Doug Kerr
Well-known member
Many of you may recall that I was, a couple of years ago, heavily involved in the matter of Canon's introduction of the "image size compensation" feature for flash units on the Speedlite 580EX.
Prior to the introduction of this feature, Speedlite flash units used on compatible EOS cameras would automatically set the "head zoom" position to correspond directly with the reported focal length of the lens. The object was to optimize the beamwidth in the interest of best energy efficiency and greatest maximum "range" of the flash unit.
However, the reckoning was always predicated on the field of view that focal length would give on a full-frame 35-mm film camera or a digital camera of comparable image size (sensor size). Thus, on smaller sensor cameras, owing to their smaller field of view for any given focal length, the beamwidth given by the flash unit was greater than required, failing to take best advantage of the automatic beamwidth control.
The image size compensation feature on the Speedlite 580EX took the camera's image size (as reported by cooperating cameras, namely the EOS 20D and later) in choosing a head zoom position. As a result, the full potential of optimal energy efficiency and reach would be attained on these cameras.
But, as it turned out, there was a flaw in the algorithm used to execute this plan on the 580EX. A complicated situation ensued.
To bring us up to date on the central issue here, Speedlite models 430EX, 580EX after about serial number 200000, and 580EX II do follow an appropriate algorithm, bringing the full flower (more or less) of the new concept into force.
My new tutorial article, "Improved Beamwidth Control in Canon Speedlite Flash Units", available here:
http://doug.kerr.home.att.net/pumpkin/index.htm#SpeedliteBeamwidth
gives extensive background on this matter and details the various events in its history.
Prior to the introduction of this feature, Speedlite flash units used on compatible EOS cameras would automatically set the "head zoom" position to correspond directly with the reported focal length of the lens. The object was to optimize the beamwidth in the interest of best energy efficiency and greatest maximum "range" of the flash unit.
However, the reckoning was always predicated on the field of view that focal length would give on a full-frame 35-mm film camera or a digital camera of comparable image size (sensor size). Thus, on smaller sensor cameras, owing to their smaller field of view for any given focal length, the beamwidth given by the flash unit was greater than required, failing to take best advantage of the automatic beamwidth control.
The image size compensation feature on the Speedlite 580EX took the camera's image size (as reported by cooperating cameras, namely the EOS 20D and later) in choosing a head zoom position. As a result, the full potential of optimal energy efficiency and reach would be attained on these cameras.
But, as it turned out, there was a flaw in the algorithm used to execute this plan on the 580EX. A complicated situation ensued.
To bring us up to date on the central issue here, Speedlite models 430EX, 580EX after about serial number 200000, and 580EX II do follow an appropriate algorithm, bringing the full flower (more or less) of the new concept into force.
My new tutorial article, "Improved Beamwidth Control in Canon Speedlite Flash Units", available here:
http://doug.kerr.home.att.net/pumpkin/index.htm#SpeedliteBeamwidth
gives extensive background on this matter and details the various events in its history.
