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Old Jan 18, 2005, 12:25 PM   #1
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In using the D-Debel, 550 EX Speedlite and one or two optical slave flashes, I am experiencing some unexpected results at times. Trying to troubleshoot these issueswith the Canon-supplied information, minimal as it is,has proven to bea real challenge:sad:. I have found this page to be very helpful in filling in the gaps:

http://photonotes.org/articles/eos-flash/

Does anyone know whether the D-Rebel/550 EXcombinationconforms tothe older ETTL metering system or the newer ETTL II system?
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Old Jan 18, 2005, 1:20 PM   #2
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E-TTL
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Old Jan 20, 2005, 7:04 AM   #3
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Thanks.

For those who might have similar difficulties, here is my hard won analysis of the problem:

When using the Canon 550EX flash with the D-rebel and optical slaves we experienced inconsistent exposure. Sometimes the slaves added light, sometimes their use actually reduced the light available and still other times they had no effect whatsoever. It turns out that when using the Canon ETTL dedicated flash function, the 550Ex puts out a brief pulse of light (which the camera uses for metering) followed by the main pulse used to make the photo. The time between these pulses is so short that it is not obvious to the naked eye.

Sometimes this metering pulse triggered some or all of the slaves, which, of course, could not re-charge fast enough to fire again when the main pulse came along mere milliseconds later. The slaves did, however, add light to the metering process, which could (sometimes)cause the camera to direct the 550EX to lower its output. Because the metering pulse is generally at much lower power than the main firing of the 550EX, occasionally the slaves would fail to trigger until the main pulse came along and in these cases everything seemed to work as expected.

Very little of the info required to figure this out was in the Canon supplied documentation.
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Old Jan 21, 2005, 4:47 PM   #4
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cjny wrote:
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When using the Canon 550EX flash with the D-rebel and optical slaves...

Sometimes this metering pulse triggered some or all of the slaves, which, of course, could not re-charge fast enough to fire again when the main pulse came along mere milliseconds later. The slaves did, however, add light to the metering process...
This system is really 'not' designed for optical slaves...
It's a Master/Slaves relationship with clear timing and control -> In a Canon system, all Slaves including the Master fire at once in the final burst (ie the 'multiple' pre-flashes are only used for measurements):




If you really use the wireless E-TTL correctly, it's quite flexible and allow (1)ratio, (2)flash exposure compensation and (3)flash bracketing right from the Master unit (where the photographer is) without even touching the slave(s)!
http://eosseries.ifrance.com/eosseries/en/flashwork/
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Old Jan 25, 2005, 6:49 PM   #5
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Of course, all of that is correct (except that the wireless system has a rather limited range).

The real problem, though, is that underfunded state agencies cannot afford to replace all their old equipment just because a manufacturer decides to update their design and thereby obsolete their older stuff.

So, we are forced to try to "get by" with fully functional, really great gear whose only flaw is that it was manufactured a few years ago. I understand why it happens, but it would be easier to take if Canon AT LEAST supplied sufficient information that one could figure out how the system really works.

Another example: We have a 480 EG Speedlite - great flash, rather expensive, but not compatible with the D-Rebel. :sad: And it's not just the TTL functionality that won't work, the Rebel won't even fire the thing in manual. I could go on and on but I've already exceeded my quota.

Thanks, again, for the input.

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Old Jan 25, 2005, 8:26 PM   #6
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Isn't "frustration the mother of innovation" or something like that? It sounds to me like you have made good progress despite the available tools and information.

I'd take up the old flash incompatibility problem as a challenge, to see if some combination of cheap devices might make it work. I think it should... At least an optical slave.. I'd also try to manually meter the various flashes and shoot with them that way. Actually, with a DSLR, you can even get by without a meter -- the histogram's your meter. But, I don't know what you're shooting and how dynamic it is..

Here's some more info on EOS flash systems:

http://photonotes.org/articles/eos-flash/

http://photography-on-the.net/forum/...ad.php?t=46311
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Old Jan 26, 2005, 8:45 PM   #7
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cjny wrote:
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Another example: We have a 480 EG Speedlite - great flash, rather expensive, but not compatible with the D-Rebel. :sad: And it's not just the TTL functionality that won't work, the Rebel won't even fire the thing in manual.
You might want to give this a try: http://www.bhphotovideo.com/c/produc...l_Adapter.html


ie bypass the Canon's old TTL cord and use the regular PC-sync cable instead... It's an ISO hotshoe after all!
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Old Jan 29, 2005, 4:11 PM   #8
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A hot shoe /pc adapter was the first thing we tried in order to save the venerable 480 EG. Unfortunately, it doesn't work for some reason. While we can trigger other flashes this way, the 480 refuses to fire. Perhaps the flash is faulty (although it works fine with our old EOS 3 film camera).
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