The Sigma 17-70mm F2.8-4 was designed to be the ideal all-purpose lens for APS-C sized sensors. With a great focal length and macro capability, the 17-70mm F2.8-4 is also equipped with a Hyper Sonic Motor (HSM) and an Optical Stabilizer (OS) for superior image quality. The HSM ensures quiet, accurate, and fast autofocusing while the OS compensates for camera shake when shooting by hand.
This lens' minimum focusing distance is 22cm and the maximum magnification ratio is 1:2.8. At 70mm, the working distance becomes 5.52cm. When it comes to telephoto, it can shoot pictures with a similar sensation to a macro lens. Also, without the need to change the lens, it enables photographers to take a close up pictures of subjects such as jewelry and flowers. In order to secure a clear field of view, the design of this lens is very thorough, even down to the precise position of the engraved letters on the lens.
For a which is used lens used in everyday situations, the small size makes a big difference. By incorporating a smaller OS unit and optimizing the structure and power distribution of optical elements, the lens barrel has now become more compact. In order to ensure high accuracy of the product, the new compound material TSC (Thermally Stable Composite), which has high affinity to metal parts, is introduced for the lens barrel. It results in better durability of the parts and smaller zoom rings and scale rings. The dimension of this lens is 30% smaller than our conventional models.
This lens incorporates 2 FLD (“F” Low Dispersion) glass elements, which have performance equal to fluorite, 1 SLD (Special Low Dispersion) glass element and 3 aspherical glass lenses including double sided aspherical lens. By optimizing the power alignment of the lens, both chromatic aberration of magnification and axial chromatic aberration have been corrected. From infinity to macro, it achieves superior image quality through entire zoom range. This lens offers extraordinary expressive power and is capable of surpassing the requirement of the rigorous checking process of our new MTF measuring system “A1”.
The aperture value is F2.8 at the wide end (17mm), and is F4 at the telephoto end (70mm). The bright viewfinder aids focusing and composition of images. The fast apertures also offer useful functions such as fast shutter speeds to prevent an object from being blurred and ensuring a smooth bokeh in the background.
Sigma's own unique OS (Optical Stabilizer) function is incorporated. It offers effective correction of approximately 4 stops, which makes it possible to compensate for camera shake even in macro range photography where a small blur can be easily identified.
In order to achieve high rendering on this flagship lens, flare and ghosting were thoroughly measured from an early stage to establish an optical design which is resistant to strong incident light such as backlight. The Super Multi-Layer Coating reduces flare and ghosting and provides sharp and high contrast images even in backlit conditions.
The 7 blade-rounded diaphragm creates an attractive blur to the out-of-focus areas of the image.