Which of the following parts of the microscope concentrates the light onto the microscopic slide?

A) Iris diaphragm lever
B) Substage illuminator
C) Fine adjustment knob
D) Condenser
E) Objective lens

Substage Illuminator

A light source located beneath the stage of a microscope, used to illuminate the specimen from below.

Iris Diaphragm

An adjustable aperture used in optical instruments, like microscopes and cameras, to control the amount of light passing through the lens.

Condenser

A device used to condense vapor into liquid, widely used in laboratory equipment, air conditioning, and power plants.