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The Sigma 14mm f/1.8 ART ...
#11
My EF-S 10-18mm f4.5-5.6 IS STM appears to focus correctly close by (~1.5-2meters) and pretty correctly further away (not sure, I remember it to be 6-7 meters away) on my 6D. Of course, only can try it at f5 max. Have to put them on the computer still, though, to check better.

#12
The f/1.8 makes a huge difference. Even at 3...5 metres away the DoF is not deep. And the higher the resolution the more a100% view shows missed focus although it doesn't look too bad at first look.


I was thinking about the focus abilities in artificial light. All of them do have kind of a frequency, be it 50 or 60 Hz or higher for fluorescent lamps (up to 200 Hz, I think). If the cameras refresh rate for the AF-module comes close to such a frequency or even synchronizes with, the worst what could happen is the camera only switches AF when the light also goes dark. The flicker reduction setting made me think about this frequency thing, but I don't know if the impact is big.
#13
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.
This is reassuring... For me. Smile Ever since I've got the Sigma 14/2.8 I've been struggling with its sometimes odd focus behavior on medium and longer distances. I used to think that it was either a flawed sample, a flawed design per we, or a flawed (aka dumb) operator behind the camera - but if it's none of the above (just the nature of the game), I can stop chiding myself and/or trying to get rid of the lens. Which, I might add, despite being from a very old generation of Sigmas, worked well otherwise on a range of bodies, from 40D up to 1D X.
#14
I reckon it is caused by the camera not being able to determine exactly what to use for AF exactly, as the AF points cover quite a bit more territory than they do with e.g. tele-lenses. Having a slower aperture helps a lot in those cases, I would think.

 

What may help is focusing on large contrast transitions, if any items can be found at the same distance as the subject one wants to focus on. This is something that not only works fairly well with extreme UWAs, but also when experiences very low light levels, IME anyway.

 

Kind regards, Wim

Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#15
That was about what I was thinking once I got the hang of it a little, Wim. When there's a large central subject, everything (mostly) works fine. Of course, one may argue that this is how you should be shooting an ultrawide anyway...

#16
Quote:...Of course, one may argue that this is how you should be shooting an ultrawide anyway...
 

Says who exactly?  :blink: In Klaus' gallery a lot of shots are not following that idea. And I'm also quite happy that the lens is so good and very usable at the borders.
#17
Quote:I reckon it is caused by the camera not being able to determine exactly what to use for AF exactly, as the AF points cover quite a bit more territory than they do with e.g. tele-lenses. Having a slower aperture helps a lot in those cases, I would think.

 

 
Almost never, there is something a lot in front of what you want to focus on with UWA lenses. It can be that you focus on a small target where behind it the background can become a target of the AF point. However, AF points are small enough to rule that out in tests. 

 

Spherical aberrations in a lens can throw off the PD AF system, depending on which colours the AF sensor is sensitive to. And the steps a lens makes can also be an issue.

In this case, from what Klaus describes, I suspect aberrations to be the/a culprit. Testing my 10-18mm on 14mm yesterday in MF, the focus confirmation range was very, very small.
#18
Quote:Says who exactly?  :blink: In Klaus' gallery a lot of shots are not following that idea. And I'm also quite happy that the lens is so good and very usable at the borders.
Ken Rockwell of course.  Tongue But most of the time, I tend to agree because it seems to me that ultrawide shots can look "empty" without a well defined (central) subject.
#19
Yes, but that emptiness might be part of what I want to say with the picture?

 

Like "ooh I'm missing a Rock Kenwell somewhere here"  :lol:

  


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