HD Pentax-DA 35mm F2.8 Limited Macro

Focusing

The DA 35mm macro does not feature the newest silent SDM or DC motors. Instead, it relies on the screw-drive of the camera for autofocus. A screw-drive means that the lens is compatible with every legacy camera model. Screw-drive focusing is considerably louder than in-lens focusing, however, and less adapted to live-view focusing.

Autofocus

The AF delivers a moderate amount of noise in most situations. It compares well with other light primes such as the DA Limiteds. The only situation where the AF noise can be bothersome is when the lens rakes through the whole range, a somewhat tedious process because of the long focus throw. The following video illustrates an extreme example of hunting, where the lens is set at infinity and tries to lock focus on a close black surface in low light.

The AF is very accurate, something that is paramount for a macro lens.  With the latest Pentax bodies, focus errors during our tests were rare. They occurred mostly when trying to perform close focusing handheld, in which case user movements are as likely to blame as the lens itself.

AF speed is not particularly impressive. This is easily understood: a macro lens usually has a long throw, especially on the short distance range. This ensures that small adjustments are possible and that macro images will turn out just as expected. However, it also means that the AF system has a long way to go from one end of the range to the other. Small AF corrections were faster than large movements, and never felt sluggish, especially outside the macro range. When used as a normal lens, AF is comparable with regular (non-macro) lenses.

As with any macro lens, hunting is likely to occur if the lens misses a close subjects, and rakes through the whole range before slowly coming back to its starting point. The lens lacks any kind of focus limiter which could help avoid this type of hunting. On the other hand, it does feature Pentax's Quick Shift focus clutch. When the lens misses the subject, the simplest solution is to immediately turn the focus ring towards the desired focus distance, and either finish focus manually, or let the camera fine-tune the adjustment.

Note that the Pentax K-3 (launched in 2015) and all newer Pentax DSLRs feature a more powerful screw-drive motor compared to prior bodies.  This motor speeds up focusing speeds by up to 50%, but it may make focusing more noisy.

Live View

Focus speed is visibly slower when using live view instead of the viewfinder. Screw-drive lenses tend to perform poorly with live view, so the AF performance of the lens in that case is actually better than average. The same level of accuracy was obtained with live view than with the viewfinder.  However, in low light the lens tends to overshoot in live view and move the AF point far beyond the target, before correcting back. This results in an increased focus delay and a high level of noise. By comparison, viewfinder AF tends to make several micro-adjustments in low light, a technique both faster and much quieter.

The following video shows the same situation as above, with contrast detection AF being used this time.

Manual Focus

Manual focus is very important on a macro lens, even one with autofocus. Some macro shooters refuse to rely on AF since it is often necessary to adjust the focal point with more precision than what the AF system offers.

We are happy to report that manual focus on the DA 35mm macro is very pleasant. This is generally the case with both Limiteds and macro lenses, and our test unit does not disappoint. It offers a long throw (160°, a bit shy of a half-turn)  which makes manual focus easier than with many modern lenses. This is actually shorter than what is found on other lenses (for reference, the DFA 100mm macro WR has a 270° throw!). Given the deeper field of view granted by the wider focal length, an excellent level of control is still possible. When we used it, we never felt any lack of accuracy with the focus ring. It must be emphasized that 160° is still much more than average.

There is a good level of dampening on the focus ring. The movement of the ring feels very smooth ("buttery" comes to mind), a fact highlighted even more when comparing with the rough movement of the DA L 35mm F2.4. This is both expected and commendable. The ring is perfectly positioned and easily falls under the hand. We never observed any creeping of the focus ring, nor would we expect any given the size and weight. The lens extends by a significant amount when focusing at close distances, as can be seen below.

AF Speed

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 one meter in front of the camera. We used the central focus point. We usually set the lens at infinity before testing. However, in this case, since the throw is much longer towards shorter distances, the lens was set at the closest distance 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. To give an idea of performances from infinity to around 1 meter, we took one measurement at a little over 4 EV of ambient light (shown on the graph).

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

This chart illustrates how performances can vary with illumination. For very low light levels, focus is slow, which is to be expected. Up until about 3 EV, phase-detection AF (via the viewfinder) is visibly faster than contrast-detection AF (with live view). This is to be expected with a screw-drive lens. Speed improves for both methods when light levels get higher than 2 EV. With higher light levels (remember that 5 EV is reached by using one 65W light bulb in the ceiling, no more), speeds get very respectable, if not blazingly fast. At those levels, live view gets almost as fast as the viewfinder.

What is impressive is the speed can go from infinity to 1 meter. The focus speed is more than twice as fast as the other way around. This indicates that when the lens is used as a "normal" lens, outside of the macro range, it will focus much faster, on par with other lenses of the same type.

Note that at very low light levels, focus can be erratic and unreliable at times. This will depend strongly on the shape and contrast of the subject.

Verdict

The DA 35mm macro's AF speed isn't particularly fast. This is not a surprise considering how we test AF. Small adjustments are much faster, however hunting can occur during close focusing, if the lens misses the subject. Accuracy is very high. The level of noise is adequate for a screw-drive lens.

In summary, while it isn't ground-breaking, the lens' AF performance is within our expectations for a macro lens. Manual focus is a joy to use, and the long throw ensures a high level of accuracy.