Sony SLT-A77VM 2011 α Lens and Lens Accessory Brochure and Specifica - Page 7

Hoods and filters Without lens hood (flare, poor contrast) With lens hood (no flare, high contrast) Visible ghosts How lens hoods work Extraneous light Enlarged view No ghosts Light needed for image formation Lens hood 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. Without circular PL filter (reduced contrast) Without ND filter 12 Petal hood Round hood With circular PL filter (increased contrast and deep saturation) 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. With ND filter (reduced light for slower shutter speed) 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. 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 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. Protar® (1890-) Planar® (1896-) Tessar® (1902-) Sonnar® (1929-) 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 highrefractive-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. 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. Carl Zeiss coated lens Uncoated lens Light source Image sensor Light source Image sensor Reduced reflection Uncontrolled reflection 13