The following chart shows a comparison between basic parameters of the new Sigma lens and other full frame macro instruments with similar focal lengths. The complexity of optics of the Sigma sticks out immediately. Despite the lack of stabilization it features more elements than its stabilized rivals and yet it is hardly the heaviest device in this group because the Nikkor and the reflex camera Sigma version are heavier. For a change, the Sigma A 105 mm f/2.8 DG DN Macro is the longest lens of all.
In the photo below the Sigma A 2.8/105 Macro is positioned between the reflex camera Sigma A 35 mm f/1.4 DG HSM and the Sony FE version of the Voigtlander Apo-Lanthar 2/65 Macro
The lens starts with a metal mount surrounding a contact plate and an inner tube inside which you see a rear element. That element doesn't move and positioned almost 3 cm deep. The inner tube around it is very nicely blackened and matted, with a lot of ribs. The rear element itself is set behind a black 28x22 mm frame. From this side everything looks great, the lens is fully sealed and very nicely blackened.
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The first part of the proper barrel consists of a sleek, black, metal ring which quickly and smoothly increases its diameter. On that ring you can find a white dot, making an alignment with a camera easier, '020' number meaning the model year, and an inscription 'MADE IN JAPAN' along with the minimum focusing distance 'MIN 0.295M/0.968FEET–∞'.
The next part is an aperture ring, 19 mm wide, most of its surface covered by ribbing. It features markings for all available aperture values (with smaller markings every 1/3 EV step) and an A point for the automatic mode. The ring can be declicked or it can turn every 1/3 EV step and you can control the mode of working with a special switch. Another switch locks the ring in place.
Further on you see an immobile part covered by plastics with the company's logo, the name and parameters of the lens, its serial number, fine ribbing, a letter 'A' meaning the device was classified as an Art line instrument, and a series of switches. The first of them – AF/MF FOCUS- allows you to control the focusing mechanism working mode and the second one – AFL- allows you to lock and recall a specific autofocus position. Other functions can be attributed to it as well. Further on you see an autofocus range limiter switch and here you have three ranges at your disposal, FULL, 0.5 of a meter – ∞, and 0.295-0.5. The next switch controls working modes of the aperture ring. On the side opposite to that array of switches you can also find a toggle that blocks the aperture ring.
A manual focus ring is the next and also the biggest part of the casing – it is as wide as 62 mm and mostly covered by ribbing that makes your grip firmer. You won't find any distance or depth of field scale on it. The ring is a focus-by-wire construction and it turns very smoothly but with proper resistance. Its focus throw amounts to at least 270 degrees, allowing you a good precision of settings.
When you work in the 1:1 projection scale the photographed object is situated in a distance of a bit above 14 cm from the front element. The front element itself is flat, 52 mm in diameter, and it doesn't move. It is situated at the very end of the lens and surrounded just by a non-rotating filter thread, 62 mm in diameter, and a mount for a hood that you get in the box with the lens.
When it comes to optical construction the lens consists of as many as 17 elements positioned in 12 groups with one element made of low dispersion SLD glass. Inside there's also a round aperture with nine diaphragm blades which can be closed down to a value of f/22 at the maximum.
Buyers get in the box with the lens: both caps, a hood, and a hard case.
