My detailed thoughts on the Tamron 20-40mm F2.8 are covered in a blog post where I travelled with both this lens, and the Tamron 35-150mm F2-2.8. I created this page to make it easier for people and search engines to find my detailed post that doesn't have such a specific title!
This was a great lens and easily one I can recommend to photographers. Very sharp. Very good AF performance. Very compact form factor and delivers professional results.
Full details here in my November 2023 Tamron zoom-lens feature:
https://ewenbell.com/blog/Tamron_Got_It_Covered
Also check out my photo essay using this lens and the 35-150mm posted here:
https://ewenbell.com/editorial/Fire+and+Water
– Ewen