# lens equation

With
f = focal length,
g = distance to object (measured from object side principal plane H)
b = distance to image (measured from image side principal plane H’)

The so called “lens equation” reads ## Solving for focal length ## Solving for distance to object ## Solving for distance to Image ## Interpretation of the lens equation

What can be derived from this formula?

• The Image of infinite distant objects is in the focal plane.

When the object moves to infinity (= when g gets infinitely large), then Say, • An object that is at double focal length distance on object side is mapped to an image that is in double focal length distance on image side.
• In other words : If we want a 1:1 mapping in distance X from the sensor you have to choose (but subtract the distance of the principal points from X)

• If the object distance equals the focal length then the image is at infinity.
• The closer an object coming from infinity approaches the focal length, the closer get image distance and focal length. So holds.
• An object in focal length in front of the lens is mapped to infinity on image side.
• For an object closer to the lens than the focal length holds, say, the image is generated on the object side (!) of the lens.