Even though many macro enthusiasts will affirm that macro should only be done using manual focus, we still expect the autofocus on these macro lenses to perform well, both in normal and in macro situations.
The following chart illustrates the focus speed for both lenses, in relation to the subject’s illumination. The subject was a black line on a white background positioned around 40cm from the camera. A K20D was used for the test. Three measurements were averaged for each point on the graph. Each lens was set at infinity, and the AF button was pressed with the camera on a tripod. The AF sound was recorded to measure the delay accurately.
Performances are very similar for the two lenses, with a minimal advantage to the Pentax. The differences almost fall within the uncertainty of the measurement, however, and only their repeatability with various EV values allow us to consider them relevant.
Focus speed outside the macro range was harder to evaluate with quantitative precision. Both lenses performed very well in this regard, with AF feeling both snappy and accurate. Small AF corrections near infinity were almost instantaneous. The lack of a focus limiter was never felt to be a hindrance with the Pentax; its AF system never strayed in the macro range when focusing on more distant subjects. Both lenses would make good choices for short telephotos. The Tamron’s focal length does make it slightly more comfortable for portraits, but the advantage is lost outside the house or studio.
Hunting is the bane of many macro photographers. Slight movements of the camera or the subject can result in long seconds lost while the lens whines all over its range, trying to lock focus.
Both of these lenses exhibited some hunting from time to time. The Tamron performed better in this respect, however. Either because of its design or its focal length (a longer focal length means a narrower depth of focus), the Pentax was more prone to hunt during our tests. The quick-shift can help in these situations, but the behaviour is still undesirable.
Neither of the lenses exhibited hunting outside the macro range.
Noise from the Tamron’s AF gears has a higher pitch than that of the Pentax. Regarding volume levels, these seemed similar between the two lenses. The lack of a precise audio recording system prevented us from quantitatively measuring eventual differences, but these would not be relevant for field use.