Quote Originally Posted by Ian C View Post
For a 6-element symmetric lens at enlarger distances this is usually about 2.6% greater than the actual focal length. So if you substitute the approximate equivalent thin lens focal length of 107.7mm you’ll get a more accurate estimate.
Hi Ian, how do you arrive at 2.6% greater? That seems to be a proper lens "rack out" at about 38X magnification. I don't see how the lens design (symmetric) would affect this?