Not only will the 20mm (30mm in 35mm full-frame format) focal length and F2.8 maximum aperture appeal to experienced photographers, but the outstanding resolution of this lens will satisfy their most stringent image quality requirements as well. Three aspheric elements help to achieve superb contrast and resolution right out to the image edges, while simultaneously enabling a compact 20.4 mm-thick pancake design that makes for a portable combination with compact E-mount cameras.
When changing your aperture to defocus the background, the light sources appear blurred. This ‘bokeh’ effect of the blurred background can be enhanced with circular aperture blades used in this lens. Conventional aperture blades have flat sides creating unappealing polygonal shaped defocussed points of light. α lenses overcome this problem through a unique design that keeps the aperture almost perfectly circular from its wide-open setting to when it is closed by 2 stops. Smoother, more natural defocusing can be obtained as a result.
Aspherical lens design dramatically reduces spherical aberration while also reducing lens size and weight. Spherical aberration is a slight misalignment of the light rays projected on the image plane. This is caused by differences in refraction at different points on conventional spherical lenses which degrade image quality in large-aperture lenses. Specially shaped “aspherical” elements near the diaphragm restore alignment of light rays at the image plane, maintaining high sharpness and contrast even at maximum aperture and can also be used at other points in the optical path to reduce distortion. Well-designed aspherical elements can reduce the total number of elements required in the lens, thus reducing overall size and weight. Advanced Aspherical (AA) elements are an evolved variant, featuring an extremely high thickness ratio between the center and periphery. AA elements are exceedingly difficult to produce, relying on the most advanced molding technology to consistently and precisely achieve the required shape and surface accuracy, resulting in significantly improved image accuracy and quality.
Only the rear groups of the optical system move to focus the lens, which allows for speedy AF operation and a shorter minimum focusing distance. Since the front of the lens does not rotate, operability is improved when shooting with a polarizing filter attached.
