• 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 = $\frac{L}{f_o}$(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 = \frac{L}{f_o}$$\frac{D}{f_e}.

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