Let's eliminate the most probable variable - vibration. Tripods are useful tools but they certainly leave pleanty of possibility for unexplained issues.
Build yourself a couple of "sandbags". Ziplock plastic bags filled, literally, with dry sand work well. I've one 1/2 gallon sized heavy canvase sack filled with lead shot that provides a VERY steady platform. Put the plastic bags in cutoff pants legs or large socks if you chose to use smaller plastic bags.
Use a solid table, window sill, etc., for the base. Put one or two "sandbags" under the camera to isolate it from outside vibrations. Get a gnat's a$$ fine focus on whatever and set up for the 2-second delay shutter mode. Now carefully lay a second, lighter "sandbag" on top of the camera and have at it.
If you're still having questions about camera motion vs. lens performance with that setup, you either have vibration sources in the building or mechanical issues with the camera itself. You'd be surprised how much vibration a highway, a motor or an A/C compressor can cause. "Sandbags" can effectively dampen that, or at least change the harmonics to a harmless frequency. In any case, you've eliminated a major variable.
Another good vibration isolation trick is to use gel-type mouse pads - these are very useful in the field too.
When picking a test target, if you can lay a piece of window screening material beside the target and almost parallel to the sight axis you have a pretty good indication of practical DOF if the target's within the useful resolution of the image. I often used a 12-inch, fine thread brass rod from a broken lamp laid on a piece of screening as a quick 'n dirty, but consistent, DOF gage for bench-top close-up/macro work.
H2
That plastic water jug hung under the cheap tripod is a great "force-multiplier" too.
Last edited by pacerr; 05-29-2009 at 12:11 PM.