HD Pentax-D FA 100mm F2.8 ED AW Macro

Focusing

The HD D-FA 100mm ED AW Macro does not come equipped with SDM or DC motors, relying on the screw-drive of the camera for autofocus. This had surprised us when reviewing its SMC sibling (released in 2009). It is even more astounding in 2022 and suggests that Pentax updated soley the optics and spent no time at all working on the mechanical aspects of the lens for this update. It is not dramatic for a macro lens, but still disappointing. Screw-drive tends to play poorly with live view, while macro photographers are perhaps more likely than others to use live view frequently.

Autofocus

The AF generates a significant level of noise, which can be annoying when the lens rakes through its entire focus range, but won't be overly disturbing for fine tuning between shots.

AF speed is slow when large adjustments are necessary, which is to be expected with a lens offering such a long throw. Luckily, small corrections are fast enough for everyday use. AF is very accurate and reliable even for macro work. However, we did observe some hunting when the AF system could not easily find the subject within the macro range (think about a leaf moving in the wind, fooling the AF system). In those cases, the lens can hunt all the way towards infinity before coming back and finally finding its subject after several seconds. A limiter would have removed this problem (see below). Quick-shift is a partially working solution, imperfect but globally effective.

Focus outside the macro range is in another category, being in fact surprisingly fast (more so when using the viewfinder). Small AF corrections near infinity were almost instantaneous. This lens will easily serve as a short tele for everyday use.

Virtual Focus Limiter

Version 1.70 of the K-3 III's firmware introduces a first for Pentax, a virtual focus limiter. It is available only on this camera (currently at least) and only with the HD D FA 100mm AW Macro.

By going into the camera menu (Focus Settings), it is possible to activate a virtual focus limiter. It can be set to either near distances (minimum focus distance up to approximately 70cm) or far distances (from roughly 45cm up to infinity). This simplifies AF operation when the type of scene is known beforehand. Activating the limiter has no impact on Quick Shift or manual focus, the lens can still be physically moved to any focus distance.

Live View

Live view AF (using contrast detection) can be pretty good or pretty bad. When it acquires the target in one pass, it can be reasonably fast. However, when it misses, things get worse, as it needs to scan the whole focus range before coming back to the focus point, which takes more than a second.

This shows the limitations of screw drive with live view. The HD D FA 100mm AW Macro is a worse offender than most because of its longer focus throw.

In all cases, focus has been accurate and precise. When it locks on target, that lock is accurate.

Manual Focus

Macro photographers often disregard AF completely, and depend solely on manual focus. These users will be happy to know that manual focus is extremely pleasant. The lens offers a very long throw and butter-smooth dampening. The focus ring intuitively falls under the hand and is easy to operate. Live view available on modern camera bodies allows very accurate manual focus, especially by using focus peaking. We never observed any creeping of the focus ring.

AF Speed

We tested the AF speed with a Pentax K-1 II, using both live view (contrast-detect AF) and the viewfinder (phase-detect AF). 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. The virtual focus limiter was not used to allow better comparison with other lenses.

We tested the SMC D FA 100mm Macro WR in parallel, to have a solid comparison point for the two lenses.

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

Note that 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.

In our tests, the HD version performed better than the SMC version. This shows that, despite the fact that it still uses screw-drive, the new lens carries improvements for autofocus. The differences between the two lenses are minimal when using live view, something that's not surprising considering that screw-drive isn't particularly effective with live view. Using the viewfinder, the HD version is visibly faster, and reaches almost-instant speeds beyond 1 EV (a low light level, all told). Results at closer distances will be different, and a large part of the focus throw covers this range, so these results must be taken with a grain of salt. We used 1.5 m for consistency with our other tests, but it must be understood that this is a macro lens, with a non-standard focus range.

Hunting

As mentioned before, the lens can hunt, especially with macro subjects and using live view. Hunting with the viewfinder is possible, but rare. There is an important difference between the two autofocus modes.

Verdict

It has become commonplace to criticize screw-drive AF, sometimes with good reason. Screw-drive is noisier than more modern AF motors, it does not work ideally with live view, it isn't well-suited for movies. That being said, the HD D FA 100mm Macro shows that screw-drive can still deliver fast AF with the right camera body and in the right conditions. The SMC version of the lens isn't as good, but our tests show that even this older model benefits from the improvements of newer camera bodies.