I wanted to experiment with different wide angle lenses for IR photography other than the Pentax-M 20mm f4 lens I almost exclusively used before. Last time I tried the Flektogon 35mm f2.8 with good results, and I decided to try my widest manual focus lens - the Tamron SP 17mm f3.5. As it turned out, it wasn't bad at all. I was afraid I could not get infinity focus, but with aperture set at f8-f11, it was fine. What I really should have done, is try the Canon FD 20mm f4 against the Pentax-M 20mm f4, but there is always the next time.
The Tamron SP 17mm f3.5 is not as sharp the Pentax-M 20mm f4, especially at the edges, but it's a much wider angle therefore not a fair comparison.
The Hug Me Tree 2013 - Canon 20D IR & Tamron SP 17mm f3.5 Adaptall. Click for larger.
Grange Park - Canon 20D IR & Tamron SP 17mm f3.5 Adaptall.
Tree outside Umbra building - Canon 20D IR & Tamron SP 17mm f3.5 Adaptall.