Sony LA-EA1 Brochure and Specifications | Page 9

Sony Cameras Brochure and Specifications - LA-EA1.
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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.

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.

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.

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.

A

A

a

a

b

b

c

c

Apodization optical element

Defocusing of STF lens

(around focus point “a”)

Defocusing of conventional
lens (around focus point “a”)

STF lens

Conventional lens

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.

Conventional glass

Spherical lens

Conventional aperture

Circular aperture

Image 
sensor 
plane

Image 
sensor 
plane

Aspherical lens

ED glass

Super ED glass

Image sensor 
plane

Image sensor 
plane

Image sensor 
plane

Comparison of aperture design

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.

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.

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.

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.

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.

SSM consists of a rotor (left), and a stator (right) on which plexoelectric 
elements are mounted.

16

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Piezoelectric 
element
Stator
Rotor

Rotor

Stator

AC voltage, 
Phase B
AC voltage, 
Phase A

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