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Sigma 105 mm F2.8 DG DN Macro Art: very strange AF
Yesterday I had the pleasure to deal with a blossomed bush populated by dozens of butterflies too busy at feeding, so they didn't mind my presence - and everything at eye level, so I could test the Sigma 105 mm F2.8 DG DN Macro Art for several minutes without stressing my back.

And now I can confirm that the AF is strange. Focusing to subjects at about 40-50cm (even though EXIF data actually says the double...) was basically impossible - I'm not saying that the lens was hunting, even though it also did that: _it was never able to lock focus_. To be more specific: while it was driving the floating elements back and forth I never saw the focus plane passing through my subject, so the problem was that it wasn't trying short distances. It was fine if I tried to lock a subject at a longer distance. Of course this time I triple checked the focusing limiter, and it was set to full range.

The lens is not faulty: of course I did check it up to the 0.295m closer limit when I unpacked it, and again five minutes ago. It is absolutely fine with the flowers on my balcony. But there is some kind of subject that tricks it into error (I'm still investigating what could it be: perhaps being in bright light with bright background, or perhaps the shape of some plant...). Sony α6600 attached.

At a certain point I switched the AF from AF-S (single) mode to AF-C (continuous)... and this fixed everything. Not only it was able to quickly get a focus lock on the subject I was picking, but it also effectively tracked the butterflies slowly moving on the blossoms. Out of dozens of shots I only had sharp photos.

In a way it's fine for me, because it got the job accomplished.

But isn't this strange?


Sony a6300, Sony a6000, Sony NEX-6, Sony E 10-18mm F4 OSS, Sony Zeiss Vario-Tessar T* E 16-70mm F4 ZA OSS, Sony FE 70-200mm F4 G OSS, Sigma 150-600mm Æ’/5-6.3 DG OS HSM Contemporary, Samyang 12mm Æ’/2, Sigma 30mm F2.8 DN | A, Meyer Gorlitz Trioplan 100mm Æ’/2.8, Samyang 8mm Æ’/3.5 fish-eye II | Zenit Helios 44-2 58mm Æ’/2 
Plus some legacy Nikkor lenses.

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