EDIT: I added my findings after testing both lenses Edit2: After 2 days of testing I am very happy about the Sigma 10-20. I think the results are just amazing. Hi, I just did a small comparison of the Sigma 12-24, Sigma 10-20 and Tokina 12-24 for myself but thought this would be interesting for some people here: Most of my findings based on the reviews and charts of www.photozone.de and partly my own testing Sigma 12-24 Pro Nearly no distortion A little vignetting at the wide end but very little from 14mm on Excellent build quality Good to very good resolution HSM Sigma 12-24 Contra Shows some CA Not an F4 Front element allows no filters lowest resolution from the 3 at 12mm Sigma 10-20 Pro (Tested by myself) Excellent resoultion throughout its range and especially at the wide end. Nearly no CA. The results in this regard are just awesome and incredible. Why could not Nikon do this with the 12-24? Little distortion excellent build quality 10mm HSM Excellent sharpness Sigma 10-20 Contra (Tested by myself) Vignetting, lens needs to be stop down (Most tests mention vignetting but I did not see it as such a big problem so far. Little vignetting IMO only) Not an F4 Less Contrast than Tokina (Can be an advantage for contrasty scenes. It gives you more dynamic range) Less saturated than Tokina 12-24 but still good Tokina 12-24 Pro (Tested by myself) Superior build quality F4 Good to very good resolution Very little vignetting compared to the others Excellent contrast Excellent sharpness Excellent saturation Tokina 12-24 Contra (Tested by myself) A lot of CA all over the picture In contrasty scenes, night shots for example, CA can not be removed Highest distortion of the 3 but still good No built in motor (But I think this is not a very important factor) So what is the vedict: I would say that the Sigma 10-20 is doing excellent. The high resolution is a big advantage, especially if you are planing to use it at the wide end. The Tokina has the best image quality in total if you disregard CA and distortion. The Tokina is also sharper at the corners. CA is horrible at night shots with the D2x. The Sigma has nearly no CA in comparison, especially in contrasty scenes the Sigma is much better. The final answer is: If you are shooting high contrast scenes then buy the Sigma 10-20 because: Less CA Lower contrast of lens helps to maintain a good dynamic range If you are shooting low contrast scenes then buy the Tokina 12-24: CA is not a problem with low contrast scenes Color and contrast improves the total image quality. Somebody I know uses the Tokina mainly in the golden hour. This is were the Tokina shines and is really awesome. But if you are doing a lot of night shots and any shots from 10am to 3pm (normally high contrast scenes) then the Sigma is the better choice. I think it is still difficult to say who is a winner because not one of them has no cons. The Tokina was my favourite for a long time. I heard a lot of good things about it and saw incredibles pictures with it. I think this makes the whole part the most difficult. The F4 advantage of the Tokina is really not that critical because most landscape shooters shoot anyway at F8 or higher. There are a lot of sample pics out there but not one which compares these 3 lenses. Hopefully somebody who has access to all these lenses will do a test in the near future and give us some information. Of course would it be great to include the Nikon 12-24 in this too. From what I have read is that the Nikon 12-24 is the best regarding color, saturation, contrast and sharpness. I am pretty sure that the Sigma 12-24 handles distortion better. Other than that the Nikon is the winner in most tests. Therefore it costs of course more. But the build quality is not excellent and it shows distortion and CA. Therefore I think that the price is pretty high in comparison to the marginal optical advantages you get.