Three years ago today in 2010, a large aperture standard zoom lens with a minimum focal length of 17mm, designed exclusively for digital SLR cameras and incorporating Sigma’s original OS (Optical Stabilizer) —17-50mm F2.8 EX DC OS HSM was put on the market. We’d now like to introduce the attraction of this 17-50mm F2.8 standard lens which was aimed at large aperture.

Historical Background
As a DSLR exclusive large aperture standard lens, the minimum focusing distance of 18-50mm F2.8 EX DC OS HSM released August 2004, was shorten to be 18-50mm F2.8 EX DC MACRO released October 2006. Following the release of the 18-50mm F2.8 large aperture standard zoom lens featuring Optical Stabilizer (OS) lens system, 18-50mm F2.8-4.5 DC OS HSM and 17-70mm F2.8-4 DC MACRO OS HSM was released in May and December 2009 in succession. Therefore, the new model of 18-50mm F2.8 incorporated Optical Stabilizer (OS) was expected.
The feature of the lens
17-50mm F2.8 EX DC OS HSM is the lens based on 18-50mm F2.8 EX DC MACRO. This particular lens was incorporated Optical Stabilizer (OS) and the focusing length was extended from 18mm to 17mm. In addition to the rear aspheric glasses, the lens is also incorporated the OS system to ensure the low performance won’t occur. Overall, the incorporation of Optical Stabilizer and the use of FLD (“F” Low Dispersion) glass elements provide excellent correction for all types of aberrations throughout the whole range of the focusing length and ensure the ultra-high performance. Furthermore, as a large aperture standard lens featuring Optical Stabilizer (OS), it has a compact construction with an overall length of 91.8mm.
The difficulty in development
Considering the vignetting at the edge of the image field when the focusing length was extended from 18mm to 17mm was a big challenge. It is difficult to ensure the brightness at the edge of the image field, and the representation of large-sized filters and semi-diameter of product are required.
However, there was some possibility to lose the convenience of this compact-sized lens even the vignetting was assured. Therefore, lens configurations must take this into account.
Therefore, to solve these problems, it was decided that the optical design of incorporated FLD glasses would be redesigned. The challenge included not to increase one more size from 18-50mm F2.8 EX DC MACRO and not to over enlarge the semi-diameter of product as long as brightness was ensured.
The trait to be impressive
The challenge in redesigning this lens would be how to show a large aperture F2.8 throughout focusing range lens equipping Optical Stabilizer (OS) manufactured in superior lever over existing optical performance without changing the size.
From lens designer
This large aperture F2.8 standard lens equipping Optical Stabilizer (OS) is ideal for low light scene such as indoor shot or sunset. Besides, you can also enjoy the beautiful blurred background with this large aperture F2.8 throughout the zoom range lens.
Give it a try
SIGMA has achieved this ease-of-use lens. It is worth to take a trial on this never uncompromised designed lens.
▽Find out more at http://www.sigma-photo.co.jp/english/lens/standard/17_50_28/