SEL 55-210 Back-Focus on a6000

Started Oct 20, 2014 | Discussions thread
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Chrisd999
Chrisd999 Senior Member • Posts: 1,033
SEL 55-210 Back-Focus on a6000

Well, I thought the days of threads about back-focusing lenses were long behind me with the switch from DSLRs to mirrorless, but here I am starting such a thread, unfortunately.

Shooting with my a6000 and SEL 55-210 combo on the weekend I noticed a number of images, primarily at the long end, where the subjects consistently were just not "tack sharp". In one shot I took at 185mm, with the subject some 200 feet away, I noticed the image was much sharper (almost "tack sharp" about 30 to 40 feet behind the subject.

So I set up the crude battery test at home focusing using Single-shot autofocus (AF-S) with the focus area set to the moveable single point (Small) centered on the Duracell "D" of the middle battery. The front (right) and rear (left) batteries were spaced about 9" in front of and behind the middle battery. The camera was set up on a tripod about 15 feet away and was shot on 2 second timer, OSS off, 210mm, f6.3, Av mode.

The centre crops of results as you can see below were very repeatable. Although I was focusing on the middle battery the auto focus came out more accurately on the rear battery. The first 3 images below show the result using the AF, and the last image is manual focus. I did test at shorter lengths and at shorter subject distances and the focus accuracy improved significantly compared to 210mm and farther away.

To me the test result is consistent with what I was getting out in the field, and is not acceptable, and I am planning to exchange the lens. I hope the new lens I get does not have the same back-focus issue. I'm curious if any one else has come across back-focus issues on their NEX or aplha mirrorless cameras and lenses?

AF #1

AF #2

AF #3

Manual Focus

 Chrisd999's gear list:Chrisd999's gear list
Sigma DP1 Merrill Sigma DP2 Merrill Sigma DP3 Merrill Olympus E-M1 II Olympus M.Zuiko Digital 45mm F1.8 +10 more
Sony a6000
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