# Magnifying power v/s magnification

1. Jul 29, 2011

### thebiggerbang

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

2. Jul 29, 2011

### chrisbaird

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.

3. Jul 29, 2011

### Drakkith

Staff Emeritus
From wikipedia on magnification:

and magnifying glass:

It looks like Magnification is the PROCESS of magnifying something, while magnifying power is a way to measure the magnification.

4. Jul 30, 2011

### RedX

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: Jul 30, 2011