J. Kuehn
Summary: solid, well constructed, bright, quick to focus, spectacular vibration compensation, and fairly compact compared to some competitors, BUT out-of-the-box autofocus is a serious problem requiring calibration. For that reason Im rating the lens as follows: Before Calibration: 2/5 stars (poor image quality out of the box) After Calibration: 4+/5 stars (excellent image quality and a great value) Overall Rating: 3/5 stars (for requiring user calibration) Tamrons lens dock (The Tap-In-Console) allows for high level control over the lenss autofocus settings. Using a high quality focus target, it took about an hour to estimate the autofocus fine-tuning corrections needed for the lenss autofocus. The measurements had to be conducted at 24mm, 35mm, 50mm, & 70mm for a target that is 1.25ft, 3ft, and 30+ft -- a dozen corrections with 10-20 test shots required per correction (a total of 100-200 test shots with camera adjustments for each test). The whole measurement process took me a little over an hour. The measured AF-FT corrections ranged from -12 to +14 and depended on the focal length and distance -- dont expect to enter a single value into your camera to fix the AF issues. Using the Tap-In-Console (not included with the lens I bought, but bundled by some sellers) and software (downloaded), you can quickly enter the dozen corrections and save them to the lens (you can also update the lens firmware and modify some of the other lens parameters). Once the measurements were completed, the process of entering the new settings took just a couple minutes, measuring the corrections was the time consuming part. Not difficult. Just time consuming. While Im still testing, now that the lens is calibrated, my early impression is that Im pretty happy with the image quality and would tentatively rate it 4+/5 stars after the calibration. So, if you dont mind having to calibrate the autofocus for the lens, read this as a 4+/5 review and a *very* good value for an f/2.8 24-70mm once calibrated. If youre counting on the lens to have tack-sharp autofocus out of the box, read this as a 2/5 review -- seriously, just expect youll have to calibrate it. Overall, because of the necessity to calibrate, the out of the box experience (including ordering and waiting for the arrival of a Tap-In-Console) warrants an overall rating of 3/5 stars.