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| Introduction: I first acquainted myself with the Sigma 24-60mm f2.8 EX DG when I became slightly disenchanted with my Pentax DA* 16-50mm f2.8 lens. The Pentax lens required some service to the SDM motor and needed calibration to achieve proper focus at infinity-distances. Could the Sigma serve as a viable substitute? My testing revealed some pleasing results and, while not a total replacement for the Pentax, definitely performed well in most rolls necessary for a "walk-around" lens.
At a Glance: The Sigma 24-60mm f2.8 EX DG has very nice "crinkle" finish that produces a matte-black tone on the surfaces of the lens and included lens hood. This is typical for EX-series Sigmas.
The zoom and focus rings have basic gripping ridges which are adequately textured for their purpose. It should also be noted that the zoom ring is significantly broader than the focus ring on the Sigma, whereas the opposite is the case for the Pentax DA* 16-50mm. I will touch on this subject again momentarily and how it impacts handling.
The Sigma is certainly larger than a typical kit lens, yet is not so large that it is intimidating. Aiming a Pentax 16-50mm can sometimes feel as if you are wielding a small howitzer. The Sigma is about 15% shorter in length than the Pentax (83.6mm versus 99mm) but still gives the impression of being a "serious" lens. Like the DA* 16-50mm, the Sigma uses 77mm filters.
Unlike the DA* Pentax, the Sigma's lens hood does not have a pull-out window for the purpose of making adjustments to polarizing filters. For most this will have no impact on deciding to buy a lens, but it is an absent feature if the lens were meant to be a replacement for Pentax glass.
Finally, the Sigma 24-60mm f2.8 EX DG comes with a square, zippered lens bag for travel. My first thought was, "Why square?" Even with the hood reversed on the lens there is a lot of empty space unused in the bag. Still, the bag is well made and rigid enough so that it does not collapse. There is also a useful belt loop on the bag. Attaching the bag to the hip provides a sort of holster to use when swapping lenses in the field, assuming one of the lenses is not some kind of super-telephoto variety.
Handling: Perhaps the single most notable characteristic when using this Sigma lens is that its zoom and focus rings function with the opposite effects found in Pentax counterparts. Turning the zoom ring clockwise zooms in to the subject. Turning the focus ring clockwise focuses towards longer distances. Turning these rings clockwise on the Pentax DA* 16-50mm zooms away from the subject and focuses at shorter distances. While not really a strike against the Sigma, it is notable if the photographer has used all Pentax glass up to this point and then needs to pause to get used to the contrary operation. Other Sigma lenses function in the same way.
For me, the proportioning of the zoom and focus rings were just right. The zoom ring had a broader, rubberized gripping area on the lens body, making it easier to operate. Using middle and index fingers, along with my thumb, turning the zoom ring was easy. With my DA* 16-50mm and a relatively narrower zoom ring, I would frequently touch the focus ring first by accident before re-positioning my fingers on the lens body, often throwing the lens out of focus, even if just by a bit. This is also partly due to the fact that the Pentax lens has a freely moving focus ring, even when used in auto-focus mode. The Sigma, on the other hand, solidifies the movement of the focus ring, making it much harder to "bump" the focus out of alignment. In any event, photographers with large hands or gloved fingers should not find handling the Sigma 24-60mm f2.8 EX DG difficult. Everything is properly spaced.
Dampening on the zoom ring is sufficient without being too stiff. My copy of this lens makes a soft squeak during operation, but the movement is smooth and even across the full zoom range. The focus ring could use more dampening, but does not feel uncomfortably loose.
I was perplexed by the small zoom locking switch found at the 11:00 o'clock position on the base of the lens. The switch can only be enabled when the lens is set to the 24mm position. I have never found myself wanting to lock a lens in a particular zoom setting, and since the zoom ring is so well damped the lens does not exhibit any detectable zoom creep. Perhaps such an issue may arise with further use, but that has yet to be determined. If the lens could be locked at various zoom intervals, say 24mm, 35mm, 50mm, then maybe I could see the point. It seems Sigma wants this lens to be either free-range all the time or limited at its widest angle.
Image Quality: Of course, the lens is worth nothing if it can't render decent images. The Sigma 24-60mm f2.8 EX DG, like any modest-zoom range lens, has its strengths and weaknesses. In the end, however, the Sigma represents good performance and very good value considering its low average price tag circa 2010. At the time of this review, the lens has been available since mid-2004, but was discontinued about four years later.
Like many "standard" zoom lenses, the Sigma produced somewhat soft images at its widest aperture, f/2.8, when zoomed to its longest length, being 60mm. Center resolution was fair, but corner sharpness left something to be desired. The center and corner sharpness were also found to be slightly soft at shorter lengths, though it is not as noticeable. The primary strike against Sigma's image quality at f/2.8 is a sort of "mushing" of the details when viewed on a pixel-peeping level. Black-on-white shapes in test charts give the viewer an impression of looking at something through misty eyes.
The good news is that using the Sigma 24-60mm lens at any aperture from f/4 on drastically improves image quality at seemingly any zoom length. Even at its longest length using f/4 produces good center resolution and fair-to-good corner sharpness. The "misty eye" effect completely abates by f/5.6, yielding quite excellent sharpness from edge to edge of the frame.
Most lenses demonstrate a certain level of barrel distortion at their widest end, and in this case, Sigma does not break from the pack. At 24mm the distortion is rather mild. A typical sequence of brick-wall images at the various focal lengths demonstrates this. From around 35mm on there is virtually no distortion, not even perceptible pincushioning at the long end. I can see this lens being used for most situations with the exception of perhaps architecture in which the absolute minimum distortion is desired. Of course, one might also conclude that, more importantly, such a lens should not even be considered for architecture because of its limited wide angle.
Chromatic aberrations also need to be considered when choosing a lens. Luckily, the 24-60mm Sigma performs well. The weakest performance is seen at the widest angle of the lens, which is standard for most zooms. High-contrast, contra-lighting in scenes are always the culprit here. Fortunately, the levels of red/cyan fringing can be well controlled with most image editing software for this lens. Longer focal lengths set one or two stops down from the maximum produce images that practically free most distracting aberrations.
Nine rounded aperture blades produce a pleasant, smooth bokeh effect in images with limited depth-of-field. Out-of-focus highlights do not appear to have any distracting, hard-edged "rimming", which can be an effect found in images made by other lenses.
In my humble opinion, Pentax's lens coating for combating flare is second-to-none, though Sigma's own formula does a fair job against stiff competition. Yes, including strongly angled sun light or brightly back-lit objects softened the overall image contrast in tests. However, this is not a disaster for most lenses in the same class as the Sigma EX.
Other Thoughts: Throughout this review I have regularly compared the Sigma 24-60mm f2.8 EX DG to the Pentax DA* 16-50mm as a possible replacement. While I can not say the Sigma is an outright doppelgänger for the Pentax, I will give it high marks as a very fine walk-around lens. A small still-life test using both lenses at the same settings demonstrates the Pentax lens has a slight edge in local contrast, but the Sigma performs admirably well.
In some ways I would describe the two lenses as cousins. The Sigma shares Pentax's generally high construction quality and feels "just right" in the hand. Both lenses are moderately bulky, though the Sigma is slightly lighter and shorter. The Sigma feels properly balanced mounted to Pentax's larger camera bodies like the K-7. On a light body such as the K-x it may seem slightly end-heavy.
Maybe the biggest disappointment with the Sigma 24-60mm f2.8 EX DG in my experience was a moderate back-focusing issue. This echoed the very frustration I had with the DA* Pentax it was meant to replace. Making some modest changes to my DSLR's AF Adjustment settings allowed for some very nice test images.
The speed of the auto-focus mechanism is certainly no slouch, although it's definitely audible. Because the auto-focus is driven by the screw-type connection on the DSLR body it produces a somewhat unpleasant whine. Sigma's HSM technology is not present in the Pentax-iteration of the Sigma 24-60mm f2.8 EX DG. For most this fact is no deal breaker, but if you are spoiled on Pentax's silent USM drive you may wince the first few times you use the lens.
Finally, it is my opinion that the Sigma 24-60mm f2.8 EX DG can not really be judged based on its focal range. For years I got by using a 35-80mm lens mounted on my film SLR and this lens exceeds that equivalent length on my APS-cropped DSLR. The range is useful, even giving its user a little extra zoom than most kit lenses. This can be nice for portraits.
Conclusion: Considering the out-of-production status of the Sigma 24-60mm f2.8 EX DG, the lens can be hard to locate at times, but the 2010 resale value is rather affordable for a "fast" lens in this class. The original MSRP hovered around $500-$600, but today one can be had for about 50-60% of that price. Because the Sigma 24-60mm f2.8 EX DG does not have silent auto-focus or weather sealing it might not have demonstrated stratospheric value at its original price tag. However, this optically-good lens with an unusual focal range (by current standards) earns very good marks as a worthwhile and capable foundation to any photographer's glass collection.
Ratings:
8.0 - Sharpness
8.0 - Aberrations
9.0 - Bokeh
7.5 - Autofocus
9.0 - Handling
8.5 - Value
8.3 - Overall
Below are some thumbnails linked to a gallery with a few images made in downtown Lancaster, PA along with some test images, all of which were made using the Sigma 24-60mm f2.8 EX DG. The first few images are shots of the lens itself and lens bag.                   | |
