Question

the circle of light that can be seen when you look through a microscope is known as
field of view
diaphragm
objective magnification
parfocal

Explanation:

The field of view is the circular area of light visible when looking through a microscope. The diaphragm controls light intensity, objective magnification is about how much the specimen is enlarged, and parfocal means objectives remain in focus when switching between them.

Answer:

field of view