580EX flash as a master - Group C FEC?

Doug_Kerr · #1 03-07-2006, 12:01 PM

When a Speedlite 550EX flash unit is used as a master in a wireless flash setup, with units assigned to groups A, B, and C, and with Ratio ON A:B C so that the three groups are separately controlled, one can set at the master a flash exposure compensation amount for the C unit/group. (This is separate from the "main" FEC setting, which in this case controls the outputs of the A and B units/groups only.) The C FEC setting is the last stop on the trail of settings traversed with the SET button in this configuration. (See p. 68, items 8 and 9, in the 550EX manual.)

The Speedlite 580EX manual makes no mention of this setting item. Further, it pointedly says (bottom of p. 40) that if you need FEC for the C unit, be sure to set it (and the context is such that this almost certainly imples, "on the unit").

Could somebody with a 580EX confirm for me whether there is or is not a "C FEC" setting available at a 580EX used as a wireless master.

Thanks so much

ChuckWestfall · #2 03-07-2006, 12:15 PM

Doug:

The 580EX is consistent with the 550EX in the respect that FEC values for the C group speedlite(s) should be set on the speedlite(s) themselves. When it is configured as a master unit, an FEC value can also be set on the 580EX (or 550EX) for all speedlites in an E-TTL or E-TTL II wireless autoflash configuration. The C group FEC setting is independent from the FEC value selected on the master unit.

Doug_Kerr · #3 03-07-2006, 01:24 PM

Hi, Chuck,

[ QUOTE ]
The 580EX is consistent with the 550EX in the respect that FEC values for the C group speedlite(s) should be set on the speedlite(s) themselves.

[/ QUOTE ]
Why then does the 550EX, as a master with Ratio ON A:B C, include as the last stop on the trail of settings a "C FEC" item? It is described by the 550EX manual as affecting the C unit(s). [We see this at the top of page 67 and on page 68, items 8-10.] And that seems to actually happen, based on some testing here.

Are you saying that, this notwithstanding, an FEC value for a C unit (in a Ratio ON A:B C configuration) would be better made on the C unit itself (assuming it allows that)? (Of course my 420EX does not, but I would rather not go over to where it is anyway!)

[ QUOTE ]
When it is configured as a master unit, an FEC value can also be set on the 580EX (or 550EX) for all speedlites in an E-TTL or E-TTL II wireless autoflash configuration. The C group FEC setting is independent from the FEC value selected on the master unit.

[/ QUOTE ]
Actually, my testing suggests that, in a ratio ON A:B C setup, the "regular" FEC set on the master (for a 550EX, at least) affects the outputs of the A and B unit(s) but not the C unit. (I need to review my test notes to be absolutely sure, but that is what I recorded in my report!)

This of course would make sense, given that the predicate of the system scheme is that the C unit(s) illuminate a different part of the scene from the A and B units. It would be only by accident that we would want to make a uniform change in the exposure of both portions of the scene. So the behavior of the "main" FEC setting in a Ratio ON A:B C situation, as I think I perceive it from my testing, is ideal.

What am I missing here?

Thanks for your help.

Best regards,

Doug

#4 03-07-2006, 02:26 PM

Hi Chuck...

I hope Doug does not mind my trying to reword it.

I think the question is....If you set FEC, on the camera or on the flash, for A:B does it effect the C flash...or will the C flash be completely unchanged. My understanding/impression has been that the 'C' exposure was relative to A:B...if you increased/decreased the FEC on A:B, the exposure of 'C' would also increase/decrease. The FEC for 'C' would allow you to change the exposure of 'C' relative to A:B.

Net...I know FEC for 'C' is not linked to (does not change)A:B, but is the FEC on A:B linked to C's exposure?

Thanks...JOHN

Doug_Kerr · #5 03-07-2006, 02:44 PM

Hi, John,

No, that is not the question.

The question is: "The 550EX has provision for setting a C FEL on the master when operating in the Ratio ON A:B C mode. The 580EX manual mentions no such provision. Is there such a provision on the 580EX?"

The issue you mention about the "main" FEC setting in an A:B C situation is collateral, and of course I'd be glad to have confirmation on that as well.

Best regards,

Doug

ChuckWestfall · #6 03-07-2006, 04:24 PM

Doug:

I misspoke on the first part. It is possible to set the FEC for Group C from the master unit, whether it is a 580EX, 550EX, MT-24EX or MR-14EX. Sorry for the confusion.

On the second statement, the FEC for the entire A:B:C configuration is independent from the FEC for Group C.

Note that the first step of the entire setting process for the master unit is an FEC value. This value will affect all active speedlites in the wireless configuration, including those in Group C if there is a Group C. In addition, it is possible to set an FEC value for the entire wireless configuration from the camera body, provided that the FEC value on the master unit is set to 0 (zero). The rule of thumb is that FEC values set on the Speedlite will override FEC values set on the camera unless the Speedlite's FEC value is set to zero.

Doug_Kerr · #7 03-07-2006, 04:49 PM

Hi, Chuck,

[ QUOTE ]
I misspoke on the first part. It is possible to set the FEC for Group C from the master unit, whether it is a 580EX, 550EX, MT-24EX or MR-14EX. Sorry for the confusion.

[/ QUOTE ]
That's OK. There are plenty of opportunites in this area to get confused.

I'm glad that's so - evidently, Canon just decided not to mention that in the 580EX manual (I note that there seems to have been an attempt to make that manual not so "daunting" as the 550EX manual!) It would have been disappointing had that capability disappeared on the 580EX!

[ QUOTE ]
On the second statement, the FEC for the entire A:B:C configuration is independent from the FEC for Group C.

[/ QUOTE ]
Not surprising.

[ QUOTE ]
Note that the first step of the entire setting process for the master unit is an FEC value. This value will affect all active speedlites in the wireless configuration, including those in Group C if there is a Group C.

[/ QUOTE ]
Again, not surprising. I may have misinterpreted the results of my testing on this particular wrinkle (I was a bit confused that day, all right - there were over 120 test shots taken!).

Thanks again for getting us straightened out on this.

Best regards,

Doug