Can someone layout, in the simplest terms possible, what distance away from the batteries I should be for each focal length? e.g. 24mm=15". I want the tests to be as accurate as possible. I tested from 11' away @ 70mm and I couldn't make out much.
If you would test this tamron at 1m (3,28 feet) at 24mm F2.8 you would already get 0.3m DOF (almost 1 feet).
It would be quit bad if it exhibited bad focus after correcting it at lets say 50mm!
If I were you I would do a test at 50mm , about 30 inches away from your subject (batteries) . Place the batteries not straight behind each other (as to exclude focus error due to camera picking wrong subject) but leaf a slight gap in between.
Also place the batteries exactly one inch behind each other. measured from the edge of the table.
Then take a picture from the edge of the table with adjustments +6 +8 +10 +12.
It will become quiet clear where the focus is moving itself when you leaf a little gap in between.
This gap (1inch) is slightly smaller than the dof=> but ofcourse when the focus is dead on the middle battery it will only span the depth between the front and back battery!!