Pentax-DA 18-55mm F3.5-5.6 WR Review
In this section of the review, we will determine the speed of the autofocus mechanism in the 18-55mm WR kit lens. To achieve this, we will measure the time it takes the body to displace the focus from its closest focusing distance (9.84" or 0.25m) to its farthest focusing distance (infinity) and vice-versa. We will repeat this test 4 times and average the results.
Since this lens is fairly lightweight and compact, uses the screwdrive autofocus mechanism, and has a small focus throw, we expect the resulting times to be relatively small. The screwdrive autofocus, while very noisy, is generally seen to be quicker than Pentax's current in-lens SDM motors.
One interesting aspect to make note of is that the DA 18-55mm WR, as well as any other Pentax 18-55mm kit lens in production, uses a purely mechanical autofocus drive (using the driving motor built into the body). This aspect is unusual since all other DSLR manufacturers are offering their kit lenses with the motor drive (autofocus mechanism) built onto the lens itself. We consider that there are advantages and disadvantages to Pentax's approach. The advantages are reliability, robustness, and lower costs; while the disadvantages are the movement and noise that the screw-drive generates.
For this test, we used a K-5 body with a fully charged battery and firmware 1.14. The test scene has a luminance equivalent to 320-350 Lux which mimics indoor lighting conditions. The resulting time averages are as follows:
Average AF displacement time
|From 0.25m to infinity:||0.77s|
|From infinity to 0.25m:||0.64s|
We generally see these numbers as a worst-case scenario for locking focus via the viewfinder, though actual results will vary based on the amount of light, subject, and camera used.
As the measurements would indicate, the autofocus speeds of the DA 18-55mm WR are relatively quick and are in the general ballpark of Pentax screw-drive autofocus lenses (0.5-1.0s). The measured speed meets our expectations and we consider the overall autofocus performance of the DA 18-55mm WR to be satisfactory. If you can live with the noise that the AF in this lens produces, then you won't have any complaints about the speed.