An Introduction to the Laboratory

Magnification

The term magnification may be used in two ways:
  1. Magnification of the Microscope
This refers to magnification of a microscope or a particular lens system within the microscope. Magnification used in this fashion tells you how much a certain optical system magnifies an object being viewed.
  1. Magnification of an Illustration
This is used when referring to an illustration (drawing or photograph) of an object. In this way, the term magnification tells you how the size of the illustration compares with the actual size of the object.

Magnification of the Microscope

The magnifying power of most objectives and oculars is engraved on them. On the ocular, the marking can be found on the top edge or on the smooth cylinder that fits inside the body tube; on the objectives, magnification is engraved on the side of the cylinder. The marking '10x ' means that the particular lens system generates an image ten times larger than the object being viewed.

The focal length, or working distance, is the distance from the object at which the objective lens is in focus. This distance varies for the different objectives (scanning objective, 25 - 50mm; 10x objective, 5 - 10 mm; 40x objective, 0.15 - 0.60mm). Note that for the 40x objective the lens is in focus less than 1mm from the object so this lens operates very close to the slide. In this way, you must take special care that this objective does not touch the slide or the lens may be scratched.

Magnification of an Illustration (Drawing or Photograph):

In using a microscope it is important to be able to determine the actual size of an object being viewed. This is normally done via calibrating the microscope by viewing an object of known size, such as a graduated scale on a slide.

Click here to review calculation of actual size

Once the actual size is determined the magnification of a drawing or illustration may be calculated using the following formula:

Magnification of the Illustration = Size of Illustration / Actual Size

For example, a magnification of 1x means the illustration is the same size as the object, 100x means the illustration is 100 times the size of the object, etc. It is important that you first calculate the actual size of an object, and from that calculate the magnification of illustration you have made of the object.

First published Sept 95: Modified June 2019
Copyright © Michael Shaw 2019 (Images and Text)

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