Excellent underrated lens, if you buy the right model
I recently bought this lens for Nikon D7200, after doing lot of research online and watching many videos. Many of the reviews have mixed opinions, but luckily I bought the latest model lens (please see the link for the differences - Sigma 24mm 1.8 EX DG different versions ) . I have made a thread where you can see the different versions of lens and my review is on the new model lens I bought.
The lens came with wrong AF and I had to do the AF tuning in my camera for this lens, which took me around 10minutes. I had to adjust around +17.0 to make this lens autofocus properly on my camera. This model lens is still available in Sigma website, but apparently they stopped making this lens for Nikon/Canon/Sony/Pentax after introducing the ART lens. The lens is still available for Sigma mount in the official website. This lens is not only the lens for landscape, but also for low light shooting of the events, and very good macro photography where you can cover more space in the frame if you wish. It can be a very good all time use prime on an aps-c camera.
Myths and truths:
1. Few reviewers claimed the lens has the AF issue, where the AF creates lots of noise. But the truth is, the AF is as smooth as in Sigma 17-70mm DC HSM and it focuses very quickly, even in bad lighting conditions.
2. One of the Canon review mentioned the manual focus is tough as the focus ring does not rotate fully. But the truth is, the manual focus is super smooth and very convenient, because you need not keep on turning the focus ring until it focuses. Such mechanism really annoys at this focal length, where I would't spend a lot of time on focussing.
3. One of the video review claimed the focus at 1.8F is not very smooth. From my experiments what I understand is, the reviewer did not tuned the AF before posting the video or he must need glasses if the review was done in manual focus. I have taken more than 20 images in different lighting conditions and the photos are very crisp at the point where it is focussed and it creates very good shallow depth of field where it is not focussed. Even the edge sharpness is far better than most of the other similar lens out there.
4. Some reviewer mentioned the lens is not a very good choice for aps-c sensors. But the truth as many knows, DX sensor uses the sweet portion of the lens to create crisp images. On my D7200, I have never seen any lens at this price range performing better than this lens at this focal length. It can easily compete with similar $$$$ 1.8 FF lenses.
5. The lens has the great ability to minimize the distortion and CA, due to the Aspherical material in the lens. I generally don't see any distortion while capturing most photos and if there are any, lightroom identifies the lens and I can remove in 1 click. Chromatic Aberration is something I have not seen much with this lens.
6. Because very few reviewers did some reviews and gave bad rating (I strongly believe the bad rating is for the older version of the same lens, which I never used. Which is said to have the different focus system, where the front part of the lens does not rotate while auto focusing) this model of the lens is underrated and you can pick these lenses very cheap in ebay. Be sure to get the right model and test.
7. The only drawback of the lens is its weight. The lens weighs around 485grams (while Nikon AIS lens weighs around 260 grams), which is because of the 9 out of 10 elements in the lens. It is a greatly made lens by Sigma and with the quality of the images what I get, I don't mind carrying another 200grams with pride. More than everything, it is an all purpose lens on my D7200 camera, because a)Great macro b) nice portrait images with shallow depth of field c) very good lens for wedding shoot or an event shoot and d) wide aperture is awesome for night photography e) a true wide angle lens for architecture and landscape shooting without any noticeable distortion.
I highly recommend this lens if you are shooting with an aps-c camera, but it could be even better on Full Frame cameras.