Equipment, processing, feel and function = 4 stars
The 10 - 20 EX DC HSM 3.5 f of SIGMA is a great visual tool specifically calculated for the APS-C format.
First impressions: First-class feel, with extra carrying case and lens hood, fine. The optical component along with a full 520 grams on the scale, the surface is very noble, the label has been applied clean, everything looks extremely dibasic.
The front lens does not rotate during focusing, fortunately with so that the filter cartridge is no impediment. Unfortunately, the filter size is 82 mm in diameter unusually large, which increases the cost of appropriate visual aids. In addition, the 82mm filter size is not a common size. In principle, a wide-angle capture has a large front lens to the mighty Wide area usually. Typically, this is also convex. In that regard, I strongly recommend to use at least a UV filter as a sort of protective lens to secure the sensitive front lens.
An image stabilizer is not installed. But at least a Silent Wave drive for fast and silent autofocus was donated. The autofocus works properly, readjustment is not necessary.
The zoom range of 10 to 20 mm does not seem great, but in the world of wide-angle makes this quite a bit of viewing angle. The service works perfectly well, the build quality is outstanding. Mechanically really a dream. With the correct torque without air between the moving elements. 5 stars for this performance.
Imaging performance - Picture Quality = 4 stars
For me personally, the question arose, how it behaves with the distortion, so I first would like to dedicate this topic.
Compared with the fainter SiGMA 10-20 mm, 4 - 5,6f, DC EX HSM the 3,5er in 10 mm focal length range listed but violent. The "initial ton" then falls over in a slight cushion in the central region. But some like this barrel-shaped arches as a design element to give more width, is thus a matter of taste. Since I am reluctant to elaborate rumkorrigiere PC, it was important to me to find a lens, which lies in the discipline from distortion front. And I do not like extra sheets in the picture. But I have to admit that the "Distortion-cushion" when 3,5er in 20mm focal length range wiedrum smaller fails. Therefore, in the discipline distortion I give in the sum like 4 stars.
The sharpness convinces everybody. The lens scores with above-average sharp imaging performance. I have concocted me a corresponding test structure and Scan with tripod, simply in order to achieve reasonably comparable results. Depending on the aperture used can be a very good depth of field and resolution are generated. Even some bokeh can be represented. In principle, exactly the same sharpness as the 4-5,6er of SIGMA. But there are differences, because, amazingly, the sharpness in the center over the entire focal length range even with maximum aperture is above average. For the sharpness an extra plus, thus yields the in this discipline a 5 star + rating!
Chromatic aberrations can only be shown. Especially at medium focal lengths, even in low-beam mode. These are recognizable and traceable on PC at magnifications. Since the fainter counterpart has already compared advantages. For 3 stars.
Another aspect in the field of image quality are vignetting, thus shadowing the edges. With super wide angles sometimes a problematic discipline. I suppose as a "DUT" a large white wall from neighbors. As with the 4-5,6er sister vignetting can be seen in the 3,5er optics in 10 mm range and maximum aperture (3,5). Fade help but clear. 3 stars
Tip: Use filters in slim design, ie particularly flat representative, otherwise you have to expect a strengthening of vignetting. I use filters from Hoya, these are type technically kept very flat and provoke no additional vignetting.
The brightness offered but again brings significant advantages mitsich, especially when using a polarizing filter. An ISO value increase is rarely necessary. Here that has 3.5 against the 4-5,6er clear advantages. 5 Stars.
Thus resulting in the discipline Bildquälität very good 4 stars and an extra plus for the razor-sharp images.
The excellent sharpness, in strong light are an important argument. Unfortunately, recorded in super wide angle at 10mm focal length significantly, whereas in the upper half in 20mm with a relatively low distortion can be seen. Ca`s are not entirely prevent vignetting and fall only 10mm in`s weight.
Value = 3 stars
Items in the network move below the RRP but it is significantly more expensive than the 4-5,6er SIGMA, in an almost identical image quality! The filter thread size of 82mm provokes high costs for such tools. With the equipment and the image performance but 3 stars in price money are good to represent!
Conclusion: Rating = 4 stars (3.6 and an extra +)
Those looking for an extreme wide-angle lens with class profile for the APS-C format, will find it here. It is significantly brighter than the in-house lens sister, scores with a great focus, but you have to be able to live with distortion in the 10mm range. Who edited on computers a lot, but so have little problems, as I said, some use the arcs also a design element to make rooms appear even bigger. Images appear visually brilliant and sharp crack. It is in spite of the 10mm Fisheye no, that makes sure once more the fascination of these Sigma lenses from. Wide spaces can be delightfully captured in pictures.
The zoom range is perfect for everyday use. I have not bought it because I have personally given to the minimal distortion of the fainter objective more value and 3,5er is significantly more expensive. All interested parties but I can recommend buying a good conscience.