Final answer:
In a bright field microscope, light from an illuminator passes through a condenser lens and focuses on a specimen, creating contrast. The objective lens magnifies the specimen, and the ocular lens further enlarges this image for the viewer to see.
Step-by-step explanation:
The optical path of a conventional light microscope, also known as a bright field microscope, starts with an illuminator, typically a high-intensity bulb that provides intense light necessary for viewing highly magnified specimens.
Light from the illuminator passes upward through the condenser lens, which is located below the stage and focuses all light rays on the specimen. The specimen, placed on a glass slide, absorbs some of this light and transmits others, creating contrast.
The objective lens, positioned just above the specimen, magnifies the object and creates a real image. This real image is then further magnified by the ocular lens, or eyepiece, usually by an additional factor of 10, resulting in a much larger virtual image perceived by the viewer.
Adjustments for focus and light intensity are made using various knobs, with the condenser focus knob optimizing the distance for maximal illumination, while a diaphragm and possibly a rheostat control the quantity of light that reaches the specimen.