Another SONY α System: Utilize Mount Adapter(9)

By Junichi Date / CAPA asia

Back-illuminated full-frame image sensor greatly improves light collection effociency and prevents color cast at the peripheral area


Sony α7RII
Voigtländer, Super Wide-Heliar II 15mm, F4.5, F8, 1/400 seconds, ISO 100, WB: Auto

The α7RII is equipped with a Back-illuminated 35mm full-frame CMOS sensor (Exmor R). This sensor is superior in terms of high sensitivity, and capable of receving light incident from oblique angles. The greatest benefit of this capability is seen when using an ultra-wide-angle lens and a rangefinder camera with short back focus.
The flange-back distance of the Leica M-mount is 27.8 mm, so in the case of a Sony E-mount with flange-back distance of 18 mm, it is possible to properly focus at infinity even if a mount adapter is attached. Except for a few special exceptions, ultra-wide-angle lenses with short back focus—in which the back side of the lens protrudes—can be mounted to the α7RII (α7 series) body without the shutter curtain touching the sensor plane.

The Super Wide-Heliar 15mm F4.5 II has an ultra-wide-angle of 15mm, and filter diameter of only 52mm, so a key feature is compactness like the FE35mm F2.8ZA, even when a mount adapter is attached. The rear lens projects out far from the mount surface. This sort of lens with short back focus can be made close to a symmetrical optical system, even with an ultra-wide-angle or wide-angle lens, and this is advantageous for achieving greater compactness without losing optical performance.

■ Cosina VM-E Close Focus Adapter
This mount adapter is for Leica M and Voigtländer VM lenses. It features a helicoid mechanism with a 4mm stroke. Most lenses for rangefinders have a long minimum focus distance, and this helicoid mechanism conveniently allows shortening of that distance. A lock engages at infinity, so there are no worries about the helicoid mechanism coming out.

For more information
cosina / accessory

α7R II with back-illuminated full-frame image sensor

Higher resolution, sensitivity, and readout speed
As the world’s first* 35mm full-frame image sensor with back-illuminated structure, this 42.4-megapixel CMOS sensor enhances light collection efficiency, expands circuitry scale, and, with the help of a quick-transmission copper wiring layer, outputs data about 3.5 times faster**, while minimizing image noise to reveal fine details in every picture.

*Among digital cameras with a full-frame image sensor. As of June 2015 press release, based on Sony research.
**In comparison with the α7R.

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