Pentax 60-250mm f/4 ED IF SDM SMC DA*

SLRgear Review
August 31, 2009
by Andrew Alexander

Launched in September 2008, the Pentax 60-250mm ƒ/4 offers a focal range of 92-383mm when mounted on a Pentax dSLR camera. The lens uses the KAF2 mount designation, meaning it is compatible with both newer Pentax SDM-capable camera bodies, and older styles which only support mechanically-driven lenses. The lens offers a constant ƒ/4 aperture, and being part of Pentax's highest quality line (DA*), weather- and dust-resistant seals.

The Pentax 60-250mm ƒ/4 comes standard with a petal-shaped lens hood, lens case and tripod mount, takes 67mm filters, and is currently available for $1,300.

Sharpness
Wide-open performance for the Pentax 60-250mm is very good generally, and between 80-200mm, excellent. Our copy of this lens was slightly de-centered towards the bottom of the frame, evident at ƒ/4. At 60mm and 250mm we note some corner softness, but the sweet spot of sharpness is fairly generous at 60mm. At 250mm at ƒ/4 the lens doesn't provide tack-sharp results, but it's still exceptional: just above 2 blur units.

Between 80 and 200mm, performance is excellent at ƒ/4 - around 1.5 blur units across the frame. Stopping down to ƒ/5.6 provides tack-sharp results at 1 blur unit, and there is a similar increase in sharpness at 60mm and 250mm as well. At ƒ/8 the lens is essentially as sharp as our tests can note, at around the 1 blur unit mark (there is some statistically relevant corner softness at 60mm and 250mm, but barely worth noting).

Diffraction limiting sets in at ƒ/11, but the effect is negligible until ƒ/22 where overall sharpness begins to surpass the 2 blur unit level across all focal lengths. I'd avoid using the lens fully-stopped-down at ƒ/32, where image sharpness becomes somewhat uneven and hovers between 3 and 4 blur units.

Chromatic Aberration
The lens' resistance to chromatic aberration is commendable, showing very low levels through its range of focal lengths and apertures. The weakest point on the graph would be at 60mm. However even here the amount of maximum CA is less than 5/100ths of a percent of frame height, or very good.

Shading (''Vignetting'')
The Pentax 60-250mm ƒ/4 shows virtually no light falloff at any focal length and aperture. According to the test results, the only point where corner shading registers at all is at 200mm and 250mm at ƒ/4, where even then, the corners are less than a quarter-stop darker than the center. Nothing to write home about here.

Distortion
The 60-250mm ƒ/4 shows very low levels of distortion, and is optimized for virtually distortion-free image production at around the 70mm mark. Between 60mm and 70mm there is some slight (+0.3%) barrel distortion in the corners; above 70mm this distortion turns into pincushion distortion, and even at its highest value, above 140mm, we note only -0.2% in the corners.

Autofocus Operation
The Pentax 60-250mm ƒ/4 bridges two technologies with its autofocus system, allowing for either screw-driven operation in older bodies, or full SDM focusing with newer bodies. Our test body, the K10D, used the SDM focusing method, resulting in fairly fast performance with virtually no noise. Thanks to the fairly generous range of focusing, it took approximately 1.5 seconds to focus from infinity to close-focus. Point-to-point focusing is noticeably quicker. The lens uses Pentax's quick-shift system, allowing you to override autofocus results at any time by just turning the focus ring.

Macro
This isn't a lens you'll be buying for macro work, with a magnification rating of just 0.15x, and a minimum close-focus distance of just over a meter (over three and a half feet).

Build Quality and Handling
The Pentax 60-250mm ƒ/4 is composed of a tough plastic with an all-black matte rough finish. Being a DA*-series lens, the fit and finish of the lens is very good, and has a very ''pro'' feel to it. The more noteworthy features to this class of lens include the use of weather-resistant seals, a nine-bladed aperture and 2 ED glass elements.

There's only one switch on the lens, an AF/MF switch to enable or disable autofocus from the lens. A distance scale is provided beneath a window, showing range in both imperial and metric measurements. There's no depth-of-field scale for this lens.

The generously-wide (1 1/4'') zoom ring is rubber, textured with deep ribs. Turning the zoom ring extends the length of the lens, growing a further 2 1/4 inches. The ring itself has just the right amount of resistance to it - not too loose, not too tight, and takes about 45 degrees to go through its full range of focal lengths. Zoom creep isn't an issue with this lens.

The focus ring is also rubber but has smaller ribs, and is also generously wide at 1 1/4''. Focus distance is very generous and the ring is nicely cammed, making manual focus adjustments quite precise. There are no hard stops at either end of the focusing spectrum, just a subtle increase in resistance that lets you know you're at the end of the focusing range. The lens will focus a bit past infinity.

The included petal-shaped lens hood has a filter cutout window with a cover that detaches, allowing for the very convenient use of filters. The front element of the lens doesn't rotate during zooming or focusing, making the use of polarizers quite convenient. The lens hood reverses and mounts on the lens for easy storage.

The lens is fairly heavy (1,230g, over two and a half pounds) and the tripod mount is welcome. The tripod mount uses one of the better designs we've seen: it's unique in that just the tripod mount itself is removable, while the ring stays mounted to the lens. This means it is easier to store the tripod mount when it's not needed. The tripod mount ring has click stops every 90 degrees.

Alternatives

Pentax 50-200mm ƒ/4-5.6 ED SMC P-DA ~$230
This one's a fairly easy comparison - the 60-250mm ƒ/4 trumps the 50-200mm ƒ/4-5.6 in every category except sticker price.

Sigma 70-200mm ƒ/2.8 EX DG HSM APO ~$800
The Pentax gets a bit better competition with this lens, which while not tack-sharp at ƒ/2.8, becomes so at ƒ/4, putting it at the as-sharp-as level with the Pentax. Results for CA, light falloff and distortion are similar between the two lenses; the Sigma is two-thirds the price of the Pentax, and while not offering the extra tele and wide-angle reach, offers an extra light-gathering stop.

Tamron 70-200mm ƒ/2.8 Di LD IF Macro SP AF ~$700
The Tamron 70-200mm ƒ/2.8 is also available in the Pentax mount, although this verison of the lens uses the mechanical focusing method only. Optically, the Tamron did very well in our testing, matching the Pentax at ƒ/4 and almost the same at ƒ/2.8. Results for CA, light falloff and distortion are similarly good. Again, it's a question of the extra tele and wide-angle reach versus the extra stop, as well as the lower price.

Conclusion
Optically, the Pentax 60-250mm ƒ/4 is a winner: with excellent results for sharpness, even wide open, low amounts of CA and virtually no light falloff or distortion, it's an easy decision if you're already considering this lens and just needed to know whether or not it performed.

Sample Photos

The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.

Still Life shot

VFA target

As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.