Chapter 11 - Optical Systems - Section 8: Microscopes

11.8.1 Simple Microscope (Magnifying Glass)

A simple microscope is a single positive component used to magnify an object, when the object is located at or within the focal point of the component. The magnification of microscopes, both simple and compound, is somewhat arbitrarily defined as the ratio of the apparent angular size of the image to the angular size that the object would subtend if viewed from a distance of 10 in, which is assumed to be the distance of most distinct vision (on the average).

Assuming that the eye is located close to the lens, the simple microscope of Fig. 11.35 has a magnification of

When the object is placed at the focal point, s' is infinite, and M = (10 in)/f. If the object is within the focus by a distance such that s' = -10 in, then M = 1 + (10 in)/f. These relationships are conventionally used to define the power of magnifiers and eyepieces for telescopes and compound microscopes.

11.8.2 Compound Microscopes

A compound microscope consists of an objective forming an intermediate, usually magnified, image and an eyepiece to view, and further magnify, the image. From the definition of magnification above, and with reference to Fig. 11.36, the magnification of a compound microscope is

or

Note that there are instances where the magnification may not be clearly defined by either the telescope or microscope conventions. If the object is neither at infinity (or at a great distance) nor close enough that it could be viewed at the distance of most distinct vision (10 in), quite different results will be obtained if the conventional magnification formulas are applied. The proper magnification under such circumstances is still the ratio of angular size of the image to the angular size of the object at a distance determined by the application.

11.8.1 Simple Microscope (Magnifying Glass)

A simple microscope is a single positive component used to magnify an object, when the object is located at or within the focal point of the component. The magnification of microscopes, both simple and compound, is somewhat arbitrarily defined as the ratio of the apparent angular size of the image to the angular size that the object would subtend if viewed from a distance of 10 in, which is assumed to be the distance of most distinct vision (on the average).

Assuming that the eye is located close to the lens, the simple microscope of Fig. 11.35 has a magnification of

When the object is placed at the focal point, s' is infinite, and M = (10 in)/f. If the object is within the focus by a distance such that s' = -10 in, then M = 1 + (10 in)/f. These relationships are conventionally used to define the power of magnifiers and eyepieces for telescopes and compound microscopes.

11.8.2 Compound Microscopes

A compound microscope consists of...