William Robb replied to my remark: > > I guess the bottom line is that "dedicated" by itself is > > an empty phrase. > > "dedicated" is not an absolute notion, but a relative one. > > it is relative to a (family) of camera body(s). > > > > "Dedicated" is an absolute term, and means that the flash will > communicate with the camera body to set the shutter speed and > aperture (in the case of programmed exposure cameras). > This is by no means an empty phrase, though you probably would > have needed to be around the camera industry 25 or so years ago > to know what the original meaning was. [...]
Thanks for reminding me. I recall the original meaning. 25 years or so ago I got my first slr (pentax me) and though I never possesed or used a pentax flash I tried to stay informed about new pentax stuff through the product brochures available at the photo shops - which included mention of dedicated features. Your (off the top of your hat?) categorization triggered a search for more detailed information, which I found in Dimitrovs pages. In particular at <http://kmp.bdimitrov.de/technology/hot-shoe/> "Flash Systems Evolution, Features and Operation". The categorization there is a bit more refined, and includes a specific category that resembles the Nikon example given earlier in this thread. Moreover it provides details about the evolution of the flash protocol, which I found quite informative. I'll spare you the details, but I'll include the categorization, with some info about what actually is (seems to be) exchanged in the flash protocol. manual flash - camera triggers flash to fire, using trigger contact dedicated flash - flash has additional 'ready' contact via which it tells camera it is fully charged. in response camera switches to X-sync speed, and lights flash symbold in viewfinder (if available). (also switches to some pre-programmed aperture?) auto flash - flash measures output and stops flash output to obtain accurate exposure, provided user selected right aperture on camera program flash - flash has additional 'mode' contact via which it tells the camera the 'brightness' it can output, which the camera, knowing (film) sensitivity, uses to set appropriate aperture. web page mentions 4 brightness levels + corresponding signal at 'mode' contact, measured from AF200T and AF080C. ttl flash - camera is able to tell flash when to stop output, by holding 'mode' contact low (0V) until sufficient light has reached the film plane. it is suggested that TTL sensor is always active, and "stop output" is sent to flash independent of mode that the flash is in, or even regardless of flash being attached to hot-shoe. digital control flash - flash has additional 'digital' contact over which a digital protocol is used to communicate things like aperture, focal length, AF activation, begin of travel of 2nd curtain, iso, maybe also subject distance etc. contrast control flash - uses multiple (2?) flashes, one as main light source, other as fill in, to weaken hard shadows that may result from single flash. this mode requires that body measures both flashes separately. therefore flashes are fired one after the other, which forces ca 50% lower X-sync speeed high-speed flash - shutter is never full open; flash fires multiple bursts of light throughout curtains movevement such that all parts of film plane receive equal amounts of light it seems the metz sca 300 stuff does dedication upto/including ttl flash, and for AF spot-beam enabled adapters even 'grabs' AF activation info to enable the focus assist light. the metz sca 3000 stuff also passes more digital control info. my sca 372 adapter has 'ready' and 'mode' contacts, and does the dedicated, auto and ttl things. it does not pass brightness info, it seems, i.e. with flash in auto mode camera does switch to X-sync speed, but also to same (programmed) aperture. my sca 374/2 AF adapter has 'ready', 'mode' and 'digital' contacts. in addition to the things done by the 372 it lights AF assist, and allows 2nd curtain sync. same thing about auto flash. the sca 3701 does pass more info as is shown on the flash display (aperture, iso, focal length, AF activation). moreover it supports contrast control flash mode. same thing about auto flash (no brightness passed from flash to camera when flash in auto mode). > A "manual" flash is a single output unit which only communicates > output triggering with the camera. > An "auto" flash is a variable output unit which only communicates > output triggering with the camera. > A "dedicated" flash communicates shutter speed and aperture setting > information with the camera, and causes the camera to set the shutter > speed to X-sync and sets the aperture to match the flash output range. > A "TTL" flash communicates flash output with the camera for the > purpose of regulating output. > A "dedicated TTL" flash communicates shutter speed and aperture > setting information with the camera to set the shutter speed to > X-sync and sets the aperture to match the flash output range and > communicates flash output with the camera for the purpose of > regulating output. > Recently, as cameras have thunderbirded, and morphed into lens based > computer systems, the method of communication had changed, but the > principles haven't changed all that much. > > Now you know. > > William Robb thanks again. both your information and the web search triggered by it proved quite informative. Axel. - tried to send a variant of this message yesterday, but it never appeared in my mailbox, nor did I see it in the pdml archive at <http://www.mail-archive.com/[email protected]/> -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
