Sony 10-18mm f/4 and 16-50mm Samples from NEX 7

Started Nov 15, 2012 | Discussions thread
jpr2 Forum Pro • Posts: 15,514
re: critically accurate focusing & the myth of UWA "enormous" DOF

technic wrote:

jpr2 wrote:

Many UWAs and WAs behave similarly, and my strong suspicion is that the SEL 10-18 is no exception

yes, more or less what I have seen too with many different SWA lenses. However, it depends on the lens design. My Canon 15-85 (24-135 effective) is sharp in the corners even wide open for shorter focus distance like 5 meters, but pretty soft in the corners for infinity subjects. I tried adjusting the focus with Liveview for best corner sharpness at infinity, but this doesn't give any improvement. The rendering in the corners does change a bit when adjusting focus, while in the image center I see no change at all; probably the design is optimised for closer distances than infinity ...

  • our whole (and sometimes substantial, going back many decades) photog. experience tells us to expect a "huge" DOF from UWA lenses - and... it was correct during film era;
  • however, with the EF-S 10-22 I was already getting quite bizarre effects pretty often on a lowly 400d with its 10 Mpx sensor - simply put what was captured and what DOF calculus predicted were two different things;
  • same story with 40d; which was slightly improved on 7d thanks to MFA and its better focusing screen;
  • but only on N7 + manual assist magnification enabled me to document its very complex behavior = very much depending on WHERE in the frame an actual critical focusing was done;
  • focus in the center, and infinity will be sharp, but closer objects will not fall into sharpness ranges of what DOF calculus predicted;
  • focus at the far corners and we will get the results I've demonstrated earlier in this thread [sic !!];
  • in both cases, however, the actual images and the DOF ranges will not tally with each other, sometimes quite substantially;

in the neighboring discussions abt. 10-18 and 16-50 there are plenty of posts proclaiming quite categorically that accurately critical AF in the UWA/WA region of such lenses is not important because... of their huge DOF - however, the actual evidence pretty often denies such utterances

And yet it will take still some time, perhaps in conjunction with much more widespread experiences of using UWAs on sensors in the range of 24-36 Mpx and up, before the legend of a very forgiving "huge" DOF of UWAs will finally wear thin Obviously, though, prevalence of mustachioed profiles will​per force ​accelerate the spread of a better understanding of factors involved.


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