A permanently sealed vacuum tube is used to provide the electrons for an electron microscope. This advantageously allows use of low vacuum at the sample, which greatly simplifies the overall design of the system. There are two main variations. In the first variation, imaging is provided by mechanically scanning the sample. In the second variation, imaging is provided by point projection. In both cases, the electron beam is fixed and does not need to be scanned during operation of the microscope. This also greatly simplifies the overall system.