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DPChallenge Forums >> Hardware and Software >> 550EX Flash Questions
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 06/08/2004 02:38:28 AM · #1
I just bought a Canon 550EX flash to work in conjunction with my 420EX. I had a few objectives with this purchase.

1. I wanted to be able to have two flashes firing for the same photo (working fine, no problems)

2. I wanted to be able to fire the 420 off cam using the 550 (without firing the 550... working fine, no problem)

Questions:

When I setup the 550ex to fire the 420 and not fire itself, the 550 still fires the e-ttl pre-flash for metering. I'm curious as to why it does this. It doesn't make sense to me that the 550 fires the pre-flash since it's not going to fire on the photo. It seems like the 420 (off cam flash) would fire the metering flash instead. Any thoughts?

06/08/2004 07:50:03 AM · #2
Originally posted by jmsetzler:
When I setup the 550ex to fire the 420 and not fire itself, the 550 still fires the e-ttl pre-flash for metering.

The 550EX communicates with the slaves via flashes of visible light from the main tube. This is one of the reasons the 550EX has greater range and horizontal/vertical coverage than the compact ST-E2 Speedlite Transmitter (which also uses a flash tube, but has a visible light filter so that only the infrared portion of the light leaves the ST-E2). So you aren't seeing an E-TTL "pre-flash", but rather the "command signals" being sent by the 550EX.

That being said, I like using the ST-E2 on my camera (at least indoors) because it is a lot less bulky and it frees up the 550EX to be a slave. =]

Message edited by author 2004-06-08 08:06:30.
 06/08/2004 02:38:56 PM · #3
Eddy,

Thanks for that info. It's obviously not included in the manual :)

I am considering purchasing the st-e2 also but I haven't made up my mind yet. The 550 will become my primary flash at this point though and the 420 will be used only for 'slave' work.
 06/08/2004 04:51:28 PM · #4
Originally posted by jmsetzler:
the 420 will be used only for 'slave' work.


Ohhhhh You mean old slave driver!!!!

LOL
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