Here's a summary of what we've finally concluded about TTL support on Pentax DSLRs:
- Pentax *ist D: Full TTL support for the internal flash and any external TTL flash used with any lens
- Pentax *ist DS/DS2: TTL support for external TTL flashes only (Must be in M mode for manual lenses or when away from "A." Extremely fast apertures cannot be used)
- Pentax *ist DL/DL2: No TTL support
- Pentax K100D/K110D/K10D: No TTL support
Sadly, since the DS/DS2's both have the TTL sensor, TTL support for the built-in flash must be disabled via firmware. Also, if P-TTL is available on the external flash, it will be used over TTL.
More clarification for DS/DS2 users:
-TTL features are identical in both models
-To obtain TTL with M, K, or M42 lenses (or when using extension tubes), the mode dial
must be set to M.
-The built-in flash only supports P-TTL and therefore cannot be used with M, K, or M42 lenses.
Quick Definitions:
-TTL uses a real-time sensor to control lighting during exposure. This sensor is only avaiable in the *ist D, DS, and DS2 DSLRs.
-P-TTL calculates lighting before exposure using a preflash shot and does not function if the aperture value is unknown.