Although this particular lens was first introduced in 2008 in the rest of the world, the Tokina lenses have not been very freely available in South Africa until recently.  There are currently six models to choose from, all available in both Canon and Nikon mounts.

The 11-16 f/2.8 in a Canon EF-mount is the first Tokina that I am field testing.  This particular lens is a wide-angle zoom built for Canon APS-C crop and Nikon DX sensor camera bodies (Tokina use the letters DX to indicate crop-sensor).
It a Canon EF-mount, it is ideal for the EOS 300/350/400/450/500/550/600D series, as well as the 10/20/30/40/50/60D series.  It also works perfectly on the 7D dslr body.
For Nikon users, it works very well on the Nikos D3000/3100/5000/5100/7000 series, and the D200/300/300s dslr bodies.  

The Tokina 11-16 f/2.8, as seen from the business end of the lens.  It is mounted here on a Canon 40D.


How Is It Built
My first impression of this lens is one of its superior build quality.
The Tokina 11-16 is heavier than one might expect, although the weight comes about as a result of the robust construction and the amount of glass needed to make a constant f/2.8 aperture lens.
From left to right, the Tokina 11-16 f/2.8 DX, the Canon EFS-10-22 f/3.5 and the Canon EF 16-35 f/2.8L II wide-angle zoom lenses.
At 560g it is substantially heavier than the Canon EF-10-22mm, which weighs 385g.  In fact, it is closer in weight to the Canon EF 16-35 f/2.8L II at 640g.
The weight balances perfectly on a medium-sized dslr body like the Canon 60D.
The zoom mechanism that the rest of the lens is built around, is made of metal, and covered in tough polycarbonate, with a smooth-textured finish to it.  The zoom and focus rings are wide, have deep ridges and are easy to locate or operate.  Both zoom and focus rings operate smoothly, with no sticking or play at all.  There is also no play in any other part of the lens.
The build and exterior finish of this lens is perhaps closer to a Canon L series lens than it is to Canon EF-S lens like the EF10-22.
There are no switches on the exterior of the lens barrel, and switching from AF to MF is accomplished by sliding the focus ring backwards or forwards.
There is a focus distance scale in the lens barrel.
The 11-16 comes with the BH-77 lens hood as standard.  The lens hood is made of hard black plastic and has a stepped finish on its interior surface, to reduce glare.  The exterior of the lens hood does pick up scratches quite easily, as do most black plastic lens hoods.  On the other hand, it mounts very firmly, and there is no play or rattling in the mount.

The front lens cap is spring-loaded, and is easy to attach or detach even with the supplied lens hood in place.

A frontal view of the lens, with the front lens cap in place, and the hood mounted.
The front of the lens accepts a 77mm filter, and mounting one provides protection for the front lens element, as well as reducing the chances of moisture or dust getting inside the lens.  The front element does not rotate during zooming, which means that filters like polarizers are easy to use on the Tokina.  There is also no change in the size of the lens during zooming.  The Tokina is not weather-sealed.
The front element has a special coating on it to disperse moisture from the glass itself, and this also means it stays clean for longer, and cleans up easier.
The rear lens mount is made of chromium-coated brass.
The lens mount on the Tokina AT-X 11-16 f/2.8 DX-Pro
How Does It Work?
This ultra-wide focal range actually compliments most kit lenses that come with many dslr bodies as the majority of them start at 17 or 18mm and go upwards from there.
On an APS-C camera like the Canon 60D or similar, the 11-16 represents an equivalent focal length of 18-26mm.

This lens has a very short zoom range, going from just 11-16mm.  In this respect it trades extra range for a consistency of image quality, and in fact the image quality is good across the entire focal length range.  For my purposes, I found the results to be similarly good at either 11mm or 16mm and anywhere in-between.

I have included two images shot one after another, at the two extremes of the lens focal range, to give an idea of the zoom range and field of view.

Tokina 11-16 f/2.8, Focal length 11mm, at f/7.1.
Tokina 11-16 f/2.8, Focal length 16mm, at f/7.1.
Although this particular Tokina does not operate with a focus motor of the same silent specification as the USM focus setups in many Canon lenses, it still worked well.  With such a short range and short focal length, the AF does not get challenged too much, and it was plenty good enough.  You can hear the AF motor work on the Tokina, but it is hardly noisy and AF was good enough that I could just get on with taking pictures with the lens.
Many Canon dslry bodies have central autofocus points that will operate at a higher level of precision when matched with a lens with an aperture of f/2.8 or larger.  The Tokina is just such a lens, and this is a big benefit, particularly when working in very low-light situations.  
In use the focus ring and zoom ring turn smoothly and feel well-damped.  The One-Touch clutch for switching from AF to MF is easy enough to use.  One merely slides the focus ring back toward the lens mount to disengage AF.  If the gears do not align properly, it may be necessary to turn the ring slightly until it slides back easily.  This system is easy to use, even with cold hands or with gloves on.
The focus ring movement is firm enough that it shouldn’t get shifted inadvertently whilst being stored or handled.
If you are shooting from a tripod, and like to first use AF to focus your shot, before switching AF off to take the pic, as some of us do when shooting long exposures, or images for panos etc, then be aware that when sliding the focus collar back to disengage AF, it is possible to cause the focus point to shift.  I normally make use of live view to check my focus in such situations anyhow.

Image Quality

Tokina 11-16 f/2.8, AT-X Pro, Canon EOS 550D, 1/800sec at f/5.6.
I used the Tokina 11-16 on a Canon 60D, 40D and a 550D during testing, and the lens worked very well with all three of those cameras.
The AF response was fast enough, on a 550D, to enable me to capture common dolphins racing alongside a boat.
Sharpness
The lens is acceptably sharp for my purposes and the equal of the Canon EFS 10-22mm lens that I have used extensively.  Landscape images taken with this lens responded well to my usual sharpening processing steps in Adobe Camera Raw and Photoshop.
Contrast
Despite the bright, overhead light, and strong, white reflections from the water splashes in the dolphin image, the resulting picture was of good quality.
Colour
Colours were rendered well, and contrast as good as other lenses in this class that I have used.
Distortions
Distortion was not very pronounced at all with this lens, even though some distortion is characteristic of all wide-angle lenses in this focal length range.  The distortion typically becomes most apparent when one is extremely close to a subject, and can be used for effect.  It also means that lenses in this focal range, the Tokina included, may not necessarily be ideal for photographing people up close.
Chromatic aberration
Tokina 11-16 f/2.8, 16mm focal length, 1/50sec at f/5.0, iso 640.
Heavy crop, top right corner of previous image.  Tokina 11-16,f/2.8, 1/50s at f/5.0, iso 640.
Chromatic aberration, or CAs usually show up in a picture along edges where very high contrast tones meet.  Most lenses are susceptible to showing CA’s given certain shooting conditions, but some more so than others.
As a nature and wildlife photographer, I know that when I photograph a tree canopy from below that has patches of bright sky showing through from above CA’s may show up as thin, coloured lines along the edges of the dark leaves and the very bright sky.
The Tokina 11-16 f2.8 shows some CA, noticeable around the edges of the frame, in such circumstances.
It is relatively simple to get rid of the effects of CAs, in post-processing, as Adobe Lightroom, Adobe Camera Raw and Photoshop all have a set of tools and sliders that help to minimize their effect.
The amount of CA that did show up whilst using the Tokina 11-16 was not enough in any way to hinder my ability to use the lens for taking high-quality pictures and during my review period, I never took or kept any images that were affected by CA in real-world use.
Flare
Tokina 11-16 f/2.8, 1/250s at f/11.
Canon EF 16-35 f2.8L II,  1/250s at f/11.

 

When photographing a very bright light source, or shooting towards it, it is possible that stray rays of light may be reflected inside the lens barrel.  The result of this is called flare.
Flare can cause a lack of contrast in an image, and it can show up as circular patches of very bright light, sometimes coloured.
Wide-angle lenses are a bit more susceptible to flare, especially due to their wide field of view, and the fact that it can be harder to avoid including a bright light source like the sun in an image.
In such circumstances, all the wide-angle  lenses I have used will show some effects of flare.  Unless I am looking to include the flare for effect, I typically do not choose to compose such images in the first place or I look to partially obscure the bright light source.
For the purpose of this field review, I took an image with a very bright sun in the frame, with both the Tokina 11-16 f/2.8 and the Canon EF 16-35 f/2.8L II lens.  Both lenses show the effects of flare, but the Canon, which costs about twice as much as the Tokina, is less affected.
Overall Image Quality

Whilst I have given over much attention whilst writing and illustrating this field review with images and explanations of chromatic aberrations and flare, for my own purposes both of these characteristics are of much less importance than one might believe, given how much space they occupy in the field review.
I don’t typically seek out compositions with areas of very high-contrast whatever gear I am using, and I spend even less time trying to photograph the sun directly.
So for my real world usage, I am more interested in whether the lens is sharp, captures images with good colour and contrast, and is easy to use.  The Tokina meets all of my image quality requirements easily.
The image below of the Jonkershoek mountains in the western Cape serves to illustrate this.

Tokina 11-16 f/2.8, AT-X Pro at 11mm focal length.  Canon EOS 60D.  1/320s at f/8, +1 exp comp, iso 200.

Overall image quality of the lens is very good and I had no hesitation in using it.

Conclusion
The Tokina 11-16 f/2.8 AT-X Pro provides Canon APS-C (and Nikon DX) shooters with something that no other ultra wide-angle zoom does, and that is the benefit of a constant f/2.8 aperture zoom throughout the focal range.  This can be extremely useful for those who need to shoot in very low light, or who need the extra shutter speed needed to stop action.
It delivers very good images, in a package that features build quality bested only by Canon’s L-series lenses, at a price that many may find attractive.

The 11-16 f/2.8 is also a fun lens to use, and I did not want to take it off my camera body at all.
I have no hesitation recommending it as a very good lens for shooting landscapes, wildlife (though you do need to be close to your subject) and for general wide-angle applications.