Originally posted by chromo What I mean is, for example :
The distance from the sensor to the mount is 45.46mm, If I made an extension tube 45.46mm long, would the image then be upside-down but still in focus and the same size on the sensor?
That can get a bit more tricky. You'd have to actually USE the program to experiment with various things like this. I can place the image plane at one particular value, and the program will focus for me (the way I'm describing it, it will determine the object distance). But to change values, you will need to use the program, I cannot really do all the permutations. And anything I do with a standard 50 mm design will not apply directly to another lens.
OSLO also has an education version, which is free (and yeah, it's Lambda Research's lens design program...) The manual also is, in itself, a lens design course. If you haven't done any college physics, though, it might be a little steep.
Maybe someone near you could meet you and assist?