Sony DSLR-A700P Lenses and Accessories Selection Guide - Page 8

STF (Smooth Trans Focus) Lens Reflex Super-Telephoto Lens SAL135F28 Manual focus only Teleconverter compatible 135mm F2.8 [T4.5] STF • Lens groups/elements: 6/8 (includes 1 group with 2 APD elements) • Minimum focus: 34-1/4" (0.87 m) • Filter diameter: 72 mm • Size: (diameter x length): 3-1/8 x 3-7/8" (80 x 99 mm) • Weight: 1 lb 9.7 oz (730 g) The special-purpose lens allows you to create truly unique images with exceptionally smooth transitions between in-focus and defocused areas. This is achieved through apodization optics, which gives your images added dimensionality and also contributes to the natural spread of highlights. Clarity at the point of focus is superb, and vignetting and double-line defocusing are avoided. A separate manual aperture ring gives you added control over defocusing of objects at the edges of the image. SAL135F28 (135mm F2.8 [T4.5] STF) Ideal Defocusing with the STF Lens In a conventional lens, the amount of light collected at the periphery of the lens is roughly equal to the amount of light at the center. This results in uniformly sharp objects at points b and c, below. The STF lens, however, uses a special filter called an "apodization optical element" that collects less light at the lens periphery, which results in diffusion at the edges of the objects instead. Smoother defocusing is due to this optical characteristic. Conventional lens A a STF lens Apodization optical element A a bc bc Defocusing of conventional lens (around focus point "a") Defocusing of STF lens (around focus point "a") STF Lens & T Numbers Because the STF lens collects less light overall than conventional lenses, F-stops are replaced by T (transmission) numbers. In practice, the two types of values can be used interchangeably to determine exposure. 14 SAL500F80 500mm F8 Reflex • Lens groups/elements: 5/7 (includes 1 filter) • Minimum focus: 151-1/2" (4.0 m) • Filter diameter: 42 mm (rear slide-in type) • Size: (diameter x length): 3-1/2 x 4-5/8" (89 x 118 mm) • Weight: 1 lb 7.5 oz (665 g) A unique reflex lens that provides autofocusing through the innovative combination of a mirror lens system and the camera's AF sensor. Captures impressively clear images with none of the chromatic aberration that often mars conventional refractive lenses, and produces distinctive ring-shaped defocusing effects. Light and compact for a super-telephoto lens, and thus an ideal option for nature and wildlife photography, especially as a means of minimizing gear. Includes focus hold button. SAL500F80 (500mm F8 Reflex) Autofocusing in a Reflex Telephoto Lens In AF operation, distance is usually measured with a beam of light that transmits through the lens at around F6.7 to F8. If the aperture is any smaller, then AF cannot function. However, the SAL500F80 overcomes this limitation by using a modified optical design in combination with the camera's highly sensitive AF sensor. First, the secondary mirror was reduced in size so as not to obstruct the metering light. Next, the primary mirror was enlarged to improve light collection efficiency. Finally, aberrations were corrected at the rear of the lens to ensure high sharpness while also enabling AF. Secondary mirror Primary mirror Sensor position (equivalent) Image sensor for AF Detail of AF sensor Exit pupil of 500mm lens Condenser lens Separator lens Light beam required for AF Icons: Circular aperture Internal focusing Focus Hold Button Focus Range limiter ADI flash metering SSM (Super sonic wave motor) • For details, please refer to the Lens Technology section on p.26-28. 15