Originally posted by Lord Lucan But our own reviewers don't agree that the TTL works at all
This is because no matter how many times you say that 1980s-era TTL and p-TTL are completely different technologies, people still confuse them. Pentax DSLRs later than the ist-DS simply do not support the older TTL method to tell the flash when to shut off. So the flash fires at full power, and the camera does whatever it does, and auto-exposure and auto-ISO introduce so many variables that it might
appear to work.
I am not where I can get to my collection of Vivitar flashes, but I think I recall something like seven pins on the bottom of the M/P/O models. As Alex645 says, each brand had their own dedicated pin locations, and the Vivitar 550FD addressed this by having ALL of the pins for all of the supported brands. If Vivitar could have stuffed the pins for Canon, Nikon, and Ricoh in there without conflict, they would have made only one version of the flash, instead of two (M/P/O and C/N/R).
Edit: There are three versions of the 550FD - M/P/O, C/R, and N. Some of the other, non-TTL Vivitar flashes of the period only had M/P/O and C/N/R versions.
Originally posted by Lord Lucan The question remains, does a Minolta or Olympus dedicated flash of the film era have the same electronic interface to the camera that a Pentax dedicated flash has? I
The answer is NO. Because each brand has their own "Flash Ready" pin, and that is the ONLY interface from the flash to the camera, a dedicated Minolta or Olympus flash is not going to send a ready signal to a Pentax. However, if the flash has a self-contained auto-mode, where the flash (not, Not,
NOT the camera!) determines how much light it sees and shuts off automatically, then the center/FIRE pin on the hotshoe may be sufficient. You would have to ensure that the flash is ready before attempting to take a shot. That said, I have no idea if a dedicated Minolta or Olympus (or Canon or Nikon, for that matter) flash from this era would put signals on any other pins that might confuse a modern Pentax DSLR. The usual warnings about trigger voltages apply - I have never had problems with the 550FD/2800-D family, but the 2800 (different from 2800-D) is notorious for high trigger voltages.
But I will say it again: with this style of "dedicated" "automatic" flash, the flash is NOT changing the settings on the camera. You can move the sliders on the back of the 550FD until your fingers bleed, but the flash does not communicate anything to the camera other than "ready" - and how the camera reacts to that "ready" signal depends on the camera. The sliders on the flash are just a table of settings for you to manually change on the camera to get a usable exposure. The flash then provides what it thinks is the appropriate amount of light.