Sony SLT-A77VM Specyfikacje - Strona 9

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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

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

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

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.

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.

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.

Image sensor

plane

Rotor

Stator

SSM consists of a rotor (left), and a stator (right) on which plexoelectric

elements are mounted.

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.

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

Piezoelectric

element

Conventional lens

AC voltage,

Stator

Phase B

Rotor

AC voltage,

Phase A

Defocusing of STF lens

(around focus point "a")

Defocusing of conventional

lens (around focus point "a")