Fast Sports Zoom Lenses for Pentax
Image Quality
An in-depth optical evaluation is outside of the scope of this article, but feel free to refer to our user reviews for more details. As far as we're concerned all three of these lenses have superb image quality and aberration control, to the point where you should not be afraid of shooting at F2.8, even at 200mm. While doing our field tests with these lenses, we got dozens of sharp, distortion-free action shots at F2.8! The Sigma had slightly soft corners at F2.8, but apart from that had no issues. Vignetting for all three lenses is negligible on Pentax DSLRs.
Bokeh
Again we see a pattern here- all three lenses boast a 9-blade aperture which delivers smooth bokeh. The Pentax and Tamron seemed to have a marginally smoother OOF area at times - perhaps due to the presence of fewer lens elements. It sure seems that all three manufacturers made image quality their priority- as it should be!
Field Test
For our field test, we took the Tamron and the Sigma to an indoor RC flying event. Our rationale for this was simple: we wanted to shoot moving objects in a low-light environment where even the K-5's great high-ISO (3200-6400) performance wouldn't let us get away with shooting wide-open or at F4. We also wanted to make sure that the autofocus was usable in low light.
Tamron 70-200mm @ F2.8, 1/250s, ISO 6400
We had a successful shoot with both lenses; they delivered sharp photographs and certainly got the job done well. This shows that they can both comfortably be used for action photography and are good at what they were designed to be able to do. Below you will find links to the sample galleries from our shoot; note that not all test photos are included.
