Coordinate Conventions

Coordinate convention:

1. Assume z axis is along central axis of the lens in this diagram, and the positive axis points to the right (away from the world).
2. The origin is at the z-intercept of the lens interface closest to the world (not shown on diagram).
3. All coordinates (D_X, D_F, etc) are given as the z-intercept.  Example: if the point on the target in focus is 10 mm to the left of the front of the lens and the film is 100 mm to the right of the front of the lens, then D_X = -10 mm and D_X' = 100 mm.
4. Please treat distance D is a signed value D_P' - D_P.  Hence if D_P' is to the left of D_P, D will be a negative number.