Nano AR Coating
Effectively suppress reflections that can cause flare and ghosting with Sony's original Nano AR Coating technology. This precisely defined regular nano-structure allows accurate light transmission, contributing to high-quality images, even more so than lenses with coatings that use an irregular nano-structure. The reflection suppression characteristic of the Nano AR Coating is superior to conventional anti-reflective coatings, providing a notable improvement in clarity, contrast, and overall image quality.
Circular Aperture
When 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.
Aspherical lens elements
Aspherical lens design dramatically reduces spherical aberration while also reducing lens size and weight. Spherical aberration is a slight misalignment of the light rays projected on the image plane. This is caused by differences in refraction at different points on conventional spherical lenses which degrade image quality in large-aperture lenses. Specially shaped "aspherical" elements near the diaphragm restore alignment of light rays at the image plane, maintaining high sharpness and contrast even at maximum aperture and can also be used at other points in the optical path to reduce distortion. Well-designed aspherical elements can reduce the total number of elements required in the lens, thus reducing overall size and weight.
Internal focusing
Only the middle groups of the optical system move to achieve focus, so the overall length of the lens does not change. Other important benefits include fast autofocusing and a short minimum focusing distance. Also, the filter thread at the front of the lens does not rotate, which is convenient if you're using a polarizing filter.
Focus hold button
Once you've adjusted focus to where you want it, pressing this button on the lens barrel will keep the lens locked to that focusing distance. The preview function can also be assigned to this button through the camera's custom settings.
Focus range limiter
This function allows you to set a limit on the focusing range which can save you time during AF operation as the lens will not 'hunt' through the entire focusing range. In macro lenses, this limit can be on either the near or far range (as pictured). In the SEL90M28G, the limit is set on far ranges only.
Sliding Focus Ring
The focus ring slides back and forth to select manual or auto focus which together with a focus hold button, inner focus, and a focus range limiter provide optimum control for macro photography making it easier to shoot insects and other subjects that cannot be approached too closely. Minimal focus breathing and quiet operation are also advantageous for shooting movies.
Lens-based optical image stabilization
Gyro sensors built into the lens detect even the slightest movement, and the stabilization lens is precisely shifted to counteract any image blur that might occur. The use of precision, quiet linear motors and technology inherited from high-end Sony professional camcorders results in exceptionally quiet, effective image stabilization that contributes to high-quality movies as well as stills.
Direct Drive SSM (DDSSM) for quiet, precise focusing
Quiet, precise DDSSM (Direct Drive SSM) focus drive - employs piezoelectric elements oscillating at ultrasonic frequencies to drive the focus lens groups. In this case two floating focus groups are driven by independent DDSSM systems for precision positioning of the relatively heavy lenses required for macro photography. The DDSSM drive system is remarkably quiet, making it ideal for animal and insect photography, as well as for movies. It also improves the precision of "focus wobble" employed to achieve optimum focus when shooting movies.
