Tamron announced it was developing a 17-28mm f/2.8 Di III RXD lens for Sony users back in February, but only now has it made specs and pricing official.
The lens, officially christened the Tamron 17-28mm F/2.8 Di III RXD (Model A046), is described by its manufacturer as being "astonishingly small" for a full-frame, large-aperture, ultra-wide-angle zoom. That's in part thanks to to it having a 67mm diameter filter thread, despite offering an f/2.8 aperture through the entire (albeit modest) zoom range.
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It's intended as a companion to the previously launched Tamron 28-75mm f/2.8 Di III RXD (Model A036), with which it shares a development concept, to the extent that you can use the same filters and lens caps across both lenses.
Tamron has also confirmed that the model is compatible with Sony-specific focusing technology, such as the Fast Hybrid AF and Direct Manual Focus systems that feature on many current and historic models, as well as the more recently incorporated popular Eye AF feature.
Inside, 13 elements are spread over 11 groups, and this includes three aspherical elements and two low-dispersion (LD) types, as well as a single eXtra Low Dispersion (XLD) piece of glass, whose properties are said to be close to those of fluorite. Broad Band Anti Reflection (BBAR) coatings have also been used to keep transmission high and aberrations low.
Both zooming and focus are internal, which means the barrel stays the same length at all times to maintain the balance. The focusing system itself is driven by an RXD (Rapid eXtra-silent stepping Drive) stepping motor unit, which arrives with the familiar promises of high speed and accuracy, as well as "virtually noise-free" operation across both video and stills.
The barrel has been crafted with a moisture-resistant construction, which includes a seal around the lens mount area, and this protection continues to the fluorine coating on the front element, which helps to keep oil, water, dirt and fingerprints from causing problems.
Other features include a 9-bladed rounded diaphragm and support for the lens aberration correction options inside Sony's current models. The lens will also ship with a petal-shaped hood as standard to keep out extraneous light.
Tamron states that the lens will be available for $899 in the US, and it's set to go on sale from July 25. Pricing for the UK and Australia is still to be confirmed.