Nikon 70-180mm f/2.8 is 2X converter compatible
What does this mean? Well, it means that unless Tamron – the undoubted OEM of this lens just as they are the OEM of the Nikon Z 28-75mm f/2.8 – have redesigned the lens to differ in the rear mount baffles and design from their 70-180mm for Sony E-mount, a 2X converter for the Sony SHOULD be possible despite Sony’s long-standing ban on any third party 2X.
Here is the Sony rear mount.
Below is the Nikon Z-TC2 converter, which has an unusually slim intruding optical tube.
The Nikon Z mount has a register (back focus) of 16mm compared to Sony’s 18mm, which is a fairly neutral aspect as there is more room for the length of a converter barrel, but with the optical design of the Tamron and Nikon counterparts being identical the Sony rear group is 2mm closer to the bayonet mount. This should not affect how a suitably sized optical tube could be positioned.
Sony’s mount is however very much smaller in diameter than Nikon Z, a mere 46.1mm compared to 55mm. That’s nearly 9mm. so looking at the Sony rear mount photo and comparing it with the Nikon can be deceptive. That optical tube is 29mm is diameter, and the rear baffle in the Tamron E-mount would limit any intruding tube to 22mm. However, a modified Tamron E-mount with its rectangular baffle replaced (perhaps a Mark 2?) could have enough clearance with provision for the contact bezel .
We should not forget that Tamron invented the modern teleconverter with the Twin Tamron 135mm f/4.5/225mm f/7.7 (not a 2X, but a 1.7X) launched in 1958 – the lens which pretty much started Tamron’s journey to where they are now.
– David Kilpatrick