Tamron has announced the release of the 70–300mm F4.5–6.3 Di III RXD, a lens deemed as ‘the world’s smallest and lightest telephoto zoom lens for Sony E-mount full-frame mirrorless cameras.’

The lens is constructed of 15 elements in 10 groups, including a low dispersion element for minimizing aberrations. Autofocus is driven by Tamron’s Rapid Extra-Silent Stepping Drive (RXD) motor technology.
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https://www.dpreview.com/news/4195388017/tamron-announces-a-compact-70-300mm-f4-5-6-3-for-sony-e-mount-cameras