Sony SLT-A77VM 2011 α Lens and Lens Accessory Brochure and Specifica - Page 9
lens technology
View all Sony SLT-A77VM manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 9 highlights
a lens technology The technology required to produce first-class interchangeable camera lenses is very sophisticated indeed, and that applies to every phase of the production process from design through precision parts manufacturing and assembly to stringent quality assurance testing and more. Sony brings a distinguished history of excellence in all of these areas to bear in producing the a lenses. You'll feel the difference in the way a lenses handle, and you'll see the difference in the superior image quality they deliver. Aspherical lens elements Spherical aberration, slight misalignment at the image plane between light that has passed through the center and periphery of a simple spherical lens, can become a noticeable problem in large-aperture lenses. The most effective solution is to use one or more specially shaped aspherical elements near the aperture stop to restore perfect alignment at the image plane, thus maintaining high contrast even with the aperture wide open. Aspherical lenses arranged far from the aperture stop can minimize image distortion and flatness of the image plane. Well-designed aspherical lens can reduce the number of elements in the lens for less overall size and weight. Spherical lens Aspherical lens ED and Super ED glass Chromatic aberration in conventional optical glass elements can reduce contrast, resolution, and color fidelity, particularly at longer focal lengths. ED (Extra-low Dispersion) and Super ED glass were developed with refractive index and dispersion characteristics specially tailored to counter this problem. Lenses that include ED or Super ED glass elements provide superior contrast and resolution throughout the image even at large aperture settings. Conventional glass ED glass Super ED glass Image sensor plane Image sensor plane Image sensor plane Image sensor plane Image sensor plane Auto clutch The auto clutch mechanism decouples the focus ring so that it does not rotate during autofocus operation. This allows the lens to be cradled in one hand without interfering with autofocus operation, for improved shooting comfort and versatility. Circular aperture Standard lens apertures appear as a flat-sided polygon when the lens is stepped down, the number of sides corresponding to the number of blades in the aperture.This results in the familiar polygonal out-of-focus highlights seen in many photographs. Almost all a lenses feature a unique circular aperture that contributes to smooth, natural defocusing. Comparison of aperture design Conventional aperture Circular aperture Floating lens mechanism This focusing feature is particularly important in certain lenses that are designed for close focusing. It maintains optimum lens performance and therefore maximum sharpness right down to the minimum focusing distance by moving "floating" elements independently when focusing, rather than moving the entire optical assembly as a whole. Focus hold button Press this button to lock focus at the current setting. The focus hold button is on the lens barrel right under your fingertip for convenient, fast operation. Focus range limiter This feature can be used to limit focus range when you need the quickest possible autofocus response. On some lenses a single "limit" range will match the characteristics of the lens (near focus limit on macro lenses, for example), while some lenses have a "near/far" limit range switch. 16 Internal focusing mechanism In this type of lens, focusing is achieved by moving only the internal elements. The overall length of the lens remains constant, and the filter mounting thread at the front of the lens remains stationary during focusing.The latter characteristic is an advantage when using a polarizing filter. Other advantages include fast autofocus response and reduced minimum focusing distances. SAM (Smooth Autofocus Motor) SAM is another type of internal lens motor for autofocus drive. While the SSM motor described above is piezoelectric, the SAM motor is electromagnetic in operation, but provides similar benefits: responsive autofocus operation that does not require mechanical coupling from the camera body. Rear focusing mechanism This focusing configuration has similar advantages to internal focusing, described above, but focusing is achieved by moving the rear lens elements rather than the internal elements. SSM (Super Sonic wave Motor) SSM is an advanced direct-drive piezoelectric motor that is capable of delivering high torque even at low speeds, with almost instantaneous start/ stop response. Its fast response and low-noise operation translate directly into quick, quiet autofocus operation. SSM lenses also include position detection for enhanced focusing precision. Other advantages of this advanced drive system are that the focus ring does not rotate during autofocus operation, and you can directly switch to manual focusing by simply rotating the focus ring. STF lens A unique a lens feature currently available only in the SAL135F28, STF (Smooth Trans Focus) is an optical technology that is aimed specifically at creating the smoothest, most visually pleasing defocusing effect possible while retaining full resolution and contrast at in-focus areas. STF technology employs a special "apodization" element that causes the intensity of defocused point light sources to fade out radially so that no sharply defined edges or geometry remain.The result is extraordinarily creamy defocusing that goes beyond the capabilities of conventional lens technology. STF lens Apodization optical element A a b c Rotor Stator AC voltage, Phase B AC voltage, Phase A Piezoelectric element Stator Rotor SSM consists of a rotor (left), and a stator (right) on which plexoelectric elements are mounted. Conventional lens A Defocusing of STF lens (around focus point "a") a b c Defocusing of conventional lens (around focus point "a") 17