This lens is very usable for nature shots, panoramas, sports like snow&skateboarding (you can "blow" the skater into the sky, because of the UWA perspective), architecture and funny portraits (I messes around quite a bit with my friends). I can only highly recommend this lens to anyone who needs an UWA lens. The price is very good too.
Below are the samples taken with Canon 400D. The field of view when mounted on 400D, is equivalent to 16-32mm on a full frame camera. From the crops you can judge image sharpness (center and border) for yourself. All the samples have slo-foto.net watermark, don't get alert - I made the test for that site and I'm the author of the photos.
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F6.3, 1/100, 10 mm, ISO 200
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On the sample above you can see some CA
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F6.3, 1/25, 20 mm, ISO 100
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F5.6, 1/50, 20mm, ISO 100
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F7.1, 1/30, 10 mm, ISO 100
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F4, 1/13, 10 mm, ISO 800
Below you can see two examples of how UWA perspective can be used. Train appears to be infinitely long and the sky is also "stretched":
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F6.3, 1/80, 10 mm, ISO 100
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F8, 1/320, 10 mm, ISO 100
If you're interested in studio part of the test (resolution chart) it's available here . All the shots were taken by Sandi Pelko. All the paramaters were set to 0 (sharpness, saturation etc), mine (taken outside) were set to the standard picture styles (sharpness 3 (on a scale 0-7, where 3 is really a normal setting). So the studio shots may seem a bit softer.
Pros:
-sharpness
-fast&silent AF
-price
-built quality
Cons:
-vignetting at 10-15 mm
-border sharpness at 20 mm
HIGHLY RECOMENDED.