First off I am not a math wizzard to figure Fstops, angles, filter adjustments that require math. I have seen a few or should say heard of a few programs that go on your Palm or Handspring that you imput the info and it does the work for you.
I have Bob Wheeler's Vade Mecum loaded on my clunky, old Palm V, and it's a great program. You'll need to read the docs, though, and perhaps carry a cheat-sheet for what the symbols mean.