SIGMA 85/1.4 DG HSM Art for SONY E-MOUNT

Ultra-high-megapixel full-frame DSLRs offering 50-megapixel or higher resolution are now available, and nothing will bring out the performance potential of these cameras better than the fundamental performance of the lens. The SIGMA 85mm F1.4 DG HSM | Art incorporates two elements made of SLD (Special Low Dispersion Glass) and one element with a high rate of anomalous partial dispersion and a high index of refraction. These features help ensure a clear image throughout the plane. The optical system also minimizes sagittal coma flare for outstanding image quality without streaking—even at wide-open aperture.

Among its new product lines, this is the fifth large-diameter F1.4 lens SIGMA has introduced for cameras with full-frame sensors. SIGMA is the only lens manufacturer that covers 20-85mm at F1.4 brightness in its lineup. This latest lens reflects our experience with this specification and insistence on offering only the best.

Elements made of SLD (Special Low Dispersion) glass and an optimized power distribution help minimize axial chromatic aberration. In the areas in front of and behind the point of focus, the optical system produces an attractive and natural bokeh effect by producing a smooth gradation of focus and minimizing streaking.

The degree to which light is refracted by glass depends on the light’s wavelength. This fact causes different colors of light to focus at slightly different points. The result is chromatic aberration, the color fringing that is particularly noticeable in telephoto lenses. Most chromatic aberration can be removed by combining a high-refractivity convex lens element with a low-refractivity concave element. Yet residual chromatic aberration known as “secondary spectrum” may still remain. To minimize this secondary spectrum, which can be a serious issue with conventional lenses, SIGMA lenses feature up to three types of exclusive low-dispersion glass offering superior performance: ELD (Extraordinary Low Dispersion), SLD (Special Low Dispersion) and FLD (“F” Low Dispersion). In particular, FLD glass offers ultra-low dispersion in combination with high transmittance and the anomalous dispersion characteristics of fluorite. Meticulous deployment of these types of exclusive low-dispersion glass and optimization of power distribution gives SIGMA lenses superlative image rendition undiminished by residual chromatic aberration.

From the start of the design process, SIGMA measured flare and ghosting to establish an optical design that is resistant to strong incidental light sources such as backlight. At the prototyping stage, SIGMA used not only simulations but actual photographic experiments to assess flare and ghosting under multiple criteria, identify the causes of these issues under a wide range of situations, and take measures to mitigate them. In addition, SIGMA’s Super Multi-Layer Coating helps further reduce flare and ghosting and provide sharp, high-contrast images even in backlit conditions.