Pentax, the Japanese camera and lens maker, introduced the electronic aperture control system for its cameras with the launch of the Pentax KA-mount system in 1983, and the SMC Pentax-A 28mm f/2.8 in 1984, after an earlier shift from the M42 screw-mount Takumar lenses to the SMC K-bayonet mount in 1971. The KA mount, also known as the 'PK-mount,' maintains the manual focus feature of the original lens design while adding full aperture- and shutter-priority, program, and manual exposure modes on compatible cameras.
The mount system, featured on the Pentax Super A (known as the Super Program in the USA), incorporates electronic contacts on the K-mount flange that allow the camera to control the aperture from the lens when the ring is set to 'A' and to read the focal length for in-body shake reduction features.
Interpreted in terms of camera capabilities, all KA-mount SLR/DSLR cameras, manufactured from 1983 onward, can use SMC Pentax-A lenses in all exposure modes, including manual focus mode. This mode remains available when the lens is set away from the 'A' button position to one of its aperture settings.
Designed for full-frame K-mount film cameras, the SMC Pentax-A 28mm f/2.8 is a compact, all-metal wide-angle prime recognized for its robust build, pleasing color rendition, and strong center sharpness. A favorite with film shooters and digital adaptors, the lens is a 7-element in 7 groups construction, with 5 aperture blades.
The lens measures approximately 57 mm in diameter × 42 mm in length, weighs 170 grams, and accepts 49mm filters. It shares the same optical formula as the second version of the Pentax-M 28mm f/2.8 but adds an 'A' setting on the aperture ring, enabling full program and shutter-priority automation on compatible Pentax bodies.
On the 10MP CCD Pentax K-m (K2000 in the US), introduced by Pentax in 2008, the lens is equivalent to a 40mm prime (42mm to be exact) on a 35mm full-frame camera. The focal length is still considered to be within the standard normal range, capable of capturing images that mimic what the eye sees, in natural perspective. The lens sits between the wider 35mm and the standard 50mm, a versatile choice for various photography genres, including street and portrait photography, city and urban scenes, as well as documentaries and photo journalism.
The Pentax K-m is a compact entry-level digital SLR camera fitted with a Pentax KAF2 lens mount, which adds auto-focus features to the lens mount system. The camera, well vetted for its capabilities and CCD image captures, makes for a very compact and highly recommended digital SLR camera with a legacy lens setup for CCD image enthusiasts.
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