= Solution
For <bright-field transmission electron microscopy>, place the objective aperture in the <back focal plane> around the transmitted beam, excluding most diffracted beams. Adjust the intermediate lens to image the objective's real-space image plane; projector lenses enlarge that image onto the screen or camera. Regions removing <electrons> from the admitted beam tend to be darker, although phase contrast can also contribute.
For <selected-area electron diffraction>, put the selected-area aperture in the objective image plane to choose a specimen region. Remove or open the objective aperture and change the intermediate-lens excitation to image the objective's <back focal plane> onto the camera. The projector then magnifies the diffraction pattern, rather than the specimen image. Thus the two apertures act in different conjugate planes.
\Image[/past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2020/paper-1-tem-modes.png]
{title=The plane selected by the intermediate lens determines TEM imaging or diffraction mode}
{source=paper-1-tem-modes.py}
<Selected-area diffraction by JEOL>[Area-selection aperture in the objective image plane and conjugate diffraction-plane imaging]{ref}
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