Spherical aberration is a slight misalignment of light rays projected on the image plane by a simple spherical lens, caused by differences in refraction at different points on the lens. That misalignment can degrade image quality in large-aperture lenses. The solution is to use one or more specially shaped “aspherical” elements near the diaphragm to restore alignment at the image plane, maintaining high sharpness and contrast even at maximum aperture. Aspherical elements 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, thus reducing overall lens size and weight.

Aspherical lenses are much more difficult to manufacture than simple spherical types. New XA (extreme aspherical) lens elements achieve extremely high surface precision that is kept to within 0.01 micron by innovative manufacturing technology, for an unprecedented combination of high resolution and the most beautiful bokeh you've ever seen.

Advanced Aspherical (AA) elements are an evolved variant, featuring an extremely high thickness ratio between the centre and periphery. AA elements are exceedingly difficult to produce, depending on the most advanced moulding technology available to consistently and precisely achieve the required shape and surface accuracy. The result is significantly improved reproduction and rendering.

An ED aspherical element is an aspherical lens element manufactured from ED (Extra-low Dispersion) glass. ED glass effectively suppresses colour aberration while an aspherical profile can accurately compensate for a range of optical aberrations including spherical aberration, coma and distortion. Because ED aspherical element combines the functions of ED glass and an aspherical profile in a single element, they can be used to make compact, lightweight lenses that deliver high optical performance.

"In a conventional lens, the amount of light collected at the periphery of the lens is roughly equal to the amount of light at the centre. This results in uniformly sharp dots at points "b" and "c" below. However, a special filter called an "apodization optical element" collects less light at the lens periphery, which results in diffusion at the edges of the dots instead. Smoother defocusing is obtained due to this optical characteristic.

T numbers
Because the STF lens with the apodization optical element collects less light overall than conventional lenses, F-stops are replaced by T (transmission) numbers. In practice, the two types of values can be used interchangeably to determine exposure."

Original Sony Nano AR Coating technology produces a lens coating that features a precisely defined regular nano-structure that allows accurate light transmission while effectively suppressing reflections that can cause flare and ghosting. The reflection suppression characteristics of the Nano AR Coating are superior to conventional anti-reflective coatings, including coatings that use an irregular nano-structure, providing a notable improvement in clarity, contrast, and overall image quality.

A new Nano AR Coating II that can be evenly applied to large lens elements or highly curved element surfaces has been developed to suppress internal reflections that can cause flare and ghosting, for clear, crisp imagery. Despite the lens’s wide angle of view, Nano AR Coating II maintains high clarity and contrast throughout the entire image, even in difficult light.

The exposed front element of any lens can pick up water, mud, oil, fingerprints and other contaminants that can not only compromise image quality, but in some cases even damage the lens. Sony provides a potent solution with a fluorine front-element coating that results in a greater liquid contact angle, reducing the lens's wettability and effectively "repelling" contaminants. Any water-based or oil-based grime that does become attached to the lens can be easily wiped away. In addition to protecting valued lenses, the fluorine coating reduces the need to worry about keeping lenses clean in the field.

The fact that lens-coating technology — vapor deposition of a thin, even coating on the lens surface to reduce reflections and maximize transmission — was originally a ZEISS patent is well known. The ZEISS company also developed and proved the efficacy of multi-layer coatings for photographic lenses, and this is the technology that became the T* coating.

Until the introduction of coated lenses, the lens surface would reflect a large percentage of the incoming light, thus reducing transmission and making it difficult to use multiple elements in lens designs. Effective coatings made it possible to design more complex optics that delivered significantly improved performance. Reduced internal reflection contributed to minimum flare and high contrast.

The ZEISS T* coating is not simply applied to any lens. The T* symbol only appears on multi-element lenses in which the required performance has been achieved throughout the entire optical path, and it is therefore a guarantee of the highest quality.

Although most of the light that falls on an optical glass transmits right through, some of it reflects at the surface of the lens to cause flare or ghost images. In order to avoid this problem, a thin layer of anti-reflective coating must be applied to the lens surface. α lenses use exclusive multi-layered coating to effectively suppress such problems over a wide spectrum of wavelengths.

Only the middle or rear groups of the optical system are moved to achieve focusing, which leaves the total length of the lens intact. Benefits include fast autofocusing and a short minimum focusing distance. Also, the filter thread at the front of the lens does not rotate, which is convenient if you’re using a polarizing filter.

SMO (Smooth Motion Optics) is a Sony optical design concept for interchangeable lenses that is specifically aimed at achieving the highest possible image quality and resolution for motion images.

SMO design addresses three main issues that are critical for moviemaking:

- Focus breathing (angle of view instability while focusing) is effectively minimized by a precision internal focus mechanism.

- Small focus shifts that can occur while zooming are eliminated by a special tracking adjustment mechanism.

- Lateral movement of the optical axis while zooming is eliminated by an internal zoom mechanism that keeps the length of the lens constant at all focal lengths.

The level of precision required demands both exacting design and constant monitoring during manufacture, but the benefits for moviemaking with large aperture lenses, particularly on large format sensors, are spectacular and well worth the effort.

A type of lens zooming method. The benefit of the internal zoom is that the length of the lens remains constant while zooming, and the barrel does not rotate so polarizers and other position-dependent filters can be used without the need for additional support.

Linear Response MF refines controls for manual focusing operability. The focus ring features high control resolution so that user input is precisely followed when focusing manually. Linear Response MF also realizes intuitive focusing and is almost equivalent to mechanical manual focusing. The focus changes linearly in response to focus ring rotation, giving the user the control immediacy needed for fast, accurate manual focusing.

The floating focus mechanism achieves consistent high resolution from infinity to the closest focusing distance. This system helps to reduce all types of aberration to minimum levels and thereby maintain sharp, high-resolution rendering from infinity focusing for landscapes, for example, all the way down to close-up focusing for portraits and similar subjects.

The XD (extreme dynamic) Linear Motor has been developed to deliver higher thrust and efficiency than previous types, in order to make the most of the rapidly evolving speed performance of current and future camera bodies. Linear motor design and component layout have been thoroughly revised to achieve significantly higher thrust.

RDSSM is a piezoelectric motor that contributes to smooth and silent AF operation. The motor produces high torque at slow rotation, and provides immediate start and stop responses. It is also extremely quiet, which helps keep autofocusing silent. Lenses that feature RDSSM also include a position-sensitive detector to directly detect the amount of lens rotation, a factor that improves AF precision overall.

Specially designed linear motors provide direct, contactless electromagnetic drive of the lens focus group for extremely quiet, responsive operation. The quiet operation, fast response, and precision braking provided by the contactless linear drive system are not only an advantage for still photography, but offer the type of smooth, silent operation required by moviemakers as well. 

A stepping motor (STM) is a motor with a mechanism that divides the rotational operation into a number of steps for controlled rotation. It rotates one step each time it receives an electrical pulse. The STM allows the lens to focus smoothly and quietly when shooting photos and movies.

The iris/aperture ring allows intuitive aperture control. It provides seamless aperture control for outstanding usability.

An iris/aperture ring provides the type of immediacy and response that professionals need for both still photography and videography. A Click ON/OFF switch allows the aperture ring click stops to be engaged or disengaged as required. Engaging the click stops provides tactile feedback that can make it easier to gauge how much the ring has been adjusted by feel and is, therefore, a good choice for still photography. When the click stops are disengaged, the aperture ring moves smoothly and quietly, providing seamless, silent control for moviemaking.

Switchable zoom ring direction. A simple mechanical operation is all that is required to switch the direction of the zoom ring to match individual user preferences. Zoom ring direction can be easily switched as required.

The provided Optical SteadyShot modes make it more convenient to capture sharp images in handheld shooting under various conditions. For example, Mode 2 stabilization facilitates dynamic panned shots and Mode 3 provides a more stable viewfinder image that makes tracking and framing easier.

The provided Optical SteadyShot modes make it more convenient to capture sharp images in handheld shooting under various conditions. For example, Mode 2 stabilization facilitates dynamic panned shots, and Mode 3 provides optimum stabilization for tracking and shooting dynamic, unpredictable sporting action.

The lens is designed to be dust- and moisture- resistant, ensuring reliable operation when shooting outdoors in challenging conditions.

In general, if an aperture uses 7, 9 or 11 aperture blades, then the shape of the aperture becomes a 7-sided, 9-sided or 11-sided polygon as the aperture is made smaller. However, this has a certain undesirable effect in that the defocusing of point light sources appears polygonal and not circular. 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.