Ken Lin wrote (edited):
I have both, so here are some 580 advantages off the top of my head:
- slightly more power
- slightly slimmer size (same height and thickness, but 10% slimmer in
width)
- easier user interface with dial controls rather than +/- pushbuttons
- 1/3 f-stop increment control possible
- single button to allow both tilt and swivel (550 has separate buttons
for tilt and swivel)
- 180 swivel both directions (550 only allows 90 degree to the right)
About the only marginal advantage the 550 "might" have is when I used
the 550 and 580 with an ST-E2 IR controller, it seems the 580 was just a
hint less sensitive to the control signals beamed out from the ST-E2,
but this could easily be how the signal is bounced around in this fairly
large set, the flashes were placed a bit behind my and each flash was
good 10 feet either side of me, I eventually solved the problem by
rotating the sensor head of the flash to the ST-E2 but swivel the head
towards the reflector umbrella.
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Add to these:
580EX recognizes camera sensor size and will shift the zoom
according.
Example, on a 20D a 50mm with 1.6x focal factor is an
80mm, the 580EX will zoom to 75 or so to compensate.
580EX has 14 custom functions compared to 6 for the 550EX.
580EX is also slightly lighter and slightly more powerful GN at
the tele end.
580EDX is 25% fast
580EX has flash coverage as wide as 14mm compared to 17mm on the
550EX.
580EX has 25 manual power settings; 550EX has 8.
Peter K
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