| From: Pat Chaney <[EMAIL PROTECTED]>
| Subject: Re: EOS Can the 500EX be a master yet not flash?
|
| Don Weiss <[EMAIL PROTECTED]> wrote:
|
| >One additional thing to consider. The 550EX, used as a master, has certain
| >capabilities beyond those of the ST-E2 (beyond the obvious one of being a
| >flash unit!) if you are using an EOS-3 or 1V (and perhaps the D30): The 550EX
| >can control a flash group C whereas the ST-E2 cannot. Flash group C is
| >intended for backlighting, etc. were its contribution to overall exposure is
| >not too significant.
| >
| >This is, as far as I can tell, because flash group C does not participate in the
| >pre-flash evaluation of the E-TTL system. It _does_ have its intensity set by
| >the resulting in-camera flash calcuation, plus or minus group C exposure
| >compensation; it's just that it doesn't do a preflash sequence for the camera
| >exposure system to measure and include in the flash exposure calculation.
| >
| >Canon really ought to produce an "ST-E3" that could control group C also.
|
| Any idea why the ST-E2 can only handle two groups? I'd previously
| assumed that the reason the 550EX could support three flash groups was
| because the 550EX itself was one of them, but from what you are saying
| this is not the case.
It is indeed not the case. I have only two speculations on the ST-E2 not handling
group C:
1. The designers of the ST-E2 were not aware of the decision to _have_ a group
C in the wireless E-TTL technology; either because they weren't informed, or
because the ST-E2 design was frozen before the group C decision was made.
2. The marketers didn't want to sell too many ST-E2's -- uh, I mean, they wanted
to sell more 550EX's.
I can't think of any technical reason a Slave Transmitter (contradiction in terms,
that) using the same essential components as the ST-E2 could not be built
to comprehend group C. Maybe take an extra pushbutton on the back, and of
course extra firmware, but that would be about it. If anyone on this list knows
enough wireless E-TTL technology to suggest why it couldn't, I'd like to have a
chat.
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