Canon Flash: What is it's fill flash ratio?

[dwdallam]

Does anyone know what the fill flash ratio of a Canon flash is using ETTL?

I'm not talking about when your flash fires in a dark room, but, rather, when the flash is truly fill flash, such as in daylight or shade, where you could get a properly exposed image w/o any flash--although it would be with harsh shadows or flat, respectively.

The reason I'm asking is that if in ETTL mode, many flashes are neutral, trying to balance ambient light with flash output. This would be an FEC (on the flash) of 0. For some reason I am thinking Canon's ratio in ETTL is something like -1 to -1.5 the ambient light for fill flash.

Thanks much.

[dchew]

I don't know the official number, but before they went to ETTL, I used to dial in -1.33 to -1.5 FEC, depending on the camera/flash combo (when shooting Av, Tv or M).  Since then it has been much less, say -0.5 or sometimes zero.  That leads me to think you are correct, i.e. there is already some level of negative FEC.

Dave

[dwdallam]

I don't know the official number, but before they went to ETTL, I used to dial in -1.33 to -1.5 FEC, depending on the camera/flash combo (when shooting Av, Tv or M).  Since then it has been much less, say -0.5 or sometimes zero.  That leads me to think you are correct, i.e. there is already some level of negative FEC.

Dave

That's been my experience too. You really have to crank the hell out of it to get it to act like key in ETTL mode. It would just be nice to know the number. I don't think I've ever seen it act like a balance at 0 FEC, except when the ambient light is just above the point where it would automatically act as a key like, such as in a bedroom at night with a couple 60 watt bulbs burning. Then it seems balanced or neutral.

[Rhossydd]

The quick answer is it varies with ambient light levels.

From http://photonotes.org/articles/eos-flash/index2.html
"E-TTL flash works in a similar fashion, though apparently flash output will be lowered by as many as 2 stops when ambient lighting is bright. Canon have not, however, divulged their secret E-TTL fill reduction algorithm, so it’s total guesswork exactly how it works. Apparently, though, the algorithm compares the brightness level of each zone both before and after the preflash, in part to compensate for highly reflective areas."

This site tells you everything you ever wanted to know about EOS flash systems.

Hope this helps

Paul

[dwdallam]

The quick answer is it varies with ambient light levels.

From http://photonotes.org/articles/eos-flash/index2.html
"E-TTL flash works in a similar fashion, though apparently flash output will be lowered by as many as 2 stops when ambient lighting is bright. Canon have not, however, divulged their secret E-TTL fill reduction algorithm, so it’s total guesswork exactly how it works. Apparently, though, the algorithm compares the brightness level of each zone both before and after the preflash, in part to compensate for highly reflective areas."

This site tells you everything you ever wanted to know about EOS flash systems.

Hope this helps

Paul

Yep, I think that is what I read a couple years ago. It also coincides with my experimentation, that you could have to crank like hell to get the flash to match ambient light levels, especial in bright situations. It would really be nice for Canon to have a Cn function that sets the ETTL flash to 0, where it would always tr to balance flash and ambient light. Thanks for the link.

[Rhossydd]

It would really be nice for Canon to have a Cn function that sets the ETTL flash to 0, where it would always tr to balance flash and ambient light.

The problem is 'what is balanced' ? There's always going to be a degree of subjectivity on this sort of issue.
Canon's approach of either leave it to our automation, override our automation by stepped amounts or take full manual control makes sense to me.

What can be confusing is understanding the differences between how the different auto exposure modes work with flash. I've spent too much time reading how it all works and puzzling out what's happening when it doesn't work as initially expected, but come to the conclusion that making it any simpler would involve loosing some functionality. It's one feature of the canon system you have to read the manuals and learn.

Paul

[dwdallam]

The problem is 'what is balanced' ? There's always going to be a degree of subjectivity on this sort of issue.
Canon's approach of either leave it to our automation, override our automation by stepped amounts or take full manual control makes sense to me.

What can be confusing is understanding the differences between how the different auto exposure modes work with flash. I've spent too much time reading how it all works and puzzling out what's happening when it doesn't work as initially expected, but come to the conclusion that making it any simpler would involve loosing some functionality. It's one feature of the canon system you have to read the manuals and learn.

Paul

Paul, the problem is that if you're in ETTL and you want to pop more light in bright light with harsh shadows, you can't. That's because Canon ETTL will, in those instances, decrease fill by uop to -2EV. So you run out of EV comp before you get near taking out those nasty shadows. Then you need to move to manual, which in fast paced photography where light is changing all the time, not really practical. Aside from that, it's pretty easy to get the hang of the Canon flash in ETTL just by using your camera in manual and Av modes and watching what it does. After you get used to it, it's pretty easy to adjust on the fly. And the Canon metering system for flash is quite good too. I just don't like running out of EV comp because the flash wants to do a -2EV when in some instances I want it to do a +3EV, which is impossible in ETTL mode.

[Rhossydd]

Doug, your comment exemplifies Canon's difficulties in defining the correct approach to take.
On one hand you're saying that the "Canon metering system for flash is quite good", but then go on to say that you think it can be 5 stops out for your idea of a balanced exposure("the flash wants to do a -2EV when in some instances I want it to do a +3EV"). Your idea of being able to lock the flash ratio wouldn't necessarily help in a 5 stop situation. Being able to increase the amount of compensation might help, but that degree of change would indicate that something is going wrong with the overall system to me.

Having that sort(+5 stops) of compensation dialled in sounds an exceptional requirement to me, and one that could also blow out mid tones and highlights. If that situation did arise it could be just as easily handled by moving to entirely manual control.

Paul

[dwdallam]

Doug, your comment exemplifies Canon's difficulties in defining the correct approach to take.
On one hand you're saying that the "Canon metering system for flash is quite good", but then go on to say that you think it can be 5 stops out for your idea of a balanced exposure("the flash wants to do a -2EV when in some instances I want it to do a +3EV"). Your idea of being able to lock the flash ratio wouldn't necessarily help in a 5 stop situation. Being able to increase the amount of compensation might help, but that degree of change would indicate that something is going wrong with the overall system to me.

Having that sort(+5 stops) of compensation dialled in sounds an exceptional requirement to me, and one that could also blow out mid tones and highlights. If that situation did arise it could be just as easily handled by moving to entirely manual control.

Paul

That would be 5 stops including the flashes' -3 inclination. So if the flash is saying "Hey, it's too bright, so I'll just add a little shot to the fill at -3EV, then I'd have to increase +3 just to get to neutral, then another +2 (perhaps) to balance the ambient light with the fill flash.  You can't do that because you're beyond the +3EV compensation allowed.

[michaelnotar]

i dont trust the flash, i shoot manual expo mode, expose for ambient with a moderate f stop (F5.6-8) so the flash can adequately light the subject and set the flash too TTL -1 to -2 stops, that way the flash is only adding 1/2 to 1/4 stop of light.

i tested my canon flash, it came out with a GN of 80 (580) several stops less than indicated by the manufacture. that could explain why the flash seems to be 2 stops under even when set to zero FEC. the specd GN of 160-220 (F16-22 at 10 ft) vs real GN80 (F8 at 10ft) is 2-3 stops (not sure exactly what the specd GN is but all canon flashes seem to be about those numbers).

[Hank]

i tested my canon flash, it came out with a GN of 80 (580) several stops less than indicated by the manufacture......

That explains a lot to me.  It's my oversight for not testing it myself, but the flash just never lived up to my expectations.  I need and use fill constantly, and as a result I dumped the Canon system completely.