What is magnification?

Answer 1

Magnification is a mathematical ratio representing two physical relationships (or perceived physical relationships in the case of a virtual image):

1) the size of the image relative to the size of the object

2) the image distance relative to the object distance (from the mirror or lens).

The ratio calculated as given above in the first answer, M= -i/o is also equal to the absolute value of the ratios of the heights: M = -d_i/d_o = | H_i / H_o |

(where "d" denotes "distance", "i" denotes "image", "o" denotes "object", and "H" denotes "Height". Note that "p" and "q" are also used to represent "object" and "image", respectively, in some texts)

This equation implies that M is more than a mathematical relationship of the image to object distances, and that the value of the ratio has meaning about the actual image. There are four possible physical (or virtual) image characteristics that can be ascertained once the value M is obtained:

1) a negative value of M represents an inverted image.

2) an absolute value between zero and 1 indicates an image size that is smaller than the object size.

3) an absolute value of exactly 1 indicates an image size that is identical to the object size.

4) an absolute value greater than 1 indicates an image size that is greater than the object size.

Answer 2

Magnification is a dimensionless value given by the equation m = -i/o where i is the image distance and o is the object distance. The negative is of convention to denote an inverted image and a positive m denotes an upright image.