Depending on model, the forward and backward compatibility of a particular flash may be highly variable with some being very limited. The user manuals for specific flash models usually include a compatibility matrix for cameras from the same time period. Similarly, camera manuals usually include a compatibliity matrix for flash of the time. Those two references are the best resources for determining compatibility.
The flash resource pages at "The K-mount Page" (hosted by the German Pentaxians group) are excellent as a background resource to help navigate the maze of initials, interfaces, protocols, and capabilities.
KMP | Flash Systems Evolution
KMP | Meanings of the Pentax Flash Names
Protocol Summary
Which protocols are supported are a clue to which features are supported with which cameras. The year of introduction is in parentheses a reference to camera support.
- Analog dedication (1977) uses the "ready" hot shoe contact
- Program dedication (1981) uses the "ready" and "mode" hot shoe contacts
- Analog protocol TTL (1981) uses the "ready" and "mode" hot shoe contacts*
- Digital dedication (1987) uses the "digital" hot shoe contact
- Digital protocol TTL (1987) uses the "digital" hot shoe contact**
- P-TTL protocol (2001) uses the "digital" hot shoe contact
Some flash are broadly compatible to all K-mount cameras and support most of the above protocols (e.g. AF360FGZ/AF540FGZ) and the features supported on the same. Others are more narrowly focused to support a limited range of cameras and features (e.g. AF500FTZ supports digital dedication (partial) and digital protocol TTL to support SF, PZ, and MZ series bodies with little backward and almost no forward compatibility).
As hinted above, the AF360FGZ and AF540FGZ have perhaps the broadest camera support of all Pentax flash. Both fully support my Pentax Super Program for all features found on the 1981 AF280T to the majority of features on current model Pentax and Ricoh cameras. Interestingly, the 1981 AF280's analog program dedication is still respected on my K-3 such that the flash can automatically set sync speed and appropriate aperture for the flash's auto feature and signal flash ready. The current AF360FGZII and AF540FGZII provide excellent focused support for current model cameras and less complete backward support (e.g. no digital or analog protocol TTL or auto-thyristor) for discontinued and vintage cameras.
Steve
* Some confusion exists in regard to OTF TTL Flash metering in that two protocols have been used. The earlier "analog TTL" uses the analog control/dedication protocol supported by the "ready" and "mode" contacts in combination and was initially implemented on the Super Program and LX bodies along with several flash models of the day.
** Analog TTL was superseded the "digital TTL" protocol common to Pentax AF bodies, though several later camera and flash models also support analog TTL in addition for backwards compatibility.