Sigma 15mm f/2.8 EX DG Diagonal Fisheye Lens Review, With Many Pictures – Simply a fantastic user review and some nice Canon EOS 5D Mark II images by maiaibing, who concludes:
It's a great lens that has lots to offer for anyone who like wide angle shots. Colors and flare resistance is tops. Center sharpness is very good even at wide open aperture, while corners tend to be soft and suffer CA (chromatic aberration) unless it is stopped down.
Some other interesting bits of information that I learned in the post follow.
Optical characteristics:
The Sigma 15mm is diagonal fisheye, and fills a FF (full-frame) picture across the entire sensor.
Why buy a fisheye lens?
Three main reasons; its wider than a standard lens (so 15mm fisheye is much wider than a 14mm standard lens) by not correcting the light (as much as a traditional lens), the fisheye should have less flare and better – even spectacular – colors.
Metering and exposure:
Colors are also great, but fisheye lenses can be very tricky for the camera's light meter. So with the 5DII I often shoot @ EV -2/3 to -1½ to compensate for overexposure in bright daylight.
AF (autofocus performance):
Some people have complained that the Sigma may hunt at low light, but I do not find it more difficult to use than most other lenses – actually I find it quite good. It has worked fine from early morning, over heavy rain to dark night.
Tips on shooting with a fisheye:
The important aspect of shooting a fisheye is to use the focal plane very actively in your shots. There is a dramatic shift in the look and feel of a shot depending on the tilt to the horizon and where in the picture plane your objects are. Also, as long as you shoot "rounded" objects such as people, a fisheye often works better than a traditional wide lens like the Canon 14L. On the other hand its not very good at buildings unless you use software to correct. The ability to use software to straighten out the curved lines makes fisheye lenses more versatile than ever.
maiaibing added:
The Sigma is an "EX" lens, which means "Excellent". One of the trademarks of Sigma "EX" is a high build quality. This is my third "EX"-lens, and they have all stood the test of time and use. There are some mixed reactions to Sigma's black powder coating but I like it and it seems durable.
The lens is not HSM and is therefore not silent. Instead you get a low whirring sound when focussing. However, more often than not, people will not notice as it drowns in the backdrop of the ambient sound.
