: like the M series, but with an "A" setting on the aperture ring, thus supporting additionally shutter priority and program operation
: like the M series but, but with an AF motor in the lens
: A-spherical lens, explained below
: like A series, but supporting modern-age auto-focus (AF motor in the camera body) and digital communication with the camera body
: like FA, but the optics are optimized for both film and digital
: like FAJ, but optimized for digital bodies and covering the image circle of the reduced-size digital sensor
DA L (a.k.a 'L' or 'DAL' kit)
: like DA, but featuring a very light construction, thus optimally paired with very compact and light bodies like the K-m (plastic mount, no hood, no quick shift but cheaper than DA)
: further development of the F-series, more extensive communication with the camera body
: like FA lenses but without an aperture ring, thus only operable on bodies that can control the aperture electronically
: the original K-Mount lenses, full 35 mm frame coverage, made out of metal, extremely solid and well constructed, great mechanical feel. Capable of only manual metering and aperture priority
: like the K-series, but generally smaller and lighter
: Supersonic Drive Motor. For Smoother, quieter, faster and facilitates simultaneous use of manual and auto-focusing operation using a built-in supersonic motor equivalent to Canon's in-lens ultrasonic Motor. Pentax calls it as "quick-shift focus system"
: refers to a Super Protect lens coating applied on all Pentax lenses, where the surface is coated with a special fluorine compound to repel dust, water and grease, making it easy to wipe off fingerprints and cosmetics.
: the star sign follows the lens series designation (e.g., A*, FA*), and denotes a high-performance lens that uses special-glass elements.
: a lens that uses one or more a-spherica
l elements (aimed at achieving flat field and corner sharpness with wide-angle lenses).
: a lens that uses extra-low dispersion glass elements (aimed at reducing color aberrations in telephoto lenses).
: is the Pentax-original Dust Removal system, which helps keep the CCD surface dust-free.
Fixed Rear Element Extension (FREE)
: a lens whose last cell i remains fixed during focusing. FREE lenses achieve low field curvature and low spherical aberrations not only when focused close to infinity but also at very short distances. For normal applications the FREE system leads to small physical extensions, and thus allows the design of physically smaller and lighter lenses. For macro applications FREE lenses exhibit non-proportionately long extensions which aid precise focusing. However, to achieve these positive effects, the FREE design causes the lens focal length to decrease as the focus distance decreases. Pentax has listed FREE as a feature only for prime lenses even though there are zooms that also have a fixed rear elements (e.g., SMC-A 70-210/4, SMC-A 28-135/4).
: a lens that uses an internal focusing mechanism (lens groups are being moved with respect to each other instead of the entire optical assembly being moved towards or away from the film plane); IF is typically used for longer lenses with large front elements in order to reduce power requirements for the focusing motor and to make such lenses easier to use with polarizing and graduated filters. IF lenses typically change their focal length slightly during focusing. They get wider as they get focused closer.
: Similar to the * designation in that the lenses are of very high quality, but not meaning that the lens is being produced in limited quantities. Star-lenses are generally large and expensive zooms and Limited lenses are generally compact and expensive primes with not very wide apertures.
: a Weather-Resistant lens that features special seals and is thus resistant to dust and light rain.
Type of lenses
: A normal lens is light in weight and approximates the perspective of the human eye
Wide-to-Telephoto Zoom Lenses
: A wide-to-tele zoom is what you get as a standard "kit
" lens with a consumer-grade digital SLR body. The range goes from moderately wide through normal to moderately telephoto
Wide-angle Zoom Lenses
: let you get close to your subject while still showing a lot of background information
Telephoto Zoom Lenses
: similar to Telephoto Prime Lenses but smaller apertures
Wide-angle Prime Lenses
: let you get close to your subject while still showing a lot of background information. A dramatic wide angle for a small sensor Pentax DSLR is 16mm or shorter
Telephoto Prime Lenses
: offers excellent image quality at long focal lengths due to a large maximum aperture and magnification of the subject, and can be handheld in low-light situations
: let you photograph physically small objects. The longer the focal length of the macro lens, the more space you can put between the camera and the subject
extracted from: http://kmp.bdimitrov.de/
and some extra info by myself