From the ManufacturerDT 55-200mm F4-5.6 SAM Zoom LensThis superb telephoto zoom lens for your α DSLR camera has a smooth and silent AF operation with built-in motor to handle themed range to telephoto zoom shots. In 35mm equivalent, it covers midrange 82.5mm to 300mm telephoto zoom (4x) ideal for shooting portraits, sports, wildlife and more. An excellent all-around lens. Please note: DT lenses are not recommended for use with the DSLR-A900. Technology Circular ApertureWhen changing your aperture to defocus the background, the light sources appear blurred. This ‘bokeh’ effect of the blurred background can be enhanced with circular aperture blades used in this lens. Conventional aperture blades have flat sides creating unappealing polygonal shaped defocussed points of light. α lenses overcome this problem through a unique design that keeps the aperture almost perfectly circular from its wide-open setting to when it is closed by 2 stops. Smoother, more natural defocusing can be obtained as a result. ED (Extra-low Dispersion) glassAs focal lengths get longer, lenses built with conventional optical glass have difficulties with chromatic aberration, and as a result images suffer from lower contrast, lower color quality, and lower resolution. ED glass dramatically reduces chromatic aberration at telephoto ranges, and provides superior contrast across the entire image, even at large aperture settings. Super ED glass provides enhanced compensation for chromatic aberration. Distance encoderThe distance encoder plays an integral part in ADI flash metering, which delivers high precision flash metering that is unaffected by the reflectance of subjects or backgrounds. The distance encoder is a lens component that directly detects the position of the focusing mechanism, and sends a signal to the CPU in order to measure distance to the subject. During flash photography, this data is very useful in calculating how much flash output is appropriate to the scene. SAM (Smooth Autofocus Motor)Rather than using the focus drive motor in the camera body, SAM lenses feature an autofocus motor built into to the lens itself that directly drives the focusing element group. Since the built-in motor directly rotates the focus mechanism, operation is significantly smoother and quieter than conventional coupled autofocus drive systems.2009 Sony Electronics Inc. All rights reserved. Reproduction in whole or in part without written permission is prohibited. Sony, α and HDNA, are trademarks of Sony. All other trademarks are trademarks of their respective owners. Non-metric weights and measurements are approximate and may vary.