After two years of owning the A850, I finally got around to Micro adjusting most of my full frame lenses.
Results seem to be very good and to have improved most of my lenses to the point that I doubt if I would purchase another camera that did not have this feature. I do expect that I may have to readjust some lenses slightly as time goes by. All reading were taken with the camera on a tripod and using 2 second delay with mirror lockup. Micro adjusting can be performed on the A850/A900 cameras and I believe the A77.Here are my results
Sony 28-75mm F/2.8 SAM = -5
Sony 70-300mm F/4.5-5.6 G SSM = -2
Minolta 28-135mm F/4-4.5 = -2
Minolta 70-210mm F/4 (Beercan) = -7
Minolta 28mm F/2.8 = -3
Minolta 50mm F/1.7 = -0
Minolta 100mm F/2.8 macro = -1
Minolta 300mm F/4 HS-APO G = -3
Minolta 500mm F/8 reflex = -16
Sigma 21-35mm F3.5-4.1 = -3
The first thing I noticed is that all adjustments were negative numbers. Could this indicate that most, if not all lenses, suffer from back focus problems (rather than front focus) to varying degrees. However it may just be a coincidence.
I also noticed that prime lenses were by far the easiest to adjust, having only one focal length. I checked them at maximum aperture and at around f8, also at close to the MFD and at a distance, depending on the focal length and type of lens (macro etc) and found little to no difference at these extremes.
Zoom lenses however varied a little bit at minimum, middle and maximum focal lengths, but mostly only by -1 to -2. I settled on the adjustment required for the sharpest result at max. aperture and at the focal length that I use most for the particular lens being tested.
I also found that all lens adjustments could vary by a very small amount if I focused the lens to infinity and/or to close focus prior to taking the reading. From that I realized that this is not an exact science but rather an exercise in compromise.
The Sony 28-75mm F/2.8 SAM required -5 which was a surprise, as it is my newest lens. The Minolta 70-210mm F/4 (Beercan) required -7, not a surprise for such an old lens. The oldest lens however, the Minolta 28-135mm F/4-4.5, only required -2.
By far the biggest surprise was the Minolta 500mm F/8 reflex at -16. Perhaps that is why I never used it much, hopefully it will earn it's keep from now on. When first tested, bearing in mind that at f8 it had a relatively large depth of field, all of the sharp area was in the positive or back focus range.
Sharp focus, although not the only requirement for a good lens, is possibly the most important, certainly the most discussed. So I think this test and adjustment was time well spent.