The following chart presents a comparison between the tested Tamron and Panasonic and Sony model we've mentioned in the introduction. The Tamron is physically a bit lighter than the Sony, with fewer optical elements, but it remains the longest in this group as well. The Panasonic sticks out with the most favourable minimum focusing distance and a compact barrel – a result of the slowest aperture.
In the photo below the Tamron 17–50 mm f/4 is positioned between the Voigtlander Apo-Lanthar 2/50 and the Sigma A 35 mm f/1.4 DG HSM.
The tested lens starts with a metal mount that includes contacts and a 33 x 24 mm frame. Inside that frame you get a rear element of the lens, 27 mm in diameter. The element moves; it is positioned several milimeters under the frame with the focal length set at 17 mm and, after passing to 50 mm, it hides as much as 4 cm deep inside, revealing a black, well-matted tube and some electronic parts. As you can see, the lens is neither fully sealed, nor perfectly blackened inside.
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The proper body of the lens is covered by black plastic; it starts with an immobile, smooth ring that doesn't move, with a silver band, a marking, making an alignment with a camera easier, the serial number of the lens, and informaton that it was made in Vietnam.
The ring increases its diameter very quickly and already on its enlargened part you find an USB port that allows you to connect the lens to a computer, allot different functions to its buttons, correct the autofocus, or just upgrade the newest version of software with the help of the Tamron Lens Utility program. On this part of the lens you can also find the producer's logo, the name of the lens, its parameters, A068 model number, along with information that it was designed in Japan.
A zoom ring is the next part of the lens, almost 34 mm wide, most of its surface covered by rubber ribs. On the ring you can also find focal length markings at 17, 20, 24, 28, 35, and 50 mm.
Movements of this ring change the position of the front element. For extreme focal lengths it is situated right below the filter thread mount, near 27 mm focal length it hides the deepest, being about 2 cm below the edges of the external barrel.
Further on you see an immobile part of the barrel, with a round, programmable button.
A manual focus ring, as wide as 16 mm, and completely covered by ribbing but without any distance or/and DOF scale is the next part of the lens. The ring, a focus-by-wire construction, moves smoothly and is properly damped. Its focus throw amounts to 80-90 deg and it depends weakly on the speed of your turning. It is a relatively low value but, fortunately, the lens offers you a significant depth of field, making manual setting easier.
The lens ends with a hood mount for a petal-type hood, inside which there is a filter thread for filters as big as 67 in diameter. The front element is slightly convex, 40 mm in diameter. As we've mentioned earlier, it moves inside the barrel, being at its shallowest with the lens set at the extreme focal lengths, and hiding inside the deepest near 27 mm. The side tube that is revealed in the process, is nicely blackened, matted and ribbed.
When it comes to the optical construction you deal here with 15 elements positioned in 13 groups. The producers weren't skimpy when it comes to special glass elements. Inside you can find three LD (low dispersion) elements, and three aspherical ones, manufactured with the help of different methods. Inside the construction there is also a round aperture with nine blades that can be closed down to the value of f/22 at the maximum. It's worth adding that the construction of the Tamron is moisture-resistant and the lens features a hydrophobic fluorine coating that is supposed to protect the outer part of its front element from oil residue of fingerprints.
Buyers get in the box with the lens: both caps, and a petal-type hood.
