Sony DSLR-A300K Brochure and Specifications | Page 7

Sony Cameras Brochure and Specifications - DSLR-A300K.
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Use your lens hood!

The lens hoods provided with most interchangeable-lenses are not just 
accessories to be used occasionally. They are an important part of the lens’s 
optical system and should always be used in order to ensure optimum 
performance. There are exceptions, such as when an on-camera flash is 
used and the lens hood casts a shadow, but for most shooting situations  
the lens hood should be on the lens, not in your bag. If your lens has a  
built-in extending hood, it should be extended when you’re shooting.

Even though a lenses are uncompromisingly designed with multi-coated 
elements and other internal features that minimize flare and ghosting, these 
problems can still occur if extraneous light is allowed to enter the lens. And 
although the effects of flare might not be obvious in all images, it can subtly 
degrade contrast and prevent you from capturing the strongest possible 
image. Strong backlighting, particularly near the edge of the image, can 
cause ghosts even when a lens hood is used. In such situation the only 
solution is to reframe the shot so that the problematic light source is excluded.

Lens hoods block extraneous light

Any light entering the lens that does not come directly from the scene being 
photographed is extraneous light that needs to be eliminated. Light that 
grazes the front element at a steep angle or bounces around inside the lens 
barrel will degrade image quality. A lens hood that is properly designed for 
the lens on which it is used will effectively block extraneous light that does 
not contribute directly to the image, ensuring that the lens will deliver the 
highest resolution and contrast it is capable of. Although most lens hoods 
for normal to telephoto focal lengths are basic round designs, lens hoods 
for wide angle lenses often have a “petal” shape that is designed to block 
unwanted light without intruding into the corners of image area.

Visible ghosts

Protar® 

(1890-)

Planar® 

(1896-)

Tessar® 

(1902-)

Sonnar® 

(1929-)

Uncoated lens

Carl Zeiss coated lens

Carl Zeiss® optics
For many photo enthusiasts, Carl Zeiss lenses have long been the ultimate 
choice. Many models are available, but the only autofocus Zeiss lenses 
currently available for use on interchangeable-lens digital cameras are 
those that have been created through close cooperation between Carl Zeiss 
AG and Sony for the a series cameras.

The unmatched T* (T-star) coating

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 Carl Zeiss patent is well known. The Carl 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 Carl 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.

The scientific approach

It was Ernst Abbe of Carl Zeiss AG who first 
applied scientific principles to lens design, rather 
than relying on trial-and-error experience. A 
significant portion of the history of photographic 
lens development centers on the Protar, Planar 
and Sonnar designs that featured advanced 
optical paths based on those principles. In many 
ways the history of Carl Zeiss AG is the history  
of photographic lenses.

Hoods and filters

Neutral density filters

Sometimes the light is so bright that you’re forced to use smaller apertures or 
faster shutter speeds than you want to. Neutral density (ND) filters reduce the 
amount of light entering the lens without affecting the color or tonal balance 
in any way, and can be very useful in this type of situation. Suppose you 
want to shoot a waterfall using a shutter speed that’s slow enough to blur the 
moving water and create a sense of motion, but the lighting at the scene is 
too bright. An ND filter will reduce the light intensity so that you can use the 
relatively slow shutter speed required to achieve the desired effect.

Circular polarizing filters for  

improved contrast and color

Circular polarizing (PL) filters can be used to eliminate reflections and glare  
from reflective surfaces such as glass and water, but landscape photographers 
find them most useful for increasing contrast and saturation in skies, foliage and 
other icons of the landscape genre. In all cases the filter works by eliminating 
reflections, but in the latter, it is eliminating reflections from airborne dust and 
water vapor, thus removing a veil of glare and allowing the true colors of the 
scene to come through.

Light source

Light source

Reduced reflection

Uncontrol ed reflection

Image sensor

Image sensor

Without lens hood (flare, poor contrast)

Extraneous light

Lens hood

Without ND filter 

With ND filter 

(reduced light for slower shutter speed)

Enlarged view

No ghosts

With lens hood (no flare, high contrast)

Petal hood

Round hood

Without circular PL filter 

(reduced contrast)

With circular PL filter 

(increased contrast and deep saturation)

Light needed for 
image formation

How lens hoods work

The Carl Zeiss lenses that started it all

Protar
Developed by Dr. Paul Rudolph in 1890, this 
lens was one of the original Anastigmat series. 
The design was named “Protar” (from the Latin 
“proto,” or “first”/”origin”) in 1900. The front 
group was a standard achromatic combination 
of low-refractive-index crown glass and high-
refractive-index flint glass, but the rear group 
was an innovative achromatic doublet using 
Jena glass, with high-refractive-index crown 
glass and low-refractive-index flint glass. The front 
and rear elements were located on either side 
of the diaphragm, 
effectively suppressing 
chromatic aberration. 
This design evolved to 
become the Unar lens 
and later the Tessar.

Planar
Another Paul Rudolph design, developed in 1897. 
Initially this design was called the “Anastigmat 
Series IA.” It features a symmetrical 6-element 
4-group Gaussian design that facilitates the use 
of large apertures. The “Planar” name is derived 
from the flatness of the image. Planar lenses are 
appreciated for their superb image depth and 
rich color reproduction.

The Carl Zeiss traditions of innovative technology 
and uncompromising quality are alive in 
today’s a series lenses as well.

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