A photo produced with a single thin lense is provided. Only based on the photo I should calculate the diameter of the lense.
The photo shows a ruler in the foreground and a point source of light in the background. The point source is blurred and has a size of 3.5 cm on the ruler.
My problem with the question is that the diameter of a lense is not used in any common formulas because it does not change how light rays traverse the lense.
I hope to find out how the diameter of a lense alters the projected image or preferred a formula containing the diameter of a lense.