Good Morning,
I have both lenses and they are very complementary to each other. If you look at the diagonal field of view, each one has this field of view:
- 10-17 -180 degrees to 100 degrees
- 12-24 - 100 degrees to 60 degrees
Depending on the scene, the objects in the scene, your composure, along with the selected focal length, you can pretty much mitigate the fish eye effect for any of the focal lengths selected. If the objects in the frame are very square with linear lines, then the effect will be very pronounced - your eye will detect at to what they should look like and the fish eye effect can be very pronounced. On the other hand if they are "natural" with curves, etc. - think rock formations etc., then the eye really does not detect the fisheye effect at all. This lack of perception extends especially to the long end - 17mm where the fisheye effect is pretty well under control. Composition is important with the 10-17 where with a slight adjustment, in either up, down or straight on, you are able to place the "bend" at the top center or bottom. At 10mm you can have a very straight and level horizon, and if the foreground is dirt or something not straight or rectangular then you will never see the bend.
The other comparison that comes to mind is that the 10-17 when compared to the 12-24 can have a lot more contrast and the colors are a bit more vivid. The "sharpness" of the lens will appear to be different - since the field of view is so large in the 10-17, each pixel needs to capture a lot more area, as compared to the 12-24. This is not to imply that the 10-17 is soft and not sharp by any means.
Other 10-17 characteristics that you will see with use are - when compared to the 12-24, the center is pushed back into the background in order to pull more scene in from the top, bottom and the sides. This said, you can get incredibly close to very LARGE objects and still get EVERYTHING into the frame. When used in portrait orientation, check to ensure your feet or shoes are not in the frame at the bottom.
You should like the lens - its construction and build quality are outstanding. Its size compared to the 12-24 is pretty small.