HD Pentax-DA Fish-eye 10-17mm F3.5-4.5

Focusing

Despite being a "recent" lens, the HD DA 10-17mm does not feature an upgrade regarding autofocus. As such, it relies on the older screw-drive AF system. This means the 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 not silent but the noise is not overly disturbing. It can still be heard at times. The lens uses internal focusing and does not change length when changing focus distance. The focus ring rotates when using AF, however.

The AF is generally accurate and responsive. The long depth of field associated with extreme wide angles help with this.

The lens allows for quick-shift manual override of the autofocus at all times.

Live View

Again thanks to the wide depth of field, AF using live view does not struggle, even though the lens uses screw-drive AF. In use, it feels responsive and reliable.

Manual Focus

Manual focus with the fisheye works well enough. The ring is, sadly, completely lifeless, with no feedback for the user. This is not unexpected for a consumer-grade AF lens, but we always prefer lenses with more feel in this regard. The focus ring rotates over a 90° throw, with most of the throw covering the range from 0.14 to 0.5 meters

AF Speed

Since the lens is APS-C, we tested the AF speed with a Pentax K-3, 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 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.

Using the viewfinder, the 10-17mm offers impressive AF speeds, even in very low light. As light levels increase, it would be difficult to ask for faster AF than what this lens is capable of.

Using live view, the lens is much slower until about 2 EV. Before that, part of the delay comes from the AF assist system which appears to take a moment to wake up. This behavior was not observed using the viewfinder.

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

Hunting

We experienced no occurrences of hunting with the 10-17mm 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 DA 10-17mm offers superb AF speeds when using the viewfinder, and acceptable results in live view, except in very low light. Manual focus is accurate but the ring feels lifeless.

Autofocus is certainly one of the lens's strong suits.