The invention relates to a method of determining an aberration of a charged particle microscope. The method comprises a step of providing a charged particle microscope that is at least partly operable by a user. Then, a set of image data is obtained with said charged particle microscope. The image data is processed to determine an aberration of said charged particle microscope. According to the invention, said set of image data is actively obtained by a user. In particular, the image data may be obtained during normal operation of the microscope by a user, which may include navigating and/or focusing of the microscope. Thus, the set of image data is acquired by said user, and not by the controller thereof. This allows background processing of an aberration, and aberration correction during use of the charged particle microscope. The invention further relates to a charged particle microscope incorporating the method.