I am looking for a quick and easy DOF aid or calculator that will only take abou t 15 seconds to use (once I'm comfortable with it) and will give me a quick appr oximation of the best f-stop. I've seen the Rodenstock calculator/slide card an d found it too complicated to be of any practical use. I do a lot of near/far c ompositions, tilting to find the best compromise plane of focus. What tool do I use to help me decide the best f stop? Also, when there is more than one plane that I want to keep in focus, how do I decide which is the best plane to focus on or how to compromise between the various planes as well as using an appropria te f-stop? I don't want to carry around a polaroid back -- are any of these cal culators/cards really good, light and easy to use? Finally, if I want super sha rp prints, up to 20" x 30" and am shooting 6 x 9 format, what is the appropriate circle of confusion? Thanks for your help. Howard.