questions on speedlighting

noob here.

1) if i were to use two flashes, a 580 and 430 manually ... if i set them at say 1/8 power ... does that mean they are not producing the same amount of light? (one being stronger than the other?)

2) re: ETTL II
2a) with multiple flashes, is there a chance to overexpose the shot, if you had a large number of speedlights all pointed at the same location?
2b) will the flash compensate for brightness if the flash is pointed upwards for bounce?
2c) when both a 580 and 430 are used ETTL, does that mean each of them are firing at different strengths or will they have equal strength (assuming it is within both their capabilities).

1. Yes. The flashs are firing at 1/8 of their max power, so the 58 'at 1/8 will be more powerful then the 430 at 1/8

2. Honestly no clue

If you are using two flashes in ETTL you can set them up as groups with a pre-determined ratio or just mount them together. Given the number of light modifiers out there designed to work with more than one speedlight in them. . . . .

As far as flash compensating for bounce. The flash doesn't car where it's pointed. In ETTL the flash power is determined by reading the illumination of the subject via the cameras meter through the lens. The camera pops the preflash, looks to see what lights up and how much, then makes a determination as to how much more light is needed. Of course that doesn't mean it will be able to give you enough light. . . .

mike cabilangan wrote in post #16656947
1) if i were to use two flashes, a 580 and 430 manually ... if i set them at say 1/8 power ... does that mean they are not producing the same amount of light? (one being stronger than the other?)

Yes

If all flashes are on the same channel and firing group and all use the ETTL protocol (of course), then all of them should fire the preflash then will adjust accordingly.

Yes, the pre-flash will help the flash know how much light it should output to achieve "18% grey" on your point of focus.

Not sure. I've not tried that out. I seldom use ETTL mode when using more than one flash and opt for just using manual mode. I can only recall one instance of using a tandem of flashes in ETTL mode once and I felt that it was just by luck that the shot came together immediately without me having to chimp around with the settings or jump over to manual mode. It was for an outside overcast day shot in the shade and I had a hot shoe cable tethered 580ex II shoot through an umbrella to light the subject and also trigger a 430ex II to act as rim and a bit of background fill.

" .. 2a) with multiple flashes, is there a chance to overexpose the shot, if you had a large number of speedlights all pointed at the same location? .. "

No. (Or at least only if they were so many & so close that all their minimum outputs were not sufficiently low. Under ETTL II they go lower than 1/125th.)

" .. 2b) will the flash compensate for brightness if the flash is pointed upwards for bounce? .. "

Yes, as above.

" .. 2c) when both a 580 and 430 are used ETTL, does that mean each of them are firing at different strengths or will they have equal strength (assuming it is within both their capabilities) .. "

Pre-flashes are timed per Group, there's no pre-flash separation within a single group and also there's only one resultant power fraction command per group. So, say 2 580ExIIs under ETTL II within a single group but at different distances to the subject, will contribute differently (also influenced by zoom & modification). Similarly a 580 & a 430 within a single group but equi-distant will have a different contribution, as per their GN ratio (zoom & modification being equal).

mike cabilangan wrote in post #16656947
noob here.

1) if i were to use two flashes, a 580 and 430 manually ... if i set them at say 1/8 power ... does that mean they are not producing the same amount of light? (one being stronger than the other?)

2) re: ETTL II
2a) with multiple flashes, is there a chance to overexpose the shot, if you had a large number of speedlights all pointed at the same location?
2b) will the flash compensate for brightness if the flash is pointed upwards for bounce?
2c) when both a 580 and 430 are used ETTL, does that mean each of them are firing at different strengths or will they have equal strength (assuming it is within both their capabilities).

If everything is on auto, #2 is a YES, it will automatically compensate for light loss when bouncing. I do that with my T1i and 430 flash all the time.

thank you very much! will digest on these ... to help me decide on my next step on speedlighting.