The Sigma 12-24mm f/4.5-5.6 EX DG Aspherical HSM is an incredibly ultra-wide angle lens available for a variety of cameras. It is part of Sigma's EX series which boasts top optical quality and a rugged build. Image quality is nice, and you are not going to find a rectilinear lens with a wider field of view than this beast.
The Sigma 12-24 is a rectilinear lens, meaning that straight lines stay straight. Think of the bulging, curved lines characteristic of photos taken with fisheye lenses -- the 12-24 is wider than some fisheyes but it keeps those lines realistically straight. This makes it well suited for photographing things with… what do you think? … straight lines. Think architecture.
Corners sometimes look dark when shooting near this lens' max apertures of f/4.5-5.6. You can fix that with the vignette controls in your post processing software. And while we're talking about the corners, that is where some of the more severe distortion takes place with this lens. Be mindful of subject placement, e.x. putting a person's feet near the corners of the frame can make it appear as though they are walking around on skis.
I consider the 12-24 to have very good image quality and sharpness for a lens of its kind. Colors and contrast are all satisfying, and sharpness is good. It can be a little soft wide open, but when you close the aperture down to around f/8 or smaller sharpness gets much better. There are a lot of lenses sharper than this one, but most of them are completely different types of lenses and so comparisons really don't make sense -- it takes a lot to make a lens this wide.
The 12-24 features HSM, Sigma's high performance auto-focusing motor. Focusing is fast and accurate and I have no complaints. Then again, this is not a lens with which I shoot moving subjects. Virtually everything I've ever photographed with this lens was stationary.
Flare can be an issue with this lens -- it gets picked up very easily, and you'll need to move your composition around in order to get rid of stray light. Notice the flare in the bottom left corner of the following image.
Ultra Wide Angle
The Sigma 12-24mm is as wide as it gets. This is the widest rectilinear lens available for full frame cameras. There are others such as the Canon EF-S 10-22mm f/3.5-5.6, but that lens is only compatible with APS-C crop cameras.
When you look into the viewfinder through the Sigma 12-24, you may find it hard to believe how much area is actually captured in the frame. At times, you may struggle to keep your feet or the legs of your tripod out of your photos! Be mindful of the angle of your light source, or you'll start seeing your shadow at the bottom of many photos.
The Sigma 12-24 is built rugged. The mount is metal and the barrel is heavy. The front element bulges out like a bubble and so you are not able to attach traditional filters. It also features a built-in petal-shaped hood that helps to protect that large, bulbous front element.
The 12-24's lens cap gets on my nerves a lot. It is made up of two parts -- a holder that slides around the built-in hood, and then a lens cap that attaches to the holder. When full assembled the lens cap easily slides on and off. I wouldn't hang a camera with this lens attached over my shoulder with the cap on, as it would probably slide off and get left behind.
The Sigma 12-24mm f/4.5-5.6 EX DG Aspherical HSM is the widest lens you can get, especially on a full frame camera. This of course is the main draw of the 12-24. It's not made for low light photography and it doesn't have world-class image quality, but it takes ridiculously, unbelievable wide photos. And it does that job very well. It doesn't have a permanent place in my bag and I don't use it often, but it comes along when I have specific ultra-wide photos in mind.
Where to buy the Sigma 12-24mm f/4.5-5.6 EX DG Aspherical HSM
Sigma makes this lens for a variety of lens mounts, so choose the version that matches your camera:
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