Sigma 18-35mm F1.8 DC HSM "Art"
Construction and Handling
In this section we scrutinize every aspect of the physical construction of this lens. Why? Well, that way you can appreciate exactly what to expect should you decide to commit your hard earned money on the Sigma 18-35 F1.8 zoom. And for the lens porn.
Front Element and Front Lens Cap
The front element of the 18-35 is free of any markings, which is unlike many Pentax lenses that have the lens name or at least the filter size engraved on the face.
Protected by a Sigma-branded pinch-type cap, the filter threading of the lens is 72mm. This is important to note for those of you who use lots of filters and expect to share them across several lenses - up until the official announcement of the HD Pentax-DA 16-85mm F3.5-5.6 ED DC WR in October 2014, there were no lenses in the current Pentax line-up that featured that filter size. Plenty of 67's and 77's, but not a single 72mm threading.
Additionally, we wanted to point out an interesting observation regarding cleaning the glass (as some accidental finger prints may have appeared on the front lens during our time with it). While using a lenspen to clean the front objective, the lack of Pentax's Super Protect coating became immediately apparent. Hard to explain in words, it was merely a difference in "smoothness" between the SP coated lenses and the Sigma 18-35 when rubbing the lenspen across them. On the Pentax lenses, the pen seemed to just glide across while the Sigma seemed to exhibit a lot more friction, "sticking" a bit more. At the end of the day, it's not a huge issue and won't have a direct impact on the lens's image quality output, but it was a difference we immediately noticed. We suspect that should you be in inclement conditions (lack of weather sealing aside), the Sigma may be a bit more prone to flecks of dust or small water droplets sticking to the glass as compared to Pentax's SP treated lenses.
Lens Body
The first thing that comes to mind when you hold this lens is its sheer size, but we'll touch on that a bit more a few sections down comparing this "Art" lens to other lenses.
Upon closer inspection the next thing you notice is simply how beautiful the lens is. As Pentaxians, we have come to appreciate premium lenses that not only perform well, but also look the part. The Limited lens series, both FA and DA, certainly satisfy both criteria.
The Sigma 18-35 "Art," however, takes a different approach than the Leica/Zeiss-esque 100% metallic build we've come to love. Instead, it boasts a lens that is beautifully crafted and well made through a combination of machined aluminum and Sigma's proprietary TSC, or Thermally Stable Composites, promising minimal variations in physical size (expanding/contracting) due to temperature differences.
Simple and sleek, the body doesn't boast any lavish designs or loud colors. Also, as stated in the introduction of this review, the Sigma 18-35 is a member of the "Art" series of lenses from Sigma. This is evident by the silver badge emblazoned on the lens barrel:
In case you weren't aware, for the "Contemporary" and "Sports" lenses within Sigma's Global Vision line, that same badge would instead display a "C" or "S," respectively.
To the right of the filter window and the engraved specs of the lens (focal length, aperture, and filter thread size), the SIGMA logo is in bold white, with a very subdued serial number etched into the barrel. It may not look like it here, but the etching is so subtle that at first we thought it was a pencil mark/scribble (as it's that same shade of graphite). Also, it looks much smaller in person than how it appears in the crop below:
Lastly, there is a switch on the side of the barrel for activating and deactivating the in-lens autofocus, but we will discuss that in a bit more detail on the autofocus page of this review.
Size Compared to Similar Lenses
The Sigma 18-35 can be considered a "bag of primes" because of its constant F1.8 aperture. But, because it is a zoom covering the standard range, we wanted to see how it fared against not only primes, but standard zooms as well. As such, we placed it between three other lenses that are undoubtedly going to be compared against when considering this Sigma zoom. The fourth lens we included in this size comparison is the Sigma 8-16mm in case you may be considering the two Sigmas as a set of sequential zooms.
From left to right in the following animated .gif is the Sigma 8-16mm F4.5-5.6, FA 31mm F1.8 Limited, Sigma 18-35mm F1.8, HD 20-40mm F2.8-4 Limited, and the DA* 16-50mm F2.8. The two lenses on the left have permanent hoods, however the next three are shown with and without their detachable lens hoods.
As you can see, the Sigma is much larger than all the other lenses, especially the two Limited lenses. The HD 20-40 especially surprised us with how much smaller it was. To demonstrate just what the differences are, we stacked the HD 20-40 on top of the 18-35:
The clear spacer between the two lenses is just the K-mount body cap, added to make it easier to show where one lens ends and one begins. Also, it should be noted that the Pentax Limited lens has its lens hood actually attached. Still, even with the hood attached, the lens is narrower than the filter threading, much less the entire girth of the Sigma.
What really shocked us was that if you rotate the HD 20-40, it is actually shorter than the Sigma is wide!
We aligned the Pentax so its "length" started at the lens mount, or how much of the lens would stick out of the camera. If you started at its most extreme ends from tip to tip (including the aperture lever), then the 20-40 would be about the exact width of the Sigma Art.
Mass of the Lens
Something we usually don't dedicate an entire section to, what's also important to note is the sheer mass of the lens. In fact, it shouldn't be any surprise that the lens will weigh a lot. Not only because of the constant F1.8 aperture (fast and small are paradoxes in the world of optics, after all - especially in zoom lenses), but also as a result of all the glass that's inside it - 17 elements in 12 groups. Just how much does all that add up to you ask?
To match the weight of the Sigma 18-35 with its hood attached, you would need both the DA* 16-50 and the HD 20-40 without their hoods. Using just the Limited zoom for reference, it would take almost three entire lenses to match the 811g (28.5oz) that the Sigma Art lens weighs:
At this point you may be raising an eyebrow as to why we are placing such an emphasis on these two lenses specifically. The reason is because of the endless discussions comparing the two of them and pitting them against each other. Some have come to the conclusion that Pentax should never have released their version. While we will get to sharpness and bokeh comparisons between the two so we can draw definitive conclusions regarding image quality, this physical comparison is important because the two lenses certainly do serve different purposes. The fact is the Sigma weighs a lot, especially for a lens in the Pentax mount, a lineup renowned for its compactness.
Something also to be aware of is if you plan to own the Sigma and use it for a lot of tripod work, we recommend ensuring you have a strong set of legs and tripod head. Like we said, the Sigma weighs, but it is the nature of where that weight lies that makes the camera very front-heavy. Combine this with lacking a tripod foot and the result will be some definite sagging if it isn't securely fastened to a robust tripod/head combo. This becomes even more problematic if your preference lies with large rectangular filters, which add even more weight to the very end of the lens.
Zooming and Barrel Extension
We are happy to announce that this Sigma features internal zooming. What this means is that the lens does not change its size physically when zooming the lens, ensuring nothing "telescopes" as you make your way through the focal length range. The animation below should demonstrate that clearly:
The zoom ring is excellently damped, and if anything a bit on the tight side at first feel. When mounted on our K-3 and K-5 IIs, it turned smoothly yet left us with confidence that even if you banged it around your last focal length setting wouldn't change accidentally.
One thing to note is that on occasion, lenses from third party manufacturers have a "backwards" zoom ring. What this means is that the zoom direction is opposite that of Pentax's choice to go counter-clockwise from lowest focal length to highest. Another way to think about it is when looking at the lens, the lower focal length is to the right, with higher millimeter settings to the left. We are happy to report that the 18-35 mirrors the Pentax direction when zooming (but not focusing, as you'll see next).
Internal Focus and Focus Distance Scale
Just like the internal zoom, the Sigma 18-35 also features internal focusing. Along the same lines, it means that no part of the lens's physical construction expands, contracts, or rotates when focusing the lens between infinite and its minimum focus distance. The below animation should prove that claim:
The distance scale, which indicates the distance from the subject or point in focus, is kept within the small window shown above. Because it is difficult to see from the above animation, we included this non-animated close up as well:
As you can see, the distance units satisfy both American and rest-of-the-world standards. Additionally, the attention to detail in constructing the lens is apparent here as well. No bulges, cracks, or obvious edges can be found. Aside from the texture difference between the plastic barrel and the glass (plastic?) window, they are perfectly flush with one another and reinforce the feeling of stellar quality.
Just as above with the zoom ring, the focus ring had that perfect combination of "smooth stiffness." Lastly, there are no depth of field markings to indicate the "zone of focus" by aperture.
For the actual performance of the focusing system, we'll visit all aspects of it on the following page of this review.
Rear Lens Mount and Rear Lens Cap
The rear lens mount is what you would expect from a premium grade lens: an all-metal mount with very smooth finishes.
Additionally, due to the lack of weather sealing, this lens does not have an o-ring/gasket to create a seal when mounted on the camera body.
Lens Hood
The lens hood that comes with the 18-35 is very solid, no doubt made from the same highly durable Thermally Stable Composite encasing the innards of the lens itself. Upon attaching the hood, it requires a good bit of force to snap it into place, promising to never come accidentally unattached unless you consciously choose to remove it. The below animation shows how the Sigma 18-35 "Art" looks with and without the included hood:
The ring that appears around the base of the hood is no more than a means to get better grip on the hood while rotating it into place. It does not rotate freely like the zoom or focus rings below it on the body of the lens.
Reversed Lens Hood for Storage
One of the most important things about having a lens hood is making sure you bring them with you. For traveling photographers, having a hood that doesn't take up any additional space is a boon not to be undervalued. For the 18-35, we are happy to report that not only does the lens hood properly click-in in a reversed orientation for storage, but it also does so in a very minimalistic manner so you never have an excuse to leave it behind:
With how slim the lens hood is, and how flush it fits along the body without sticking out, we couldn't help but feel that the DA* 16-50 could take a lesson from the Sigma:
Variable Aperture Range Chart
It's been mentioned that this is a constant F1.8 aperture lens, however all the lenses being compared to it, namely the Limited zoom from Pentax, aren't. The HD 20-40 is a variable aperture zoom lens with an iris of F2.8 to F4. In order to make it easier to visually grasp the exact aperture range of Pentax's all-metal zoom, namely where each maximum and minimum aperture lies along the entirety of its focal length range, we've created the following diagram for you. In addition to these two, we also added the other two lenses that will be compared against in the following pages.
Above the axis lie the maximum apertures, with the minimum possible openings underneath.
Without getting to the image quality comparisons, these two lenses—the Sigma 18-35 and the HD 20-40—are the best representation of lens design philosophy we can think of. The dichotomy is simple - either you prioritize the maximum speed/aperture (the Sigma "Art") or you focus on overall compactness of the entire lens (the Limited zoom). The resulting products of either emphasis results in a stark difference, which we examined in depth above in the size and weight comparisons.
Verdict
There really isn't much else to say. The Sigma 18-35 "Art" is a marvel of engineering in the physical sense (we'll get to the optics shortly). Excellently crafted, extremely tight tolerances, and perfect levels of dampening in the two rings. It's extremely robust, and really is the caliber of lens one would expect to match with the equally tough-as-a-tank Pentax bodies.
But, with that robustness comes one caveat - it was realized right away just how heavy this lens was. For those who love the Pentax's DA and FA Limiteds whilst eschewing massive imaging systems, this lens will not be for you. Within a few minutes the combined mass of the K-3 and the 18-35 became immediately apparent. And ladies, our reviewer doesn't shy away from the gym.
Of course, we have to take a step back and put things into perspective, being sure to remember that we are holding a zoom lens with a constant aperture of F1.8, a feat hitherto thought impossible.
Lastly, it goes without mention that as Pentaxians who have come to expect rather than hope for dust and moisture resistance in our lenses, we regret to say that Sigma opted not to seal it. Which is a shame, because that easily would have made the Sigma 18-35 "Art," in combination with Pentax's in-body image stabilization, the gold standard for photojournalism and event photography, regardless of the conditions. The lack of weather sealing is all the more surprising considering the astonishingly tight build tolerances as well both internal zooming and focusing.
