04-25-2017 08:43 PM - edited 04-25-2017 08:45 PM
BTW, I tested, and retested several times, my super telephoto lenses in a large, empty parking lot. I needed a mega-sized ruler, at 50x the focal length.
The stripes on the empty parking spaces worked out very well. If you're not getting consistent results, from one day to the next, then your testing methodology is too sloppy to draw any firm conclusions.