The Sigma 20mm F1.4 DG DN Art is a lightweight (635g) wide-angle, full-frame prime lens for Sony mirrorless cameras that is perfect for astrophotography. It delivers outstanding Art-line optical quality and offers a range of advanced features. As well as being very well-suited to astro, this 20mm F1.4 is an ideal optic for landscapes, interiors and a range of other wide-angle applications. It includes a number of important features including a manual aperture ring with de-click and lock functionality, a front filter thread and rear filter holder, a Lens Heater Retainer to hold a heat strip in position, and an all-new Manual Focus Lock switch to fully deactivate the focus ring. The optical performance of the lens is exceptional, with ultra-sharp results across the entire frame even at F1.4, and very well controlled sagittal coma flare essential for astrophotography. The bright aperture is perfect for night sky landscapes, as well as for hand-held low-light shooting and for achieving a shallow depth-of-field. Outstanding optical performance The lens is constructed with 17 elements arranged in 14 groups, including two SLD elements and three aspherical elements, one of which is the largest double-sided aspherical element ever produced by Sigma. This advanced optical design rigorously suppresses a range of optical aberrations, such as sagittal coma flare and chromatic aberration, and ensures pin-sharp results right across the frame even wide-open at F1.4. Advanced functionality The 20mm F1.4 DG DN | Art includes a front filter thread in spite of its very large F1.4 aperture and ultra-wide angle-of-view. The lens also comes with a rear filter holder, giving photographers the freedom to more easily combine multiple filters. This is particularly useful for astrophotographers, who may want to attach a light pollution filter at the front and a soft filter at the rear. The lens has an aperture ring built in, which is de-clickable for a smooth transition between aperture settings useful for changing exposure seamlessly during video shooting. The aperture ring also has a lock switch. A new Manual Focus Lock (MFL) switch completely deactivates the focus ring, ensuring the focus position wont change if it is accidentally knocked. So for night-sky photographers, the days of using tape the hold the focus ring in position are over. Another new feature designed with astrophotographers in mind is the Lens Heater Retainer, which is a pronounced lip around the front element to keep a heat strip firmly in place. Heat strips are commonly used to stop condensation forming on the elements when working at night. An AFL button is built into the lens, which can be customized to a range of different functions. Superb build quality The robust body is built from a combination of aluminum and Thermally Stable Composite (TSC), giving it a sleek finish, and the focus ring has a smooth, well damped action. A petal-shaped lens hood is included, and equipped with a lock mechanism to keep it securely fastened to the lens. A rubber grip makes it easier to attach and remove the hood. Built with a dust and splash-resistant structure, a water- and oil-repellent coating on the front element, and a rubber seal around the mount, the 20mm F1.4 DG DN is safe to use during longer outdoor shoots. Features at a glance: - Lens construction: 17 elements in 15 groups, with 2 FLD and 3 aspherical lens elements - Internal focus system - Compatible with high-speed autofocus - Stepping Motor - Compatible with Lens Aberration Correction - Support for DMF and AF+MF - Compatible with AF Assist - Super Multi-Layer Coating - Nano Porous Coating - Water and oil-repellent coating - Focus Mode Switch - Lens Heater Retainer - Aperture Ring - Aperture Ring De-click Switch - Aperture Ring Lock Switch - AFL Button - MFL Switch - Rear filter holder - Petal-type lens hood (LH756-01) - Mount with dust and splash-resistant structure - 9-blade rounded diaphragm - High-precision, durable brass bayonet mount - Made in Japan craftsmanship | Sigma Unisex AF F1.4 DG DN Art Lens - Sony E-mount in Black | Size: 20mm