Most 16, 17 or 18mm-to-something-mm lenses show very noticeable barrel distortion at their widest focal length. This lens has barrel distortion at 18mm, but it performs better than many similar lenses by showing only a modest amount. As usual, the barrel distortion is corrected as the focal length increases until essentially being gone at around 22mm. Pincushion distortion then creeps into the picture and becomes mild from 28 through 35mm.

Overall, I am very pleased with the image quality from this first-ever lens design. It has a green light for my own needs.

Featuring Sigma's HSM (Hypersonic Motor) driven AF, the Sigma 18-35mm f/1.8 DC HSM A Lens focuses with very good speed.

At short distances, this lens is practically parfocal (focus distance settings remains the same throughout the zoom range). Longer distance focusing likes more focus adjustment through the available focal length range.

The Sigma 18-35mm f/1.8 DC HSM A Lens has very smooth, perfectly-damped and ideally-sized zoom and focus rings that have no play in them

http://www.the-digital-picture.com/Reviews/Sigma-18-35mm-f-1.8-DC-HSM-Lens.aspx

Comparison with Rokinon 35/1.4 and Canon 24-70 f2.8L

Interview with one of lens constructor

Q: Does an access to low dispersion glass of different kind (SLD, FLD) or high refraction index glass make the work of an optics specialist noticeably easier?

A: Although low dispersion glasses are essential optics for the development for high performance lenses, using them does not explain the whole story of the success. Adequate experiences and flexible ideas are essential for lens design as it enables us to grasp the features of each optic and optimize them in the product.

Q: Why the Sigma 18-35 mm filter is 72 mm in diameter while its moderately convex front element is only 49 mm in diameter? Was it impossible to use a smaller filter?

A: Although it may not be possible to attach the 49 mm filter, attaching a frame close to that size is possible. However, the frame of the filter will cause vignetting in the edges thus it's not realistic.

Q: How the optical stabilization influences the resolution of an image? After all in such a construction there are movable elements. Is designing stabilized lenses more difficult than designing ordinary lenses?

A: We think that the optical stabilization system reduces camera shake which affects resolution. Because the optical stabilization system needs to move some of the lens groups, the lens design with OS function will be more difficult from both optical and mechanical points of view.

Q: More and more cameras, launched on the market, are mirrorless constructions, characterized by short flange focal distances. Of course such a situation demands a quite different approach to the lens construction, especially when it comes to telephoto lenses. Do you still look for new technical solutions in an active way when it comes to the optics or are the coatings the only innovation here? Or maybe the construction process is just like playing with Lego blocks, modifying slightly the same proven constructions over and over again?

A: Concerning telephoto lenses for mirrorless cameras, it's important to take the design of AF system into consideration. Rather than flange focal distance, to function the lens groups and the optimized mechanical design is more substantial element for a lens development. There are many ways to improve lens performance apart from optical technology. Thus, we are always working on any type of development for our technical innovation. Conventional designing methods have also some room for improvement, so our engineers are refining their skills by studying it thoroughly.

http://www.lenstip.com/136.1-article-Interview_with_constructor_of_Sigma_lenses_Interview_with_constructor_of_Sigma_1.4_35_and_18-35_mm_f_1.8_lenses.html

Amazon just sent me a note saying they still don't have stock, so it looks like this lens is delayed. Maybe some heavy demand?

Yeah, I have the same lens, good old Vivitar Series 1 (with macro setting), OM mount of course.

That is a big lens, love to see it mounted on a GH2. Might need a lens support, particularly with u43 adapter.

Sigma 18-35mm f1.8 is worth every penny bringing top of the line build quality, amazingly wide apertures, zoom abilities, and fast autofocus for only $799.

http://learningcameras.com/reviews/4-dslrs/166-sigma-18-35mm-f18-hsm-lens-review

Yep, also this data is added to dpreview lens review at

http://www.dpreview.com/previews/sigma-18-35-1-8/3

and here on a T4i:

The Sigma 18-35mm F1.8 DC HSM is a fast and tack-sharp lens from F2.8 onwards, and one that exhibits low chromatic aberrations. Vignetting at wide-open apertures and barrel distortion at 28mm are the only real optical issues of note, something that other fast wide lenses also suffer from, and stopping down to F4 solves the light fall-off problem altogether.

Build quality is also excellent, with the brass lens mount and sober all-black design adding to the high-quality feel, and Sigma have even generously included a very good lens hood and padded case. The internal HSM focusing was very quick on the Canon EOS 700D that we tested the lens with, and manual focus over-ride at any time is a great feature.

http://www.photographyblog.com/reviews/sigma_18_35mm_f1_8_dc_hsm_review/

All the photos I have seen show the lens with electrical contacts (probably photos of EF mount). I emailed them about the Nikon version having the physical iris lever and got this confirmation:

Hello, The lens has a mechanically controlled lever actuated diaphragm and we are just starting to ship it in the Nikon mount this week. Yours Truly, Paul Pizzano Sigma Corporation of America

In German, and unfortunately no video samples. Just stills.

Performance starting from wide end

http://www.ephotozine.com/article/sigma-18-35mm-f-1-8-dc-hsm-a-lens-review-22257