AA battery pack on the end of the adapter cord that slips into the flash’s battery compartment.
Recycle times are similar to fresh NiCads but last longer.
High voltage battery packs
like the Quantum Turbo also work with the 540EZ via the high power
port on the left side, just above the foot. These will do full power recycles of the 540EZ in about 1.5
seconds.
Canon offers external battery packs for the 540EZ as well, but few people use them because third
party manufacturers offer reliable solutions with more power and features for the money.
Be careful not to do too many flashes too quickly, as this will overheat the flash unit and it may
self-destruct.
Power Ratings
My tests with my reasonably accurate flash meter show my 540EZ to have an actual 100 ISO
guide
number
of 95 feet at the 28mm zoom setting which is about the same as the 97 feet that Canon
reports. But at the 105mm zoom setting Canon reports 180 feet and I only found 140. However the
540EZ is more accurately advertised than most of the other flash units I have tested. They all seem
to be over rated. I suppose they test them in optimal conditions, like long, narrow, gloss white
hallways. I test in a medium sized room with furniture and pictures on the walls.
Summary
The 540EZ is a good shoe mount flash unit with many features and plenty of power. The only
things it seems to lack is the ability to do E-TTL metering with Canon’s newer designed cameras.
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EOS Documentation - 540EZ Operator's Manual
