Sigma announced two fisheye lenses Wednesday, one with a 4.5mm focal length and the other a 10mm model--for Canon, Nikon, and Sigma SLR camera owners who want to photograph extreme wide angle views.
Fisheye lenses capture light from an extremely broad angle, but produce distorted views of the world with parallel lines bowing outward. That distortion can be annoying, but many enjoy it as an artistic effect--think giant bulging faces in the foreground dominating tiny trees beyond--and scientists use some varieties of fisheye for precise measurements such as the sky's cloud cover.
But the digital SLR era has thrown a wrench into how the fisheye lens works. That's because the vast majority of digital SLRs sold today--including models such as the Canon Rebel XTi and Nikon D40x---use image sensors that are smaller than a full frame of 35mm film. Because these smaller sensors don't record light that would fall on the outer edges of a full frame of film, the cameras record a narrower field of view. Fisheye and wide-angle lenses, therefore, need to be designed with even shorter focal lengths to compensate.
Sigma announced two fisheye models, both with an f/2.8 aperture. The 4.5mm F2.8 EX DC Circular Fisheye produces a circular image that spans a full 180-degree view in all directions. The 10mm F2.8 EX DC Fisheye HSM, in contrast, fills the whole sensor frame, with a 180-degree field of view stretching from one corner of the frame diagonally to the other when used on Nikon cameras. In other words, the 4.5mm lens captures more of the periphery.
Because there aren't standard image sensor sizes for the smaller sensors, lenses behave differently on Canon, Nikon, and Sigma SLRs. The 10mm model shows a narrower 167-degree field of view on Canon SLRs and 154 degrees on Sigma SLRs, Sigma said.
Judging by the respective Japanese Web sites, the 10mm model will cost 90,500 yen, or about $820, and be available in December, and the 4.5mm model will cost about $1,040.
Update: Sigma responded with further pricing information for U.S. markets. The 4.5mm lens will have a suggested retail price of $1,400 and an expected street price of $900; the 10mm lens will have a suggested retail price of $1,000 and an expected street price of $650.
Both lenses can focus as close as 13.5cm, or 5.3 inches, from the focal plane. On the 10mm model, that's just 1.8cm, or 0.7 inches, from the front of the lens. Both use quiet hypersonic motors and special low-dispersion glass to minimize chromatic aberrations.