• Tags: compound-microscope, objective, eyepiece
• Difficulty: Moderate

A compound microscope uses two convex lenses: an objective (short focal length, small aperture) and an eyepiece (moderate focal length).

The objective forms a real, inverted, magnified image just inside the focal point of the eyepiece. The eyepiece then acts as a simple microscope.

Magnification (image at near point): M = (L/f_o)(1 + D/f_e), where L is the tube length (distance between the lenses minus f_o and f_e approximately).

Magnification (image at infinity): M = (L/f_o)(D/f_e).

For high magnification: f_o and f_e should both be small, and L should be large.