Damn! beaten to the post by a millionth of a billionth of a degree!

That formula was on the tip of my tongue for ages .. but I added a +2 at the end, where he used +1.
Couldn't work out why my formula made the edges of the images less sharp than expected.

Doh!




Saying that 'it's all Greek to me' would be meaningless(as I have a Greek heritage anyhow, and the occassional Greek phrase does register ) .. so it's all astropneumatic rocket surgery to me.

As long as it makes cheaper lenses ...