The Pentax smc FA 50mm F1.4 is a pretty well-built lens, which (no doubt helped by its compact dimensions) feels distinctly 'dense', and as solidly built as any other lens in its class. The mount is metal, and the barrel constructed of high-quality plastics with a totally smooth rubber focus ring. Unlike its counterparts from Canon, Nikon and Sony, the front element is hardly recessed at all from the filter thread, suggesting that it may be more susceptible to flare caused by stray light (and strong side light in particular). As is typical for lenses of this type, the entire optical assembly moves backwards and forwards as a unit by about 8mm for focusing.
On the camera
The 50mm F1.4 is small and compact, making it a beautifully discrete companion to Pentax's DSLRs (especially the diminutive K2000 / K-m). The focus ring falls readily to hand, however unlike Pentax's newer designs, the 50mm does not feature their 'Quick Shift' mechanism which allows manual tweaking of focus when the camera is set to AF, instead you have to flick the switch on the camera body to change modes.
The traditionally-placed aperture ring is relatively broad and very positive in action, unfortunately it's only fully useable on older Pentax 35mm SLRs, and DSLRR bodies lack the mechanical coupling on the lens mount necessary to detect the set aperture. This means that normal auto exposure modes are unavailable, and while manual mode can be made to work after a fashion (using the 'green button' beside the shutter release to meter and set the recommended shutter speed), it's still pretty clunky (there's no viewfinder readout of the set aperture, for example). It's probably easiest to leave the lens set to 'A', and use the camera body's controls instead.
The 50mm F1.4 relies on the body’s built-in AF motor for focusing, which makes it slightly noisy (although this is entirely dependent upon the camera body) and certainly more obtrusive than ultrasonic motor-equipped lenses such as the Sigma 50mm F1.4 EX DG HSM. Overall, autofocus was fast and positive on the K20D we used for testing, although the camera could struggle for absolute accuracy when shooting with the lens at maximum aperture. As always, it must also be noted that focus speed and accuracy is dependent upon a number of variables, including the camera body used, subject contrast, and light levels.
Lens body elements
Reported aperture vs focal length
This lens allows an aperture range from F1.4 to F22 to be selected.