perhaps this explanation found below the linked chart might be of assistance to some readers
Pentax K-Mount Lens Series Explained: The differences between various Pentax lens series
In a nutshell
There are several series of Pentax K-mount lenses; the ones currently being produced include the DA (digital), DA L (cheap digital kit), D FA (full-frame, digital optimized), and FA (full-frame) series. While all Pentax K-mount lenses ever produced are compatible with all current Pentax DSLRs (in some cases with restrictions in that not all exposure modes of the camera are supported by old lenses), there are significant differences between each lens series and each has different features. Furthermore some of the newer lenses do not work with older cameras. We'll be exploring the differences between the various K-mount series lenses in this article: . . .
smc PENTAX-FA
The second generation of autofocus lenses
Sub-groups: FA* (professional) and FA Limited (compact high-end) series
Image format covered: 24 x 36 mm
Suitable for APS-C digital sensor format and 24 x 36 mm "full frame" format
Autofocus with screw drive system
Aperture ring
Automatic aperture setting is available*
Certain zoom lenses feature the power zoom function**
In production: Only five of the original 42 lenses are still in production (as of May 2010: FA 35, FA 50, FA 30/43/77 limited)
The FA series lenses are autofocus and allow for
certain modern cameras (film and digital) to automatically set aperture (Tv mode), shutter speed (Av mode), or both (Program mode). You can also set exposure manually if the camera body allows for this. On recent camera bodies (e.g. *ist and all digital SLR cameras) you use dials on the camera body to set the aperture value (the aperture ring on the lens must be in the "A" position at all times). On older models (such as ZX-5N, MZ-5N, LX, ME, MX, K1000) the aperture is set with the aperture ring on the lens.
Three FA "Limited" lenses were made available in 2001. Except for these and the 35mm f/2 and 50mm f/1.4, the FA series, which consisted of 42 lenses total, has been discontinued.
While FA lenses are identical in operation to F lenses, they feature improved electronics that support the MTF program line.
The FA series also includes 11 "star" lenses (FA*) that employ the finest of Pentax optical and mechanical engineering.
*Exceptions: The smc PENTAX-FA Soft 85mm F2.8 and smc PENTAX-FA Soft 28mm F2.8 lenses have no "A" setting on the aperture ring. Hence they work like smc PENTAX-M lenses with respect to exposure; they are still autofocus. The "A" setting has been removed because the degree of image softness is controlled by the aperture ring and it would be meaningless to let the camera decide the setting.
**Power zoom is only supported by certain camera bodies. The following lenses feature power zoom:
-SMC Pentax-FA 28-80mm F3.5-4.7
-smc PENTAX-FA 28-105mm F4-5.6
-smc PENTAX-FA 70-200mm F4-5.6
-smc PENTAX-FA 100-300mm F4.5-5.6
-smc PENTAX-FA* 28-70mm F2.8 AL
-smc PENTAX-FA* 80-200mm F2.8 ED [IF]
-smc PENTAX-FA* 250-600mm F5.6 ED [IF]
. . .
smc PENTAX-A
The third generation of manual focus lenses
Sub-categehory: A*
Image format covered: 24 x 36 mm
Suitable for APS-C digital sensor format and 24 x 36 mm "full frame" format
Automatic aperture setting is available
In production: No
Remarks: smc PENTAX-A lenses are manual focus.
Regarding exposure control they work like FA lenses.
The A series also includes 9 "star" lenses (A*) that exemplify the finest in Pentax optical and engineering.
smc PENTAX-M
The second generation of manual focus lenses (generally smaller than K lenses)
Sub-categhory: M*
Image format covered: 24 x 36 mm
Suitable for APS-C digital sensor format and 24 x 36 mm "full frame" format
Manual aperture
In production: No
Remarks: smc PENTAX-M and smc PENTAX (commonly know as "K") lenses are manual focus and have no "A" setting on the aperture ring. These lenses allow for the camera to automatically set shutter speed (if it has the Av auto-exposure mode). You can also set exposure manually if the camera body allows for this. The ZX-5N is an example of a body which provides Av mode as well as manual exposure mode with M and K lenses. Almost all K and M lenses have an automatic diaphragm.
Some recent bodies cannot use M and K lenses or only with some limitations. An example are the *ist D and K (digital) series. In M mode you set the aperture using the aperture ring on the lens; the camera will set the shutter speed when you press the green button (or AE-L button if the camera has no green button). Or you can set the shutter speed manually (there is no exposure read out in the finder to assist you).
The M series includes a single "star" lens (M*) that exemplies the finest in Pentax optical engineering. That is the smc PENTAX-M* 300mm F4.
Pentax K-Mount Lenses Explained: The differences between various Pentax lens series