Compound Microscope

A compound microscope uses a very short focal length objective lens to form a greatly enlarged image. This image is then viewed with a short focal length eyepiece used as a simple magnifier. The image should be formed at infinity to minimize eyestrain.

The general assumption is that the length of the tube L is large compared to either fo or fe so that the following relationships hold.

In a working microscope, the length L in the sketch above is much longer than either of the lens focal lengths fo and fe.

ExampleLinear and angular magnification
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Lens concepts

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Microscope Example

The general assumption is that the length of the tube L is large compared to either f(o) or f(e) so that the following relationships hold.

For tube length L = cm,

objective focal length fo = mm

and eyepiece focal length fe = mm

then the magnification can be approximated as follows:

Linear magnification of objective
= mo =

Angular magnification of eyepiece
= Me =

Total magnification = M =

The tube length and the objective and eyepiece focal lengths may be changed. This calculation is the standard form which is usually quoted for microscopes, but it is an approximation which may not be a good one under certain circumstances.

Examine approximations
 Index

Lens concepts

Optical instruments
 
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