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Full Version: The Sigma 14mm f/1.8 ART ...
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.. has arrived in da lab ... the review should be up by late next week.

FWIW ... after having used the lens out there over the weekend - the experience tells me - once again - that DSLRs and EOS cameras in particular just can't focus accurately with ultra-wides. The margin of error is HUGE and, of course, it was especially bad with this large aperture Sigma lens.

Things are fine with close-ups but for middle-ground scenes (2-3m) things are going down the hill rapidly. The camera is just focusing too far to the rear.

Hmm, I don't remember such issues with the Canon EF 11-24mm f4, yet I do remember some having issues with for instance the Sigma 35mm f1.4 Art, and others having issues with some Art lenses on Nikon. 

Yeah, I'd put the blame on that EOS camera too.

Switch to manual focus and observe how "long" the camera thinks that something is in focus at such wide angles ...

 

To be fair - the 14mm f/1.8 is an extreme lens.

Quote:FWIW ... after having used the lens out there over the weekend - the experience tells me - once again - that DSLRs and EOS cameras in particular just can't focus accurately with ultra-wides. The margin of error is HUGE and, of course, it was especially bad with this large aperture Sigma lens.

Things are fine with close-up but for middle-ground scenes (2-3m) things are going down the hill rapidly. The camera is just focusing too far to the rear.
 

 Wide angle lenses seem to cause the most focus problems and Sigma have forged themselves a reputation for AF inconsistencies with repeatability issues with some of their recent lenses, large apertures should have helped to some extent. When calibrating AF on a zoom I start at the wide end where the adjustment make the greatest difference. 

  But even my Sigma 150mm tele-macro suffers, it does very well until you get to less than 3 mts......then it front focuses agogo, at 2.5 mts you need like -17 then it quickly goes to the max setting with still not enough compensation.........it's just enough to spoil it as a portrait lens (at least one you can rely on)

  At macro distances it's fine again!

  

 

 

   But I don't want to unearth a can of worms here......please? :mellow: .....let's use another thread for that!

I'm surprised how much keepers I get with that lens on the D850 contrary to what I got out of the combination D810 and 20/1.4.

Since I use AF-C most of the time, I can hear when the camera's AF gets clueless about my target. Fabric surfaces, rounded edges, shiny reflections... Otherwise only difficult targets can become impossible ones.


If it seems to be impossible, because AF keeps hunting, I switch to LV and 100% view to focus manually. Seeing how much I shake around, I get an idea what the camera's/lens' combinations problems look like. I can't blame the lens or AF alone, part of that system is me. And the amount of shaking of my hands plays a big role in the so calles focus inconsistencies. Now dave, you don't have as much Art lenses as I do, but I'm aware that if I say I can't confirm what you claim as forged reputation for AF problems, that doesn't say much. Statistically I'm irrelevant. Statistically the ones with AF problems could become relevant, if we knew, how high the percentage actually is, what these owners do with their lenses and how much up to the task their cameras are. Usually I'm only complaining about problems, not telling or counting these lenses which just work.


For me, I'd sum up this way: AF basically is not to be trusted in critical situations, but in general still more helpful and also more reliable than manual focused. On a DSLR, that is. On the Fuji, when I could narrow down and adjust the location the focus field, am comstantly in LV and could switch to manual focus, things would be much different. So, yeah, don't expect too much AF reliability on wide open ultra wide angles on a DSLR.
Quote:Switch to manual focus and observe how "long" the camera thinks that something is in focus at such wide angles ...

 

To be fair - the 14mm f/1.8 is an extreme lens.
OK, that is a good thing to look at. Indeed, the camera, with this lens, then also is "at fault". Does this lens, by chance, with its f1.8-ness, show a lot of aberrations wide open?
     That's what I termed the AF-C "dead band" the distance you can move the camera before the camera refocuses, when I got the DA*16-50mm back from repair for a new SDM motor, I thought it still had a problem, such was the DOF fooling the system.

 

  Pentax's  dead band is huge compared to Nikon!

I did lots of in-room shots yesterday (Sydney Open event). Thx to the bad weather many rooms were rather dark (but still way within AF specs). That in combination with the DoF fooling was a bit beyond of what the camera was capable of. Things were fine in decent light.

 

It's all a far lesser issue with something like the 11-24mm f/4, of course, but at f/1.8 and relatively short focus distances even a 14mm has a fairly shallow DoF.

Yeah, for this kind of shooting I bought that lens. This weekend I also did lots of in-room shots with incandescent, LED and other artificial (also pretty poor) lightings. On one side the keeper rate of all lenses went lower, to my surprise the 135/1.8 struggled a bit more than I hoped on the D850. But then I also have to say, I got sharp shots where I would have failed to focus manually. I wished it would be perfect and I also wished I'd knew more about how to help the AF doing a better job. Like, which colors to aim at, if I have a choice. When it's better to move the camera a bit and when I should aim for steadiness.
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