Get the images into DPP, make the AF Points visible (Command + J on a Mac), and see where you are. I'm at -3 right now.ДЄlso, don't go off of the 5D3's LCD to see where your focus is hitting. In the end, I had a range of potential 'good' MFA values (-10 to 0), shot at each value in the range, and eventually landed on the best one.

Trees are my favorite tuning subject, since the bark is really contrasty, and the grass behind/in front can help you determine where the sharpest plain of focus is. To get my 50L dialed in I just did a LOT of shooting wide open, at objects with good texture and contrast, and eventually had an idea of where the AF was hitting the most (in front or behind target), and adjusted accordingly. Basically, FoCal can't get a consistent reading and therefore can't make an exact adjustment. It's recommended to MFA a lens at it's widest aperture, and I think that 50L gives the AF system issues due to the DOF of f/1.2 being smaller than the tolerance of the AF system. I plan to redo the 135L testing, this time from a correct, large distance.Д¦D, Tamron 24-70 f2.8 VC, 135L, 70-200 f4L, 50mm f1.8 STM, Samyang 8mm fisheye, home studio My other fast lens, 135L, looked fine at -1 MA, but I noticed recently that for my main usage of the lens (full height portraits, meaning you have to be really far, with my crop camera), f/2.0 shots are always very slightly off. My newest zoom, Sigma 17-50 OS, was tested to work fine at -2 MA, in real life environment. with a few shots at each zoom and each distance you can get a pretty good feel on what MA is needed. I didn't even need to use a tripod, remote shutter release, mirror lockup etc. Then I discovered that I get better results by hanging a large printed target on a wall in my backyard, and shooting it from realistic distances on a sunny day. ) of my lenses, and was never happy with the real life results. I spent a lot of time doing indoor testing (printed targets, computer monitor with moire patterns. From my experience, for best results in focus MA, one really needs to have the environment as close to real life shooting as possible - meaning both correct light (use daylight, not fluorescent / LED / tungsten), and distances (if the typical use of the lens is full-height portraits, the size and the distance to the printed target should be chosen accordingly).

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