The Lens Equations

The Thin Lens Equation is the formula that demonstrates the relationship between the focal length, f, the object distance, d_o, and the image distance, d_i. See below for their definitions.

d_o: the distance from the object to the optical centre
d_i: the distance from the image to the optical centre
f: focal length of the lens: the distance from the optical centre to the principal focus.
h_o: height of the object
h_i: height of the image

The aforementioned relationship is expressed through this formula:
1  + 1  = 1
d_o    d_i     f

 This chart shows when the variables are positive and/or negative:

This is another explanation.

This page has the following sub pages.

• The Magnification Equation