Scientist using a scanning transmission electron microscope (STEM). A STEM combines the good image contrast characteristics and lack of lens aberrations of a scanning electron microscope (SEM) with the high resolution of a transmission electron microscope (TEM). An image is formed by a beam of electrons which is generated at the top of the instrument's column & then travels down through the specimen. The low-power binocular microsope is used to make fine-focus adjustments to the image. Here, the scientist is calibrating the STEM with a standard grid specimen in the Biology Department at Imperial College, London.