Method of performing tomographic imaging of a sample in a charged-particle microscope

A charged-particle microscope comprising

• a charged-particle source, for producing a charged-particle beam that propagates along a particle-optical axis;
• a sample holder, for holding and positioning a sample;
• a charged-particle lens system, for directing said beam through the sample so as to form an image of the sample;
• an image detector, for capturing said image in an imaging step;
• an apparatus for adjusting a focus setting of the beam relative to the sample;
• a computer processor, for mathematically processing input images in a reconstruction step, so as to form an output reconstructed image;
• and
• a processing apparatus controller programmed to control the charged-particle microscope for:
• providing a beam of charged particles that propagate along a particle-optical axis;
• providing the sample on a sample holder that can be tilted relative to said beam;
• in an imaging step, directing the beam through the sample so as to form and capture an image of the sample at an image detector;
• repeating this procedure at each of a series of sample tilts so as to acquire a corresponding set of images;
• in a reconstruction step, mathematically processing images from said set so as to construct a composite image of the sample,
• wherein:
• in said imaging step, for a given sample tilt, a sequence of component images is captured at a corresponding sequence of focus settings;
• in said reconstruction step, for at least one member of said series of sample tilts, multiple members of said sequence of component images are used in said mathematical image processing.