Image position
This equation predicts the formation and position of both real and virtual images in thin lenses. It is valid only for paraxial rays, rays close to the optic axis, and does not apply to thick lenses.
1/(object distance) + 1/(image distance) = 1/(focal length)
The equation is:
1/o + 1/I = 1/f
Where:
o: Object distance
I: Formed image distance
f: focal length