Pentax DA* 60-250mm F4 Review

Focusing

The focus ring on the DA* 60-250mm large and well-textured. It falls easily under the hand when using the camera. The focus throw is approximately 45° and therefore rather short. The rotation does not stop when the ring reaches the maximum or minimum focus distances, but instead continues to turn with more friction and no effect on the focus position. Any opposite rotation immediately engages the focus in the other direction with no backlash. This behavior is called a soft stop, as opposed to the hard stops found on most older Pentax lenses.

Focus ring

The lens features quick-shift focus, meaning that the focus setting can be overridden at any time simply by moving the focus ring. The ring does not rotate when AF is engaged. The focus ring is well damped, feels very responsive, and is quite simply a joy to use.

The lens uses internal focusing, and the front element does not rotate. Internal focusing means that the effective focal length gets shorter when subjects are very close (the same applies to any lens with internal focusing).

The lens features two autofocus systems. On older bodies (predating the K10D), AF is driven by the traditional screwdrive shaft. On newer bodies, Pentax's in-lens Silent Drive Motor (SDM) is used, providing near-silent AF.  In this review, we do not compare the speeds of the two systems, though we will say that Pentax's SDM motors are not known for their speed.

The SDM does feel accurate and responsive, however. A subtle whirring noise can be heard when listening closely in a silent environment, but for all practical matters the autofocus system is silent.  It is therefore a big improvement over the dated screwdrive system.

Pentax's SDM motors have suffered from poor reliablity in the past.  Fortunately, according to a survey we conducted in 2012, the SDM system on the DA* 60-250mm proved to be quite reliable.  Only about 5% of 60-250mm users reported an SDM failure; failure rates for other lenses, such as the DA* 16-50mm, were as high as 30%. Recent reports from users and from Pentax engineers suggest that the SDM issues were resolved in late 2012, however.

Considering the likely uses of this lens, AF speed is of paramount importance. The following chart illustrates the focus speed in relation to the subject’s illumination. The subject was a black and white shape with sharp transitions (the center spot of the resolution target presented later in this review) positioned around 150cm from the camera. The lens was set at 60 and 250 mm. A K20D and a K-5 were used for the test. Three measurements were averaged for each point on the graph. The lens was set at infinity, and the AF button was pressed with the camera on a tripod. The AF confirmation beep was recorded to measure the delay accurately.

Focusing

The lens had a clear advantage with the Pentax K-5 compared to the older K20D, especially in low light. Higher light levels show a smaller difference between the two cameras. Interestingly, the focus is faster at the long end than at 60mm. In near darkness, AF is somewhat slow. It catches up quite fast when light levels increase, stabilizing below one second in good conditions (it must be noted that 5 EV is still pretty dim, a bright sunlit day is between 14 and 18 EV).

Micro-adjustments are of course faster. When a rough focus has been achieved prior to the shot, the AF is too fast to be measured with precision.

Hunting

Hunting occurs when a camera and lens system fails to lock focus, and move the AF point back and forth without acquiring a lock. It can occur with any lens under the right circumstances.

The DA* 60-250 exhibited no hunting during our tests. It moved quickly and steadily towards the correct focus point, flawlessly and every time. Even in low light, when focus is slower, it is still accurate.

Verdict

The focus speed of the DA* 60-250 is good and micro-adjustments are quick thanks to the silent drive motor.  The lens' autofocus may feel sluggish at times due to long focusing throw, and it is slow to focus in very low light, but it's still acceptable. In everyday use, autofocus feels responsive and trustworthy.  There are faster-focusing lenses out there, such as the Sigma 70-200mm, so for those interested in the fastest speed possible, a different lens may be appropriate.


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