SUPERB!! I guess don't need to say more. I didn't find any weakness of this lens, color, sharpness, macro capability just excellent, if compare all this features with other 300 mm lens this is the number one. Better than Carl Zeiss Jena Sonnar 300mm f/4, Pentacon/Meyer Orestegor 300mm f/4 , Nikkor 300mm f/4.5 AI or Tair 3S.
The SP 300 F/5.6 Adaptall-2 on the other hand is a superb fixed focal length lens with excellent macro capabilities. Lens continuously focuses from infinity to 1:3.3 macro and features a built-in lens hood. Most importantly, this lens features a special spherical aberration compensator group to remove the focus group's spherical aberration when close focusing. This lens is worth the price if you need a lens for macro work and need considerable working distance from the subject for personal safety or other reasons. No other long telephoto lens ever made performs better in macro mode. It should have sold better in its day, but few photographers understood or appreciated the benefit of the spherical aberration compensator group used within this lens for close focus work.
With that said about the SP 300 F/5.6, do note that several OEM manufacturers produce 180mm to 205mm macro lenses which offer slightly better macro performance. But ask yourself, are you willing to shell out several hundred dollars for a brand new OEM lens when you can buy a SP 300 F/5.6 on eBay for anywhere from $60 to $120? Try the Tamron first. If you don't like it (and I think that you will since I love mine!) then you can always flip it on eBay.
by Michael Marcus (Adaptall-2.com )
I have a Tamron SP 300/5.6 (Model 54B), and it is one of my favourite lenses. It is relatively small, very sharp, and easy to focus, despite its relatively slow maximum aperture. I rate it as an excellent lens.
by Jim Colwell
and much more better than popular today's lens SIGMA 70-300 APO DG. After the first wonderful experience I bought one more piece to make sure if anything happen with lens I will have one more.Very nicely built, handles well very crisp and constrasty from f/8, but qulity is pretty good at wide open too.