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The meaning of some abbreviation
What is APO ?
An Apochromat lens, which keeps color aberration to a minimum, using Special Low Dispersion glass is called an APO series lens at Sigma. As the refractive index of glass depends on the wavelength of the light, color aberration occurs when different colors form images at different points. This problem often occurs with telephoto lenses. In the case of normal optical glass it can only be corrected for two primary spectral colors by combination of low dispersion convex and high dispersion concave lenses. Sigma Apo lenses use SLD (Special Low Dispersion) or new ELD (Extraordinary Low Dispersion) glass to offer superior sharpness, high contrast and color correction by minimizing the chromatic aberration.
What does EX Lens mean ?
The Excellent features of these Sigma lenses such as new optical and mechanical design concept, superior performance, perfect handling, ultra compact design, durability etc., are symbolized by the EX mark.
What is DG?
These are large-aperture lenses with wide angles and short minimum focusing distances. With an abundance of peripheral illumination, they are ideal lenses for Digital SLR Cameras.
What does DC stand for?
These are special lenses designed so that the image circle matches the smaller size of most digital SLR cameras. Their specialized design gives these lense s the ideal properties for digital cameras, including compact and lightweight construction.
What is HSM?
HSM stands for "Hyper Sonic Motor". The HSM motor is driven by ultrasonic waves and it makes auto focusing, precise, silent and high-speed. Sigma's HSM version lenses are available only for AF Sigma, Canon and Nikon AF cameras.
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Questions about HSM
What is the difference between built-in HSM lens and DC-motor lens?
With conventional auto-focusing, auto-focus is driven by electromagnetic force of a DC-motor, gear and shaft mechanism. However, Ultrasonic Oscillation Energy operates the HSM lens and creates high-torque drive. Since this motor has no reduction gears, it has much quicker response to start and stop compared to DC- motor lenses. HSM system has virtually silent auto focus function, very quick responsive auto focus function and "full-time" manual focus, wherein AF can be overridden without disengaging the AF mode altogether.
Auto Focus of HSM Lens for some Nikon Cameras does not work.
The AF control system for some Nikon Cameras does not work with HSM lenses. Sigma's HSM lenses have full compatibility with F5, F4 series, F100, F90/N90, F90X/N90S, F80/N80 F70/N70, u/F65/N65,Pronea 600 and Pronea S. With other Nikon cameras, Sigma's HSM version lenses can be only used in manual focusing mode.
[ 本帖最后由 dickson 于 2009-4-28 14:13 编辑 ] |
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