Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- User Rating: 
Summary for Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- Impressive performance and value.
Notes on Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- I bought this lens to service a new client that does virtual tours for hotels and resorts. Their lens requirements are 18mm for full frame digital cameras and 12mm for DX chip cameras, to shoot 360 degree VRs. I didn't want to invest the 1000.00 plus dollars for another Canon lens and Canon or anyone else for that matter doesn't make a lens with this range. The Sigma would allow me to use both my 1Ds Mk II and 20D to service this client and cost me half what anything Canon provides.
Having bought the lens mainly for Internet content, I wasn't going to be too critical about image quality from it, but I've been very surpised and pleased by it's performance. This lens has the least amount of barrel distortion of any wide angle zoom lens I've ever used. Even less than some primary lenses. To the point where it is essentally undetectable to the naked eye. It has less barrel distortion than my 1000.00+ 24-70mm f2.8L Canon lens! Operation is smooth, fast and constructions is first rate. I haven't done any critical sharpness comparisons yet, but I haven't noticed any problems from the images I've taken so far.
The lens has a very bulbous front element, so conventional filters and lens caps won't fit. But Sigma cleverly includes a high quality adapter ring with filter threads in one end that slides over the built in lens shade on the lens. A lens cap is also included that fits on the end of the ring to protect the front element while being stored. The ring vignettes at 12mm on a full frame camera, but does not on DX chip cameras. So on those cameras, conventional thread on filters can be used with by screwing them on to the end of the adapter ring. You could do also this on full frame cameras, at longer focal lengths. A gelatin filter holder is provided on the back of the lens, but I can only imagine this being useful with film cameras.
Overall, I'm very impressed and satisfied with this lens. I highly recommend it.
Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- User Rating: Summary for Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- Good Super Wide for Price
Notes on Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- I bought this lens because the Nikkor version was simply overpriced. I usually do not like Sigma products but I needed a super-wide angle lens and my choices were limited for my budget.
I thought I would be settling for something less, but WOW! Actually the lens produces good images for interior architecture work. There is some color fringing but you have to magnify extremely close to see it. The aberration is what you would expect from a lens of this type. All of the above are easily corrected in Photoshop.
Pro's : Sharp images, good color and quiet Auto-focus. Minimal aberrations for the money.
Con's: Front element is a "popeye" which is not favorable for filters
Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- User Rating: 
Summary for Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- Good wide angle, very bad optics
Notes on Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- I ordered this lens because I wanted the widest angle without getting a cropped lens (the Canon 10-22). I have had great luck with Tamron 3rd party lenses and the price was great so I thought what could be better? I should have paid more attention to what everyone else said about quality control. On the good side the wide angle is truely fantastic (can't wait to see the 10-22). Also the color responce, saturation, and contrast are absolutely stunning. Comes out right with no post production needed. Unfortunatly the good ends there. As far as sharpness, clarity, and focusing the camera is simply not usable. It is simply the worst quality lens I have eveer used. Even manually focused, stopped down, high shutter speeds, and clear skys this lens is so blurry and fuzzy you think you took it with a cheap camera phone. Not to even start about the chromatic ab., noise, and fringing. None of my images were usable at all. I decided that wasn't worth the price and I didn't want to deal with sending it back to Sigma 2-3 times like others had when I could get a Canon 10-22 for a bit more and know I will get good quality. Don't get this lense, it isn't worth the money. (If you are using a full frame camera like the 5D then it would be a shame to put such a bad lens on it. Get the Canon 10-22. Not to mention the Sigma really is huge with rather poor quality construction. The zoom and focusing ring were also almost impossible to use.
Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- User Rating: Summary for Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- Unique Ultra-Wide Angle Lens But Poor Sigma Quality Control
Notes on Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- There's nothing else this wide for use on a full-frame 35mm camera or digital such as the Canon 5D. It's so wide on a full-frame that you can almost see behind you (well not quite, but close to 180 degree field of view). It is not a fisheye, so straight lines stay straight. There is some minor vignetting at 12mm but less than the Canon 17-40 L-lens I had at 17mm. This lens is pushing the limits of physics so it is not as sharp as some lenses but it takes in so much more of the view and provides a crisp image all the way to the corners.
For use on a cropped sensor camera, such as the XT, 20D or 30D a better choice may be the Canon 10-22mm which is uber-sharp in the middle of the frame. The Canon, however, gives fuzzy images on the sides when wide open but sharpens up when stopped down to f8 or more. My third copy of the Sigma lens is less sharp than the Canon in the center of the frame but is sharper starting about halfway to the edge when both lenses are wide open. Near the edges of the frame the Canon gives a dark and mushy image when wide open at 12mm while the Sigma is only slightly less sharp than at the center - truly amazing!
Unfortunately, Sigma lenses are seemingly sold "as-is" with wide sample variations. The autofocus died on my first copy of the lens after less than 30 pictures. The second copy had poor optics with soft and fuzzy pictures even when manually focused. The third copy is sharp at 12mm, even wide open, all the way to the edges, but only if manually focused. At 12mm the lens autofocuses too far away when an object is close and too close for distant objects. At 24mm it autofocuses right on but is softer than at 12mm. I've decided to keep it since it is easy to manually focus. The depth of focus is large at 12mm. For objects further than a few meters away when using 12mm just set the lens to infinity and everything from a few feet to infinity is in focus even at the edges of the frame and in the corners. The lens has a 4-year warranty so I may send it in to Sigma for calibration later.
Pros: (1) Unique ultra-wide angle perspective on a full-frame camera. (2) A good copy will be optically sharp all the way across a full frame, even wide open. Further, there's virtually no purple chromatic aberation near the edges of dark objects with bright backgrounds. (3) Nice build quality with good finish and large smooth focus ring. (4) Straight lines stay straight so no defishing needed (defishing uses interpolation which lowers resolution away from the center). (5) Lens comes with a case and has a small built-in hood (serves mainly to protect the front element). (6) 4-year USA warranty if purchased from an authorized dealer like Amazon or B&H. Otherwise you get a 1-year International Warranty.
Cons: (1) Wide sample variation - getting a good copy takes luck or persistence while trying multiple copies. (2) The bulbous front element (this lens is nicknamed "Popeye") is exposed and no standard filter can be used for protection so be very careful. (3) Flares easily. The sun does not need to be in the picture just anywhere not behind you. This is a result of the ultra-wide design and not a fault of Sigma. (4) Photos sometimes come out too bright, giving the appearance of low contrast. Photoshop or other software easily fixes.
Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- User Rating: Summary for Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- Professional 12-24 lens
Notes on Sigma 12-24mm f/4.5-5.6 EX DG IF HSM ...- I use this lens primarily for architectural work. It's rugged, fast focusing, and most important, distortion free (i.e., straight lines stay straight). Dramatic design, built for full frame use if (when) you decide it's time to go that way. It's also performed extremely well for landscapes....even some shots at weddings. My most frequently used lens. (Hint: on the APS-C format digital SLRS, you can leave the accessory ring on the lens - it provides additional flare resistance, and there is no vignetting.)
