A77 Micro-focus adjust, method and results…

Started Oct 23, 2011 | Discussions thread
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Yemble
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A77 Micro-focus adjust, method and results…
Oct 23, 2011

I had planned to calibrate my lens using a moiré focus chart on a tripod, but after some trial and error I concluded that real life photographs would provide a better measure. So I lined up a bag of compost in my garden and then took handheld shots from a distance, of the text on it, whilst braced firmly against the kitchen door frame. For each lens, I took a series of shots from -10 to +10 in steps of two and then methodically homed in on the sharpest setting. I did this at both ends of the zoom range using the widest aperture available, then took various other shots to confirm the final adjustment. Note that the weather was overcast giving a flat uniform light throughout.

Results were as follows:

+2 Tamron 28-75mm f2.8
+2 Tamron 70-200mm f2.8
+0 Tamron 17-50mm f2.8
+8 Tamron 90mm Macro f2.8
-3 Sigma 10-20mm f3.5-f4
+0 Sony 16-50mm f2.8
-2 Minolta 100-400mm APO f4.5-6.3
-4 Minolta 70-210mm f4
-1 Minolta 28-105mm f3.5-4.5
-2 Minolta 50mm f1.7
-2 Minolta 28mm f2.8

The first three Tamrons are all registered by the A77 as being the same lens, so it was lucky that the 28-75mm and 70-200mm both have the same adjustment of +2. The 17-50mm is effectively superseded by the Sony 16-50mm, so I probably will not use it. The big surprise was the +8 adjustment required by the Tamron 90mm at f2.8. Because I usually use this lens in manual mode, I had not noticed its relatively poor AF performance… now fixed My Beercan has been improved somewhat as well.

All in all, a worthwhile exercise and a big thumbs up for the A77.

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