1. Method of determining distortions in a particle-optical apparatus, said apparatus equipped with: a particle source for producing a beam of particles along a particle-optical axis; an object holder for holding an object, said object holder capable of translating an object placed in said object holder; a projection system for forming an image of said object, and a detector for acquiring and storing the image of the object, the method comprising: providing an object; acquiring a first image; determining the distortions, such that in the first image a sub-image is defined, the first sub-image showing a portion of the object; a series of images is acquired, the object being translated between each of the acquisitions; the realized translation between the images is determined; in each of the images a sub-image showing the portion of the object is identified; the sub-image distortions of the portion of the object shown in each of the sub-images with respect to each other is determined, and the sub-image distortions of the portion of the object shown in each of the sub-images is used to determine the distortion of the image.