SMC Pentax-FA 43mm F1.9 Limited Review

Focusing

Like all film-era lenses, the FA 43mm Limited uses screw-drive for autofocus. The good news is that this makes the lens compatible with older camera bodies; however AF will not be silent.

Autofocus

The AF generates a low level of noise: the minuscule size certainly helps. The lens' shaft becomes marginally longer as it focuses towards closer distances.

The AF is generally accurate, responsive and decisive. It is fast, a good illustration of what can be obtained when screw-drive is done well.

Since this is an FA lens, there is sadly no provision for quick-shift.

Live View

Focus speed when using live view is generally not impressive with older, screw-drive lenses. Just like the FA 31mm, the 43mm exceeds expectations in this regard. Contrast AF is both responsive and accurate. There is no hesitation; the lens goes directly to the correct AF point. Subjectively, the lens appears just as fast with live view as it does with the viewfinder. The accuracy of the AF system using live view is high, with no hunting and no missed shots with static subjects. Considering the age of the design, this is particularly impressive.

Manual Focus

Like the other Limited lenses, the FA 43mm retains some of the feel of older, manual lenses: the focus ring is adequately dampened, accurate and with good feedback. It is not quite as smooth as a fully manual lens, but comes close. This is no surprise and is on par with what we have come to expect from FA Limited lenses. Manual focus is easy to perform with good accuracy. The ring's throw is 150°.

AF Speed

We tested the AF speed with a Pentax K-1, using both live view and the standard PDAF (Phase Detection AF, 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.

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

The chart illustrates that, in good light, the lens can achieve focus in a fraction of a second. In particular, when light levels are high, live view delivers almost-instant focus lock. Note that 5 EV corresponds roughly to a small room lit with a 60 W bulb, a sunny day corresponds to 16 EV, and a moonlit night to -2 EV. At lower light levels, the focus speed is still acceptable, particularly via the viewfinder. Live view did not struggle to lock focus but took longer.

The sweet spot is at around 2 EV, where both AF systems become very close and where AF speeds drop below a half-second. The small size of the lens certainly helps the screw-drive system to move optical elements around and achieve focus quickly.

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

Hunting

We experienced no occurrences of hunting with the 43mm during our tests. It is probably possible to cause hunting in the right circumstances but it is not something that was observed.

Verdict

The Pentax FA 43mm Limited delivers fast and reliable AF, both in live view and with the viewfinder. AF can become almost-instantaneous when light levels are good. Manual focus is pleasant and easy thanks to the well-dampened focus ring. The lack of quick-shift is no surprise but would have been a nice bonus.