I checked the method again today with the 300 f/2.8 series II plus extenders using a high contrast black cross on white in good light. In all cases, the dot method was way out. Recalibration using the same target and sloping ruler was within 1 unit of previous.
Can you elaborate on the difference in target+methodology you're using between DotTune and whatever MFA method you're using for "recalibration"? For DotTune are you tuning to a flat DOF vs a 3-D DOF using the other MFA method? I'm asking because when DotTune is used against a flat target with no DOF reference (chart on wall), then you're tuning an unknown point within the DOF plane. It could be you're tuning at the very edge of the DOF range but you wouldn't be able to know this from a flat target. The alternative would be to DotTune against a target with a 3-D DOF reference, like a LensAlign target. I'd be appreciative if you could try this and report back the results. Thanks!
Please explain to me what a 3-D DOF ref is and how I obtain one. I would like to get your method to work. For the sloping ruler method, as well as using the + target and lampshade, I have printed the FoCal target. It's not that I do not know what 3D is, but I have never seen a LensAlign target, which I assume may be a low relief 3D, and I do not understand why a 3D target is necessary when a 2D target works for the do it yourself sloping ruler method etc.
« Last Edit: February 16, 2013, 03:08:23 AM by AlanF »
5D III, EOS-M, Powershot SX50, 300/2.8 II, 1.4xTC III, 2xTC III, 70-200/4 IS, 24-105, 15-85, 100-400 II, Sigma 10-20, EOS-M, 18-55, f/2 22.