SMC Pentax-FA 50mm F1.4

Focusing

The FA 50mm was introduced in 1991, at a time when all autofocus was done via screw-drive. This means AF will not be silent and is not likely to perform as well in live view. On the other hand, it makes the lens fully compatible with older camera bodies.

Autofocus

The AF's noise levels are kept well under control. The lens is certainly not silent and emits a high-pitched sound as it focuses, but the noise level is not distractive. The lens gets slightly longer as it focuses towards closer distances.

The AF is generally accurate and responsive. The large maximum aperture helps the focus system getting enough light to operate.

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

Live View

Older lenses are not expected to perform well in live view. However, the fast maximum aperture of the FA 50mm gives the AF system plenty of light to operate and the lens is actually very reliable when used in live view. There is no hint of hunting and no hesitation when focusing.

Manual Focus

Manual focus with the 50mm is adequate .The FA lens's ring is easy to find, being placed at the front of the lens. Its rubbery texture makes it easy to grip. However, the praise stops there. The focus ring is lifeless, as was often the case with film-era AF lenses. The throw is long, at approximately 145°.

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.

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.

The FA 50mm is a pleasant surprise when using live view. It is rare to see an older, screw-drive lens reaching such speeds. With the viewfinder the results aren't as good: the lens is quite slow in low light, although it does reach acceptable speeds as the light level increases.

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

Hunting

We experienced no occurrences of hunting with the 50mm during our tests. It is probably possible to cause hunting in the right circumstances but it is not something that was observed.

Verdict

The FA 50mm F1.4 focuses quickly when light levels are good, and remains fast using live view under low light conditions. Its AF system is reliable if not always the fastest.