phase contrast microscope

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A microscope that uses the differences in the phase of light transmitted or reflected by a specimen to form distinct, contrasting images of different parts of the specimen.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a microscope that uses the change of phase when light is transmitted or reflected from a transparent or reflective specimen to form an image; used especially to study living cells