Apertures (108) having references edges are situated to define a sample irradiation zone (131) and a shielded zone. The sample irradiation zone (131) includes a portion proximate the shielded zone that is conjugate to a detector (116). A sample (112) is scanned into the sample irradiation zone (131) from the shielded zone so that the sample (112) can remain unexposed until situated properly with respect to the detector (116) for imaging. Irradiation exposure of the sample (112) is reduced, permitting superior imaging and less damage to the sample (112). The sample can be translated longitudinally and rotated and an electron beam (104) can be used in order to form images by electron beam tomography.