Final answer:
A phase-contrast microscope uses an annular stop to create high-contrast images of transparent and unstained specimens by employing destructive interference, making structures appear dark against a light background.
Step-by-step explanation:
The type of microscope that uses an annular stop is the phase-contrast microscope. This type of microscope is designed to utilize the phenomenon of interference and refraction to enhance the contrast in transparent and unstained specimens. It operates with an annular stop, which is placed in the condenser. This stop creates a hollow cone of light, which only allows light that has been diffracted by the specimen to enter the objective lens. In the phase-contrast microscope, a phase plate in the objective causes some of the light to be approximately half a wavelength out of phase. This results in destructive interference when wave peaks and troughs cancel each other out, making structures in the specimen appear dark against a light background. This is particularly useful for detailed observations of living cells and organisms.