[quote name='BG_Home' timestamp='1290341651' post='4302']
I'd agree with you if that stayed the same even after the lens is shifted. But given that using the lens unshifted is like using an FF lens on a crop sensor (because it's designed with a larger image circle), you'd expect the corners to be of decent quality when the lens is not shifted... no?
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No, not necessarily. By definition MF lenses have lower resolution than FF or APS-C lenses, and in a rectilinear lens the large AoV makes for losing definition and therefore sharpness towards the corners at an alarming rate, and that is pure optics laws at work.
I reckon this is a lens which is diffraction limited at all apertures, i.e., it is sharper than is physically possible to show in an image. When used as a pure 17 mm, non-shifted IOW, it just doesn't seem to lose definition at all towards the corners.
Regarding the corners: I found that shifted it is equally sharp to the Nikkor 14-24 in the corners (read: it starts smearing details a little, just like the Nikkor, although that's nothing compared to the Sigma 12-24 EX), just that it has probably a little more lateral CA in very high contrast transitions in those corners. Do note that with maximal horizontal shift it essentially becomes a 10.2 mm lens, which is quite a bit wider than the Nikkor at 14 mm, or even the Sigma at 12 mm. So, comparable sharpness to th eNikkor at full shift is quite a feat, if you ask me.
Here is a sample, handheld, shifted about 7-8 mm up to correct the worst of the converging lines (but keeping a little for a natural view), making this a 12 mm lens for AoV at the top here.
![[Image: castle09bw.jpg]](http://www.lumifer.com/fs/castle09bw.jpg)
BTW, my feet were only just outside the image.
In the full size image all details in the stone and grass in left and right top is preserved. It's really amazing how good this lens is, especially considering it is an extreme UWA....
Obviously, this image was processed. What I did here was a B&W conversion, contrast and brightness adjustments, some dodging for the underside of the supporting stone on top of the doorway (the weathering looked exactly like the cloud structure, so that was kinda neat - here the DR of the 5D II shows what it is capable of in combination with this lens), and some dodging for the tower and the path leading up to it. Oh, and some partial sharpening of the tower itself, 50%. Upon downsizing I had to use bicubic smoother rather than the normal bicubic sharper, because using bicubic sharper caused sharpening artefacts <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />. I couldn't believe it when I saw this, it really is stunning... Furthermore, this lens actually renders contrast excellently despite its large number of elements (18!), and has excellent microcontrast too, which makes it also stand out from the Nikkor. Despite being an UWA, this lens is capable of 3D-like images.
Hmm, we really hijacked this thread now for real. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />
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 ....
