While the Tokina 10-17 gets a lot of (well deserved) accolades from u/w photographers, there are some cases where a rectilinear lens is called for. For cropped frame cameras like the Canon 7D or the Nikon D300s, the typical rectilinear wide angle zoom lenses people use underwater are the Canon 10-22, Nikon 12-24, Nikon 10-24 or 12-24, Tokina 11-16 or Sigma 10-20. Then there is the new Sigma 8-16mm F4.5-5.6 DC HSM ultra wide zoom lens. This is a wide lens, with a diagonal FOV (field of view) at 8mm of about 121º. For comparison, the Canon 10-22 FOV is 107º at 10mm. (Note, though, that the Tokina 10-17 diagonal FOV at 10mm is nearly a 180º fisheye view).
I had a chance to take the Sigma 8-16mm for a couple of dives recently. I outfitted it to my Canon 7D, in a Nauticam NA-7D housing, and brought along 3 different sizes of extension rings. The dome I chose was the Zen Underwater 230mm superdome. Corner sharpness is certainly something to be considered with this wide lens, and the big 230mm dome was my choice to get the sharpest possible corners. After trying the various Nauticam Locking Extension rings, I settled on the 60mm ring; no vignetting seen with this extension at any zoom setting, and corner sharpness turned out to be good.
The super dome makes over/under shots much easier than with a smaller dome. The 8-16mm was a good lens choice for this shot taken at the Dry Tortugas; note how it keeps the lines of the old coaling dock straight. This is one shot where a rectiliner lens like 8-16mm lens is needed, and the Zen 230mm dome makes it an appropriate combination for over/under shooting.
Corner sharpness is of course dependent on many things including distance to the object in the corner, but at f/7.1 or smaller aperture I was usually ok with the corners. I did notice some transverse chromatic aberration around the edges at all apertures. You can also see from this shot the relative lack of distortion, and that the straight lines look like straight lines.
More here: Getting wide the Sigma 8-16 Nauticam USA
I had a chance to take the Sigma 8-16mm for a couple of dives recently. I outfitted it to my Canon 7D, in a Nauticam NA-7D housing, and brought along 3 different sizes of extension rings. The dome I chose was the Zen Underwater 230mm superdome. Corner sharpness is certainly something to be considered with this wide lens, and the big 230mm dome was my choice to get the sharpest possible corners. After trying the various Nauticam Locking Extension rings, I settled on the 60mm ring; no vignetting seen with this extension at any zoom setting, and corner sharpness turned out to be good.
The super dome makes over/under shots much easier than with a smaller dome. The 8-16mm was a good lens choice for this shot taken at the Dry Tortugas; note how it keeps the lines of the old coaling dock straight. This is one shot where a rectiliner lens like 8-16mm lens is needed, and the Zen 230mm dome makes it an appropriate combination for over/under shooting.
Corner sharpness is of course dependent on many things including distance to the object in the corner, but at f/7.1 or smaller aperture I was usually ok with the corners. I did notice some transverse chromatic aberration around the edges at all apertures. You can also see from this shot the relative lack of distortion, and that the straight lines look like straight lines.
More here: Getting wide the Sigma 8-16 Nauticam USA
