The Tamron 28-200mm f2.8-5.6 Di III RXD (model A071) is an all-in-one zoom designed for Sony’s Alpha mirrorless cameras and corrected for full-frame sensors. Announced in June 2020, it is a more affordable and lightweight alternative to carrying Tamron’s 28-75mm f2.8 Di III plus 70-180mm f2.8 Di III zoom lenses although you give up on a constant f2.8 focal ratio – and probably some image quality.
Physically, the 28-200mm f2.8-5.6 Di III is a little smaller and 200g / 7 oz. lighter than the alternative from Sony, the FE 24-240mm f3.5-6.3 OSS, and both lenses extend while zooming. The new Tamron has no optical stabilization and relies solely on the image stabilization provided by the Sony Alpha mirrorless cameras while the Sony FE 24-240mm f3.5-6.3 OSS has optical image stabilization.
The Tamron 28-200mm f2.8-5.6 Di III should become available end of June. Ahead of my full review I’ve compared the new lens and the alternative from Sony based on the information so far available from Tamron. PS – if you’re interested in the other full-frame zoom lenses for E-mount in Tamron’s line-up check out my in-depth reviews: Tamron 17-28mm f2.8 Di III RXD review / Tamron 28-75mm f2.8 Di III RXD review / Tamron 70-180mm f2.8 Di III VXD.
Facts from the catalog
Let’s compare the new Tamron 28-200mm f2.8-5.6 Di III to the Sony FE 24-240mm f3.5-6.3 OSS (“Sony” for short). As usual I’ve rated the features with a [+] (or [++]), when it’s better than average or even state of the art, a  if it’s standard or just average, and [-] if there’s a disadvantage.
Size (diameter x length): At 74 x 117mm (2.9 x 4.6in.) without lens hood the new Tamron is a pretty small lens, even a bit slimmer than the Sony at 81 x 119mm (3.2 x 4.7in). Both lenses extend when zoomed to the longest focal length. [+]
Weight: 575g (20.3 oz.) without lens hood. Complementing the new zoom lens with Tamron’s 17-28mm f2.8 Di III to cover the very wide end makes for a lightweight combo of only 1kg (2.2 lb.) covering a 12x zoom range. The Sony is 780g (27.5 oz.). [+]
Optics: The Tamron 28-200mm f2.8-5.6 Di III employs 18 elements in 14 groups including 3 special dispersion elements and 4 aspherical elements. The Sony has 17 elements in 12 groups including 5 aspherical elements. [+]
Focal ratio and coverage: The Tamron is 2/3 of a stop brighter than the Sony at the short end and 1/3 brighter at the long end. So this is a slight plus for the Tamron in light gathering power and subject isolation. But the 10x zoom-range of the Sony has the upper hand over the 7.1x coverage of the new Tamron. This gives the Sony a 9 degrees wider angle of view on the short end (84 degrees vs. 75 degrees) plus 20% more reach on the long end compared to the Tamron. 
Contrast and resolution: Comparing the MTF charts of both lenses is a bit tricky as Sony crammed both the wide open performance (green lines) and performance at f8.0 (red lines) into the same chart. Looking closely the Tamron shows less astigmatism on the wide end than the Sony with comparable overall contrast and better resolution towards the full-frame corner. At the long end the Tamron also shows some astigmatism but not nearly as much as the Sony and again the Tamron should be a bit sharper. How clearly this shows in real life shooting will be interesting to see once I have a chance to test both lenses side by side. [+]
Closest focus distance is 0.19m (0.6ft.) with a magnification of 1:3.1 and a working distance of only 4.5 cm (1.8in.) at 28mm focal length. At 200mm focal length maximum magnification is 1:3.8 which is still quite good and results in a much more usable working distance of around 0.66m (2.2ft.). The Sony achieves a maximum magnification of 1:3.7. [+]
Filter-thread: The Tamron 28-200mm f2.8-5.6 Di III shares the same 67mm filter-thread with the 17-28mm f2.8 Di III, 28-75mm f2.8 Di III, and 70-180mm f2.8 Di III which is very convenient – and saves costs. The Sony takes 72mm filters. [+]
Image stabilization: The new Tamron does not offer optical stabilization. The lens solely relies on the sensor-based image stabilization of the Sony Alpha mirrorless cameras. The Sony zoom lens has optical image stabilization built in which works together with the sensor-based image stabilization of a Sony Alpha body. 
Auto focus: Yes, with built-in stepping motor drive. Manual-focus override is by simply turning the dedicated focus ring. The focus ring probably has a variable gearing (like Tamron’s other f2.8 zooms for E-mount) which allows for very precise manual focus when turned slowly but cannot be switched to linear gearing. Which makes smooth focus pulling for videographers almost impossible. [+]
Covers full frame sensors or smaller. Same with the Sony. [+]
Price: The lens comes at a recommended retail price of 869 EUR (incl. 19% VAT) / 729 USD / 799 GBP. The Sony currently goes for 780 EUR / 1050 USD / 690 GBP. So the new Tamron seems a bit overpriced in EUR and GBP considering its narrower zoom-range and missing optical stabilization in comparison to the Sony. But I think we’ll be seeing street prices for the Tamron that are considerably below the RRP. 
The lens comes without a pouch but the lens hood is included and is reversible for transport. Same for the Sony. 
Aperture ring and other control elements: The new Tamron has a zoom-lock but neither the Tamron nor the Sony have an aperture ring or a AF/MF switch. 
Sealing: yes, a rubber grommet at the lens-mount plus further special weather-sealing throughout the construction, just like the Sony. But the Tamron has fluorine-coating on the front element to repel water, dust, and dirt and make cleaning easier – a feature the Sony misses. [+]
The score in the “features-department” is 0[-]/5/9[+] which makes the new Tamron 28-200mm f2.8-5.6 Di III look like a well balanced design. On the plus side is its small size and low weight together with a large f2.8 focal ratio on the short end plus a very useful magnification in close-up shooting. And if the MTF-charts are any indication the Tamron probably outperforms the alternative from Sony. The missing optical image stabilization might not be too big a drawback as the stabilization of Sony mirrorless bodies is pretty effective. But you might not like that the lens starts at 28mm on the short end. 24mm focal length is sometimes the ticket to get the framing right in wide landscape or architecture shots. Here the Sony FE 24-240mm f3.5-6.3 OSS has a clear advantage with its 10x zoom range.
Keep your eyes peeled for my first tests of the optical qualities of Tamron’s 28-200mm f2.8-5.6 Di III once I can get my hands on a copy.Check prices at Amazon, B&H, Adorama, eBay or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!