In the era of reflex cameras Tamron used to offer a lens with parameters identical to the tested Sigma. First, in 1997, it was released in adaptal version and three years later we saw a launch of its autofocus version, available with Canon EF, Minolta A, and Nikon F mounts. Sigma tried to compete in this segment with a slightly slower but also much lighter and smaller 28-105 mm f/2.8-4 DG model.
In the following chart the tested Sigma is compared to the Canon, mentioned in our introduction, two reflex camera models, described by us a moment ago, and the Sony FE 24-105 mm f/4 G OSS.
The Sigma sticks out in this group with as many as twelve aperture blades, and its minimum focusing distance, amounting to just 0.40 of a meter and remaining on the same level across the whole focal range. It allows you to get 1:3: mapping scale.
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In the photo below the Sigma A 28-105 mm f/2.8 DG DN is positioned next to a lens with equally interesting parameters, the Tamron 35-105 mm f/2-2.8 Di III VXD, and the reflex camera Sigma A 35 mm f/1.4 DG HSM.
The tested lens starts with a metal mount that surrounds the contacts and a rear element, 29 mm in diameter that doesn't move. The element is situated about 1.5 cm deep inside the barrel. Around it you see an inner tube which is properly blackened, ribbed, and matted so from this side everything looks very well.
The first part of the proper body of the lens consists of a smooth, black, ring, covered by matt plastics, that increases its diameter smoothly and quickly. It is a change when compared to the latest Sigma products – in other models this ring usually is smooth, shiny, and made of metal. Current solution seems to be more esthetic because it's more difficult to notice fingerprints, dirt, or scratches on such ring. The ring features a white dot, making an alignment with a camera easier, '024' number stating the model year of the instrument, and an inscription 'MADE IN JAPAN' along with the focusing mechanism working range „0.4M/1.31FEET–∞”.
An aperture ring, as wide as 18 mm, is the next part. The majority of its surface is occupied by ribbing but you can also find there aperture markings ranging from f/22 to f/2.8 and an 'A' value (meaning auto). The ring moves every 1/3 EV but you can make it clickless, undoubtedly an option intended to make filmmakers very happy. Overall the ring is a joy to use – no reservations here.
Further on you find an immobile part covered by plastics with the logo of the company, the name and parameters of the lens, its serial number, the A letter, meaning that the lens is classified and an Art line device, fine ribbing, and two switches. The first of them – CLICK- control the aperture ring mode. The second one is used to lock the aperture ring either at A position or in any other position in a range from f/2.8 to f/22.
The next part is a zoom ring, as wide as 28 mm, most of its surface covered by rubber ribbing. Under that you find focal length markings at 28, 35, 50, 70, and 105 mm. The ring works properly well, is smooth and damped across all its range.
Then you find an immobile part of the casing covered partially with fine ribbing. There are also two FOCUS LOCK buttons in that area, which are, additionally, programmable, a FOCUS AF/MF switch, and a LOCK switch, used for blocking the zoom ring.
A manual focus ring, almost completely covered by rubber ribbing and as wide as 33 mm, is the next part of the proper barrel. This ring is a focus-by-wire mechanism and its focus throw weekly depends from the speed of your turning, amounting to an angle of about 100-120 deg.
The Sigma A 28-105 mm f/2.8 ends with a hood flange inside which you find a non-rotating filter thread, 82 mm in diameter. The front element is immobile, relatively flat, with a diameter of 65 mm. With the increase the focal length the whole front optical system is pulled out on a homogeneous plastic tube. As a result the length of the lens increases by 41 mm.
The Sigma is weather-sealed, splash- and dust-proof. The front element is covered by hydrophobic coatings that prevent an easy adhesion of dirt, droplets of water, and grease.
When it comes to optical construction of the lens there are overall 18 elements positioned in 13 optical groups. Among them you can find two FLD elements with properties similar to fluorite, one element made of low dispersion SLD glass and as many as five aspherical elements. Inside there is also a round aperture with as many as 12 blades that can be closed down to a value of f/22 at the maximum.
Buyers get in the set: both caps, a petal-type hood, and a solid, hard case.
