Quote Originally Posted by Jon Wilson View Post
If the FL is measured from the Waterhouse slot to the image on the wall it would be 28 inches and 23 inches from rear of lens.
If you're shooting wide open (with spherical aberration), measure from the lens. If measuring from a stop (blocking the spherical aberration), measure from the stop. That's how focus shift works, changing the focal length as you stop down. That's also how soft focus works, soft being one focal length, sharp being another focal length. And that's also how males and females work. Males and pixies, I'm not so sure...