HD Pentax-D FA 70-210mm F4 ED SDM WR

Focusing

The D FA 70-210mm uses a modern autofocus system, with the most recent incarnation of Pentax’s SDM motor. The lens lacks the mechanical screw-drive coupling required for use with older camera bodies, but will autofocus with cameras dating from the K10D (2006) or more recent. As mentioned earlier, though, the aperture won't work with cameras older than the K-50 (2013).

Autofocus

The AF system is almost inaudible even in a silent environment. This is one of the best incarnations of a silent AF drive we have seen. Focusing is internal and the length of the lens remains constant. The focus ring does not rotate as the lens focuses, and the front element does not rotate.

The AF is generally accurate and responsive. The impression is that of a particularly decisive system.

The lens allows quick-shift for manual AF override at any moment.

The lens includes two switches on the side. The first is an AF-MF toggle, a somewhat redundant feature since all Pentax cameras provide a similar control near the lens mount on the camera body. The second switch controls the limiter. When the focus distance is set above 2m and the switch is activated, focus will be limited from 2m to infinity. In the other mode the limit is set from 0.95m to 2m. In use, we never observed that the limiter was actually required, but it is certainly a nice-to-have.

Live View

Live view focusing feels slightly less responsive, but just as decisive as using the viewfinder.

Manual Focus

Manual focus with the 70-210mm is better than expected for an AF lens. The focus ring has a surprisingly good level of friction and strong dampening. There is no backlash when reversing the direction. The ring has a 180° throw, a high value for an AF lens.

The lens exceeds our expectations regarding manual focus.

AF Speed

We tested the AF speed with a Pentax K-1 II, using both Live View's Contrast-Detect Autofocus (CDAF) and the standard Phase-Detect Autofocus (PDAF, through the viewfinder). The subject was a black cross on a white background, about 1.5 meters in front of the camera. We used the central focus point. We set the lens at infinity before each test, and three measurements were averaged for each data point. Measurements were performed by recording the AF noise, at various levels of ambient light.

Pentax released an updated firmware for the K-1 II to improve performances with the 70-210mm. Our tests were performed with this firmware (version 1.04).

For reference, the Pentax K-1 II's autofocus sensor is rated for ambient light levels as low as -3 EV.

Also, about 5 EV corresponds roughly to a small room lit with a 60 W bulb, and a sunny day corresponds to 16 EV, and a moonlit night to -2 EV.

The difference between using the viewfinder and using live view is the obvious takeaway. Using PDAF (via the viewfinder), the 70-210mm is almost astoundingly fast in our test. The results are impressive even below 1 EV. For ambiant levels above 2 EV, AF speed reaches its peak performance, which is below 0.4 seconds. this means the combination of a K-1 II (with up to date firmware) and the D FA 70-210mm becomes almost insensitive to ambiant light level, as long as they are above around 2.5 EV.

There is an important decrease in performance when using CDAF (via live view). Consistent results were verified by repeating the test, since it is not usual with a modern lens to see such a difference between PDAF and CDAF. We must stress that in other conditions, outside of our controlled test setup, the 70-210mm offered better results with live view.

Supporting these observations, we confirm that, when testing outside at night under the illumination of street lamps, the AF system struggled and sometimes failed to lock focus when using live view, but locked accurately and extremely fast when using the viewfinder.

It must also be noted that, at the lowest light level tested (around 0.6 EV), the camera used its AF assist beam, and this appeared to improve the results. For instance, the live view curve does not follow the viewfinder curve at this light level. If the camera had elected to use the AF assist beam at higher light levels, CDAF would have delivered better results.

Remember that actual speeds will vary greatly with the subject and lighting conditions.

Hunting

We experienced almost no occurrences of hunting with the 70-210mm during our tests. The decisiveness of the AF is one of the highlights during our tests.

Verdict

The Pentax D FA 70-210mm's AF speed can be almost incredibly swift using the viewfinder, even in low light. It remains usable with live view, but is certainly not as fast.