Sigma - 12-24mm f/4.5-5.6 EX DG HSM Review

About the Sigma 12-24mm f/4.5-5.6 EX Aspherical DG HSM Autofocus Lens
Whew! That's a mouthful. I'm new to camera lens reviews so first let's go through what all of those numbers and letters that look like half an Algebra equation mean. If you're a seasoned camera pro, feel free to skip this section and head straight to the technical specs below.

First, about the brand: Sigma Corporation of America is one of many well-known lens manufacturers for SLR cameras. They also make the Sigma SD10, a Foveon-based chipset digital camera - technology that makes me drool, but isn't mainstream enough for me to adopt just yet. So, Sigma knows cameras, and they know optics. I trust the Sigma brand to deliver a solid performing lens.

12-24mm f/4.5-5.6: The lens is classified as an "ultra wide-angle" lens at 12-24mm. With the 1.6 multiplier the lens is approximately around 19-38mm in standard camera lens terms. The maximum aperture that this lens is capable of is f/4.5 to f/5.6 at 12 to 24mm respectively.

EX: An "EX" lens is a Sigma notation for an exterior finish and quality level. In their words EX denotes, "the superior build and optical quality ... to enhance its appearance." So to me, EX means, "It's pretty and you're paying for it." I don't know if this is entirely the meaning Sigma wants associated with the notation, however.

Aspherical: I'm really not sure what to make of how Sigma uses the notation 'Aspherical' in their description. They write the following: "The aspherical lens complex allows freedom of design, improved performance, a reduced number of component lenses and a compact size." So presumably this means the design of the lens is optimized to reduce its size. Big time pros with lots of lens experience, leave a comment to correct me if I'm wrong.

DG HSM: DG simply means the lens is optimized to compensate for the "shortcomings" of these new digital SLR's with their crop or multiplication factors. The lenses are wider angled, with shorter focus distance. HSM stands for "Hyper-Sonic Motor". Given Sigma's claims about their HSM technology, you should expect that an HSM lens will provide a quiet, fast autofocus.

So that's the Greek lesson for today. On to...

Relevant Technical Specs: (Provided from Sigma's website)
- Lens Construction: 16 Elements in 12 Groups
- Angle of View: 122 - 84.1 degrees
- Number of Diaphragm Blades: 6
- Minimum Aperture: f/22
- Minimum Focusing Distance: 28cm / 11 in.
- Maximum Magnification: 1:7.1
- Filter Size: Rear Type (Gelatin Filter)
- Dimensions: Diameter 87mm X Length 102.5mm
- Weight: 600g / 21.6 oz.

Using the Sigma 12-24mm Lens
Okay I hear you, enough about what Sigma says about their lens, so here's what I have to say about it... This lens is actually easy to use and completely intuitive if you're used to standard zoom camera lenses. Mount them onto your camera and they're just like everything else.

One thing I noticed about this lens immediately upon opening it is that it's huge and it's wildly conspicuous. I know one owner who referred to his Sigma 12-24mm affectionately as "Popeye" because of the enormous, fisheye-looking glass element.

I was uncomfortable using this lens due to its form factor for several reasons: First, it just screams high end camera lens, even to casual passersby, which is an invitation for theft in some areas. Second, the protruding lens element and the fixed-petal hood made it impossible for me to buy a filter to affix over the lens glass itself. I like to buy (relatively) inexpensive UV filters to affix to my nice camera lenses in order to protect the more expensive glass of the lens. That's impossible to do with this lens because the fixed-petal hood doesn't allow for any sort of threaded lens filter to be attached.

Not only can you not simply protect the lens with a filter, but the hood and bubble glass make it impossible (or nearly-so) to use polarizing filters and graduated neutral density filters, both of which are highly effective accessories for taking dramatic landscape images.

Note on filters for this lens: I should point out however that reason 1,567,598 why I love the Internet is that if you search Google you will find that there are people who have actually melded plastic rings to fix around the lens petal hood, in order to rig up neutral density filters, and in some cases even polarizers with limited success. One such chap from the UK offered to sell me a home-grown version of his neutral density filter holder for the cost of making it, after I expressed interest on a camera bulletin board. I paid him via PayPal and a few weeks later a home grown filter holder for my Sigma arrived in the mail, just one good-hearted soul across the pond reaching out to another photography enthusiast. So this huge drawback can be managed around by the enterprising, experimental geniuses out there who are willing to develop the time and the workaround on their own. To date, I don't know of any commercial filter holders available for purchase for this lens.

Image Quality
Technically the Sigma 12-24mm lens produces fantastic results for its price range. There are some minor optical flaws, which might be major for some users of the lens.

Chromatic aberration, or color fringing around picture elements is about the same with this lens as it is with any other non-professional level zoom lenses I've used. It's not terribly noticeable and unless you enlarge images and look for CA, you're not likely to notice it.

Image sharpness is also good with this lens, but not great. If the lens is wide-open there is noticeable softness toward the edges of the frame, but the center is still quite sharp. Around f/11 to f/16, image sharpness is quite acceptable. In all of my use of this lens, I was rarely tempted to open the aperture up extremely wide, so image sharpness was always fine for my needs. But the one issue I've had with this lens, particularly when I was taking shots wide-open at 12mm or whenever I was using my handcrafted "filter" mount was with Vignetting, the tendency of an image to be darkened at the edges and brighter in the middle. This is a necessarily evil of the ultra-wide angle in my opinion though, and isn't quite a reason to avoid buying this lens.

The one serious issue I had with this lens was with flare, the effect where sunlight reflects off the elements inside the lens glass to cause undesirable circles of flare light. I had a real problem with flare when using this lens. Sigma doesn't necessarily come outright and say that their fixed petal hood is to reduce flare, and it's a good thing because it does not. Not at all. The petal hood, in my opinion, is more to protect the bulging glass lens than to reduce flare. I can't count the number of times I had to shoot one-handed, using the other hand out of the frame to try to block some sunlight that was reflecting and causing flare in the frame. I hated using this lens in bright light. My best shots were always at or near dusk or dawn.

Image Composition - How "Usable" This Lens Is for Everyday Photography
One aspect of this lens review that you won't find in any future "standard" lens reviews from me is how usable an average photographer (amateur to advanced amateur) will find such an ultra-wide angle lens as a part of their lens lineup. This is an important factor to consider: Is it really worth the price to have such a dedicated wide-angle lens?

If I was uncomfortable using the lens because of its heft and size, I was often frustrated by the images that I got from the lens as well, due to the fact that this lens is designed only as an ultra-wide angle lens. Most people love well done wide-angle shots, but don't quite understand how to achieve them. To shoot wide-angle you must understand placement of elements in your frame, so after a few hundred shots I began to learn what would work as a wide-angle shot and what would not. This is not the kind of lens that you keep on your camera at all times, unless you're a truly gifted professional and you know exactly what kind of shot you're looking for and are in the setting where you'll find it. My best shots from this camera composition-wise were the ones where I was taken aback by the vastness of something and had a perfect "anchor" for the image with which to capture that vastness.

Cat's Bottom Line
I enjoyed using this lens greatly when I owned it, but recently I decided to sell my 12-24mm lens and move on. When I purchased my Sigma 12-24mm 18 months ago, options for wide-angle digital SLR lenses were limited and at the time, the Sigma was an unbelievable wide-angle option at a good price. These days there are more options available and fortunately, more dollars in my wallet, so I've recently purchased a Canon EF-S 10-22mm f/3.5-4.5 lens for my new Canon 20D. (This lens will only work with the 300D and 20D, both compatible with Canon's new line of digital-only EF-S lenses.)

After using both lenses, my take on the choice is this: If you have up to $800 to spend, go with the Canon. If, like me several years ago, you must spend under $650 or it just hurts to much to spend $800, go to eBay and purchased a used Sigma 12-24mm at a discount there. It's a solid lens, but I think that the pace of technology is making it more and more of an "average" lens each day.