I had a PM requesting a comparison of the focusing speed between these two lenses... Using my patented (well no not really) record the lens focusing and compare the sound waveforms visually in
Audacity technique, I got some results for ya...
First methodology...
I used my cell phone to record these lenses focusing from their closest focusing stop to a point approx. 15' away, so I'm not focusing to infinity here, but most of the way there for the both lenses. I would prefer to compare the time it takes for worst case focus travel time from close to infinity, but I didn't have a target with a clear shot out my bedroom window, and conditions dictated that this is the data you're gonna get for now
. Both lenses were mounted on my K20D with fairly fresh batteries in it
(body and grip).
In Audacity, I cropped away the silence on either end of the focus cycle - you can see the 50-135 is startlingly quiet, and this is an unfair volume comparison as this recording was made with my phone (the recording device here)
touching the lens body whereas the Tamron recording was probably made at a distance of about 5 inches... I would speculate the loudest part of the SDM focusing - the spikes at each end of the cycle is the clutch mechanism engaging and later disengaging but I really have no idea.
Here's a screenshot of the waveforms...
So, a second for the DA* and just under 0.7 sec. for the Tamron.
If anyone can send me a recording of their HSM Sigma 70-200 from close focus to infinity, I'll redo my recordings to cover that focus range too, and repost that info..