Magnification of optical microscope

Magnification in physical terms is defined as "a measure of the ability of a lens or other optical instruments to magnify, expressed as the ratio of the size of the image to that of the object". This means, that an object of any size is magnified to form an enlarged image.

The magnification required to produce the visible image can be calculated using the formula:


 * Magnification = Image ÷ Object

It is important that the all the units are in unison so that the final answer obtained is correct.

Optical microscope magnification
An optical microscope (or light microscope) uses visible light and lenses to magnify objects that are not visible to the naked eye. The magnification of a light microscope is formed using a mixture of the powers of the eyepiece and the objective lens. The eyepiece produces a power of 10x and the objective lens can produce various different powers, so if it were to produce a power of 100x, the final magnification would be 1000x (10 x 100). So this would mean that to the naked eye, the image would appear 1000 times larger than it actually is. Light microscopes generally have three different objective lenses to allow the slide to be viewed in three separate manners. Such microscopes are known as compound light microscopes. The objective lenses on a compound light microscope may have powers that start of as 4x on the smallest power, 10x on the middle power setting and 40x on the maximum power setting. This means that the object can be magnified either, 40x, 100x or 400x.

Empty magnification
Empty magnification is the phenomenon that shows us that increasing the magnification past a certain point results in no higher increase in resolution. So although the image will be more magnified, the resolution will remain low. This would therefore result in the image being very unclear. In fact, an increase in magnification past the optimum point could result in things such as visual artefacts appearing. These are substances which are not natural to the object and have arisen during the preparation of the slide being viewed.