Hi, does this eqn holds? http://www.kowa-usa.com/digiscope/gr...alculation.htm
For example, I have a focal length of 1050mm and the diameter of lens is 70mm. So the f-stop will be approximately f15?
Canon EF 400mm diameter is 90mm. 400/90=4.44. Why is it f5.6? Does it only hold for digiscoping set-up and not DSLR lens?