# Magnifying power v/s magnification

Why is it that we prefer to use magnifying power instead of magnification for optical instruments like microscopes and telescopes?

Related Classical Physics News on Phys.org
I believe "magnification" refers grammatically to the object being imaged. To say that a microscope has a magnification of 10 times would technically imply that we have a picture of the microscope zoomed up. To describe the tool doing the magnifying instead of the image, we then need a different term, such as magnifying power.

Drakkith
Staff Emeritus
From wikipedia on magnification:

Magnification is the process of enlarging something only in appearance, not in physical size. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one it refers to a reduction in size, sometimes called "minification" or "de-magnification".
and magnifying glass:

The magnification of a magnifying glass depends upon where it is placed between the user's eye and the object being viewed, and the total distance between them. The magnifying power is equivalent to angular magnification (this should not be confused with optical power, which is a different quantity) The magnifying power is the ratio of the sizes of the images formed on the user's retina with and without the lens
It looks like Magnification is the PROCESS of magnifying something, while magnifying power is a way to measure the magnification.

Because technically when your object is at the focus of a lens, the magnification is infinite, but the image is infinitely far away, so what's important is the angular magnification or what's in the parlance, magnifying power, which is the ratio of the angular size of the object with the lens divided by the angular size of the object placed 25 cm in front of the unaided eye (this is the largest you'll see the object in focus).

In equations, magnification is $m=\frac{y_i}{y_o}=\frac{x_i}{x_o}$, while magnifying power is $MP=\frac{\alpha_i}{\alpha_o}=-25(\frac{1}{x_i}-\frac{1}{f})$ where subscript i stands for image, subscript o stands for object, y is the height, x is the distance to the lens, f is the focal point, and alpha is the angle with respect to the axis of lens.

Last edited: