Sigma 30mm f/1.4 EX DC HSM lens

The Sigma 30mm 1.4 EX DC HSM is a wide-aperture photographic lens made by the Sigma Corporation, equipped with a Hyper Sonic Motor. The lens was produced in Canon EF mount, Four Thirds System, Nikon F-mount, Pentax K mount, the SA mount, and the Sony/Minolta AF Mount varieties, all of the same optical formula. It shipped with a removable petal-type lens hood. The lens assumes a crop factor of roughly 1.5, and therefore the image circle will not cover the full frame if used on full-frame or 135 film cameras.
In 2013, Sigma announced that the lens would be replaced by a redesigned model designated as the Sigma 30mm 1.4 DC HSM A; the new lens went on sale in March of that year in Canon, Nikon, and Sigma mounts.
Its large aperture allows for a shallow depth of field, allowing good isolation of close subjects. On APS-C sensor cameras, its field of view equivalent to that of a 46mm lens, 48mm lens, 51mm lens or 60mm lens. On the Four-Thirds mount, it is the only affordable normal, large aperture lens, therefore it is popular lens on that format.

Optical properties

The Sigma 30mm 1.4 EX DC HSM lens has unusual optical properties. With most photographic lenses, vignetting is drastically reduced by stopping down the aperture by about 1 f-stop. This lens has a more linear response to stopping down the aperture. To reduce vignetting by about one half, it is required to stop down the aperture by over 3 full f-stops. The optical resolution properties of this lens are also unique. Most lenses are typically sharp in the center of the image frame, and softer in the edges. This problem is typically solved by stopping down the lens. This lens has little response to such an effort. When stopped down by over 4 stops, the edges of the frame are still soft. However, the center resolution of the lens is high when used wide open, and becomes exceedingly high when the lens is stopped down.