Why is zoom provided in Tokina 11-16mm?
Tokina has specialized in zooms. The reputation of their AT-X lenses is basically built upon their acquisition of highly-regarded zoom technology from Angénieux. Their current lens lineup includes:
- Six primes: 20mm x2, 50mm, 100mm x2, 300mm.
- Fifteen zooms.
Like their primes, many of their zooms duplicate the same ranges. For instance, they have 10-17mm x3, 11-16mm x2, 11-20mm, 12-28mm x2. They have full-frame duplicates of crop-sensor lenses. One line (AT-X V) consists are near-exact duplicates with minor body modifications.
What's the point of all that? Consumers want and buy zooms. Lenses have different mounts and formats to match different cameras. The same lens can be sold at different prices. If someone is willing to pay more for a lens, why not sell it for more? But if the choice is between selling a lens for a bit less, but still substantial amount, vs not selling the lens at all, why not sell it for a bit less? By selling the same and similar lenses at different prices, they can do both.
Why not make it an 11mm prime lens instead? It would contain less elements, so will produce sharper images... its probably more complex to implement the zoom capability.
"Prime" does not necessarily mean fewer elements. Extra elements are required to correct distortions and aberration. Since the flange focal distance of most cameras is greater than 11mm, a reverse telephoto design is required, which also needs more elements. You may be interested in reading – Lens Rentals: Lens Geneology (part 1, part 2).
Lenses need to be only as sharp as the sensor is able to resolve. Modern zooms are much better than many primes from the era when zooms "earned" their poor reputation. By limiting the zoom range, the trade-offs to create the zoom are also limited.
Since Tokina has essentially specialized in zooms, they've already done most of the design work, especially when considering the duplicate models. Manufacturing is already complex. Increasing complexity a bit doesn't matter because people get good at tasks repeated often enough and much of it is done by machine.
Also at such wide angle, what difference this 5mm would provide anyway.
The difference is about that of full-frame and APS-C (16/11 = 1.45). In terms of pixels, it's about double – (16/11)2 = 2.12. Also, many Tokina zooms, including this one, are constant aperture, so there's no light-loss penalty for zooming.
If someone wants this little zoom...
They can buy the lens in question. There is generally high demand for zooms. They are versatile, and people can avoid post processing by "cropping" in camera. See ethics.
Is it some technical feasibility issue or I've got all these concepts wrong?
I am able to find one 11mm prime lens for sale, so it's technically possible to produce, but it's manual focus, has an F4 aperture, and listed for more than the Tokina 11-16/2.8 variants. There's probably not much demand for such a lens.
