The following chart presents basic properties of the tested lens and other full frame f/2.8 instruments which focal length starts from 28 mm and ends at 70-75 mm. In the majority of cases you deal with quite old devices; nowadays manufacturers tend to focus more on 24-70 mm plus f/2.8 parameters. When it comes to optical design, it might be surprising that the new Tamron is hardly more complex than older constructions but it definitely prevails when it comes to the number of special elements. It is also relatively lightweight and quite long but its width doesn't differ much from the widths of its rivals.
In the photo below the Tamron 28–75 mm f/2.8 Di III RXD is positioned between the Nikkor AF-S 24–70 mm f/2.8G ED and the Sigma A 35 mm f/1.4 DG HSM.
The tested lens starts with a metal mount with embedded contacts and a frame as big as 32.5x23 mm. Inside that frame you see a movable rear element of the lens, 31 mm in diameter. It is situated on the same level as the mount at 28 mm focal length; when you pass to 75 mm it hides about 2 cm deep inside the barrel, revealing a black, well-matted inner tube. Of course the lens cannot be called perfectly sealed from that side; on the other hand we haven't noticed any shiny electronic or casing parts either.
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The proper body of the lens is covered by black plastics and starts with an immoblie, smooth ring on which you can find a silver strip and a mark, making an alignment with a camera easier. The ring becomes wider very quickly and on its enlarged part you see an inscription with the name and parameters of the lens and information that the lens was designed in Japan but produced in China.
A manual focus ring is the next part of the lens; it is 15 mm wide and completely covered by rubberized ribbing. There is no depth of field or distance scale on it but the ring moves smoothly and is well damped. It is a focus-by-wire construction and even if you turn it very fast the whole working range covers an angle of about 180 degrees.
Further on you find a smooth, immobile part of the casing, 9 mm wide, and behind it a zoom ring, as wide as 37 mm and mostly covered by rubber ribbing. On that ring there are focal length markings at 28, 35, 50, and 75 mm.
If you turn that ring from 28 to 70 mm the size of the lens increases by 27 mm as the front element system, ending the construction, is extended on a uniform, plastic tube.
The front element is 57 mm in diameter, surrounded by a non-rotating filter thread, 67 mm in diameter, and a hood mount.
When it comes to optical construction you deal here with 15 elements positioned in 12 groups. The producers weren't skimpy with special elements – inside you can find one LD (low dispersion), one XLD, and three aspherical elements, including one hybrid and one molded glass element. Apart from that the lens features a round aperture with nine diaphragm blades which can be closed down to a value of f/22. It is worth adding that the Tamron's construction is described as moisture-resistant and it also features a hydrophobic fulorine coating which is supposed to make the outer element less vulnerable to damaging effects of dust, dirt, and fingerprints.
Buyers get just two caps with the lens in the box. It's a pity at this price you don't get also a hood or/and a case.
