Originally posted by larsbars I have my eyes on the tamron 70-200 f2.8. It seems from online reviews that it's pretty sharp. I am concerned about autofocus accuracy and speed.
It's fast when using the viewfinder, barely usable when using live view. You can read the comparison with the Pentax 70-200.
Originally posted by larsbars The 55-300 WR RE seems to have autofocus covered pretty well since it uses the new pulse drive system, but i'm wondering how sharp it is when compared to something like the tamron.
The 55-300 focuses faster in all lighting conditions. It's very sharp in the center, not so in the corners. It's an excellent consumer zoom, while the Tamron is a good pro zoom.
You could also consider the 60-250, it's an APS-C lens (which you can modify for full frame apparently) but it's an excellent performer, in some ways better than the Tamron, in all ways better than the 55-300.