging zone of the object to be examined is projected during the acquisition of the projection data, c) forming sub-projection data by selecting the projection data associated with the sub-regions from the acquired projection data, and d) reconstructing the desired image from the sub-projection data by backprojection.