Your best bet for quickies is to commit a few common conditions to memory. As in: "My 50mm at Xpaces at f/x.x provides Xfeet of in focus area, and Xfeet at x+2 paces", for each of your lenses. Once you know those you can wiggle around each memorized point with a few degrees of freedom.








Maybe one day each camera will have a little range-finder and an in-viewfinder display of present DOF size.