Sigma's 17-35mm f2.8-4 EX is one of the EX Series lenses. It combines a fast f2.8-4 maximum aperture with ultra wide angle zoom lens of 17-35mm. It incorporates aspherical lens elements in the front, as well as rear lens groups, to correct spherical aberration. It also incorporates internal focusing to prevent deterioration of the optical quality at close distances and to eliminate rotation of the front barrel during focusing. A "perfect hood" is provided. The lens materials used in this new lens are lead and arsenic free ecological glass.
Aspherical lenses
Lens elements that are not spherical can reduce the total number of elements required in a lens design. They can deliver better performance while reducing weight and size. Aspherical lenses maximize optical performance while minimizing lens size and weight. Aspherical lenses help reduce some of the problems usually associated with wide angles and zooms, such as lens flare and edge distortion. They also help deliver higher quality telephoto images.
Specifications:
- Lens Constructions: 14 groups, 15 elements
- Angle of View (Diagonal): 103.7º-63.4º
- Number of blade in diaphragm: 8
- Minimum Aperture: f32-45
- Minimum Focusing Distance: 19.7 inches
- Magnifications: 11.5x
- Filter Size: 82 millimeters
- Dimensions (Dia x Length): 3.5 by 3.3 inches
- Weight: 14.1 ounces
Product Description:
The lens covers a super-wide angle of view 104°and has a large-aperture. It has a minimum focusing distance of 27mm at all focal lengths, and maximum magnification ratio of 1:4.5. The models which are equipped with HSM (Hyper Sonic Motor) system are ensured a quiet, high-speed AF as well as offering Full Time Manual Focusing. Special Low Dispersion (SLD) and two aspherical glass elements provide excellent compensation for distortion as well as for various aberrations. The design concept of this lens is especially suitable for the characteristics of Digital SLR Cameras. The high performance inner focus system is particularly suitable for using circular polarizing filters and a petal-type hood as the front of the lens does not rotat