Sigma 15mm f/2.8 EX DG
Introduction
This is a fantastic super-wide fish-eye lens with a decent close focus capability allowing you to get in tight with your subject and still capture their environment.
The ability to get a nearly 180º Angle of View is rare and even rarer when it is this affordable and works this well. Combined with something like a DxO software product that can bring you back to a reticilinar photo, you have a great setup.
Specifications
The lens is setup with 7 elements in 6 groups.
Maximum Aperture: f/2.8
Minimum Aperture: f/22
The diaphragm is 7-bladed, producing an okay bokeh.
Auto-focus via screw (no motor on the lens) as well as integrated electronics to talk to the camera and set EXIF data.
Construction
Constrcuted with plastic parts all over. There is a latch for the aperture ring to keep that choked-down.
The petal-shaped lens hood is integrated into the design with a unique lens cap that slips over the whole setup, protecting the front element and the lens hood. If you are using this lens ona Dx camera with its crop sensor you can shoot right through the lens cap.
Performance
The lens works works very well. With its auto-focus it speeds up handling to compose shots.
The large aperture permits photos with a pleasing depth-of-field to highlight a subject in the frame but with such a wide angle of view so many things are going to be in the photo so it is best to choose wisely how you compose your shot.
Examples
Following are some sample photos to demonstrate the power of this type of lens and some general uses which will likely yield good results. If you shoot things like these, then this lens may be a good one to think about adding to your camera bag.
Check out more photos I have shot with this lens in my Flickr Album.