Sunday, October 12, 2014

In-Depth Review: Sigma 24-104 f4 DG OS HSM Art

Tech Specs
Focal Length: 24-105mm
Dimensions: 4.3 x 3.5 in.
Weight: 31.2oz.
Maximum Aperture: f4
Minimum Aperture: f22
Diaphragm Blades: 9
Front Element: non-rotating, non-extending
Optical arrangement: 19 elements in 14 groups
Autofocus Mechanism: Sonic Drive
Closest Focus: 17.7 in
Maximum magnification: .22x
Filter Size: 82mm

At Photokina 2012, third party photographic lens maker Sigma has reinvented its business model with a new Global Vision, whose focus is, among on other things, producing optics that can go toe-to-toe with the manufacturer products instead of serving as a poor man's alternative. To that end, Sigma has churned out a lot of drool-worthy gear in the past two years. However, there was a major hole in Sigma's revamped lineup: a fixed aperture standard zoom for full frame. Cue the lens we're reviewing here today: the Sigma 24-105 f4 DG OS HSM Art. With a long history of making fast to semi-fast fixed aperture zooms, Sigma has a lot of background in such optics and, with a new Global Vision, a stronger drive than ever to make class-leading products. So, does the 24-105 f4 OS Art deliver the goods? Well, read on to find out!

Build Quality: 5/5
The Sigma 24-105 f4 OS Art is built to the standards that were, even just a few years ago, reserved for manufacturer optics. Constructed out of Sigma's exclusive Thermally Stable Composite (TSC) material, which feels a lot like metal but whose formula is a closely-held corporate secret, the lens has a decidedly solid feel to it. In addition, the lens is inner focusing, which means that there is no moving/rotating of the front element when focusing, which is good for people who like to use polarizing filters. As for the rings, both zoom and focus rings are rubberized, highly textured, and come across as having that 'just right' balance between ease of movement and lack of slop. For some people, the dual cam inner design may be of a concern but, at least in-hand, there's no wobbling whatsoever. However, I cannot vouch for this lens when shot in harsh conditions as it not marketed as weather resistant.

AF Performance: 5/5
Focus on the Sigma 24-105 f4 OS Art is as fast, accurate, and silent thanks to Sigma's Hypersonic Motor (HSM) technology, which is the company's version of a ring type sonic-drive AF system. As for tracking, the lens had no problems with birds in flight (see samples) on the D700. As with all ring-type AF, the lens has full time manual override, which allows for instantly overriding the AF simply by turning the focus ring, no need to flip switches. In reality, the AF/MF switch is more of an AF/AF Disable switch.

 At 24mm

 At 35,mm.
 At 50mm.
 At 70mm
At 105mm
Optics: 5/5
Sharpness (Note: on DX, consider the mid frame here to be the corner)
By looking at all the test images, a pattern emerges: the Sigma 24-105 f4 OS Art is as good as it will get right out of the gate at f4 across the focal range and frame, which means that stopping down will only increase depth of field as sharpness won't noticeably improve. Needless to say, that's a very, very good thing. For nit pickers, there is some slight softening in the corner of the frame on a FF sensor when viewed at 100%. For the non-pixel peepers out there, this will be impossible to notice in real life shooting and presentation.
Stabilizer Mechanism
The Optical Stabilization (OS) feature is different than everything reviewed here in that there is no absolute way to quantify how well it works since the amount of camera shake is determined, by and large, on the inherent steadiness of the photographer's hand and shooting technique. That said, I was easily getting steady pictures of ½ second long at 105mm. Additionally, the stabilizer is absolutely silent in operation
There is some shading with the Sigma 24-105 f4 OS Art wide open at f4, with it being most pronounced at 24 and 105mm. A stop down, the shading decreases dramatically and disappears by f8. At middle focal lengths, vignetting disappears by f5.6.

There is some distortion here, but nothing out of line as for what one can reasonably expect for such a lens.  
Nil here.

While anything but a dedicated macro lens (.22x is its maximum magnification), the Sigma 24-105 f4 OS Art is still pretty good for capturing larger macro subjects, like flowers, especially with today's cameras and all of their megapixels, which allow for a lot of cropping. The above images are the full picture (albeit at a reduced resolution) with a 100% crop. 

This lens is remarkably resistant to flaring.
As is with many modern lenses, infinity is not exactly infinity here, which means that you will need to tweak focus a bit to get pinpoint stars (hint: use your live view magnification on a bright star)

With its 9-blade, rounded design, out of focus blur (bokeh) is buttery smooth.

Value: 5/5
Ah, here's the tough one as, at $900 new, the Sigma 24-105 f4 OS Art is not cheap by any means. On the other hand, when one looks at the manufacturer equivalents, this lens looks decidedly economical as the equivalents from Canon and Nikon, (Sony has no equivalent) both are a lot pricier. For both Canon and Nikon shooters, you get a dust seal at the mount on both of your camera makers' lenses (and an extra 15mm for Nikonians) but the question is this: do you plan to shoot in conditions that would warrant the rubber gasket at the mount that will add $250 and $400 to the price of the Sigma, respectively?

To put it plainly, the standard zoom lens is the most crowded segment on the market for the simple reason that such lenses are just so doggone useful. The direct competitors in the mid aperture stable from the manufacturers already addressed, there are a lot of other alternatives, too. For starters, there are the 24-70 f2.8s that are, again, made by just about everyone (Sigma makes one, too). Obviously, these lenses trade about 30mm of reach for an extra stop of aperture. The extra brightness is often offset with the cost of losing the stabilization, which often results in a wash at the checkout. The exception here: Tamron, which makes a stabilized 24-70 f2.8. Current models aside, there are out of production lenses in this focal range in both f2.8 and f4 versions, some with and other without stabilization, on the used market. Again, there's a tradeoff for that lower price: questionable support from the manufacturer. Long story short, if your old lens breaks, there may not be any parts with which to fix it, which will essentially turn your lens into an expensive paperweight.

My advice: with an AF lens (especially when paying this much), it's safer to buy new and the main consideration should be the f2.8 vs. f4.

Conclusion: 5/5
There's no doubt about it: the Sigma 24-105 OS Art is quite a lens. Sturdy build, excellent mechanics, great optics, and all at a bargain price when compared to manufacturer alternatives combine to make this lens a very attractive buy. In the end, the main consideration when buying a standard zoom comes down to this: a shorter f2.8 or a longer f4 with a stabilizer. If you decide to go with the f4 optic, there's no reason not to buy the Sigma 24-105 f4 OS Art as it really does represent a package that can cover 95% of the photographic applications of the people reading this review. Needless to say, I can't wait to see what Sigma has over the proverbial horizon!


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