550EX vs 580EX - output power

Hello,
I know is a little difference between Canon 550 EX and Canon 580 EX, regarding power output. 580EX is slightly powerful than 550EX. But in my case, i think the difference between the 2 flashes is too strong.
I put the flashes in Manual Mode, bounced straight to the ceiling, at 1/128 power, and my camera (Canon 5D with 24-70L) at 400 ISO, 1/200s, f/5.6.
First pic (photo01) is take with OCF 580EX (triggered via Cactus V5s) at 1/128 power, and seems to be ok, regarding exposure.
The next pic (photo02) is take with OCF 550EX at the same settings, and the same position. It's a big difference between the two pics, the second is way too dark.
Photo03 is take with OCF 550EX at 1/1 power output. Is still too dark, compared to first pic (580EX at 1/128).
Then i use my Sekonic L358 lightmeter, to measure the output of the 2 flashes. I set (in the lightmeter) 400 ISO, 1/125s, and the results was:
- 580EX, 1/1 power: f 8.0
- 550EX, 1/1 power: f 4.0
What do you think? Is my 550EX broken? 2 stops difference between flashes? It is normal?
Thanks in advance!

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photo03

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You have a light meter so why not measure based on the GN of the flash.

The 550EX and 580EX have virtually identical power. Your flash, settings, or hotshoe are faulty.

I would agree....something is not working correctly here. They shouldn't be that far apart.

That pic is disturbing btw

Osa713 wrote in post #13461324
That pic is disturbing btw

My wife walked in and said what you looking at.

Osa713 wrote in post #13461324
That pic is disturbing btw

lol, you're right

but no intention

bobbyz wrote in post #13462186
My wife walked in and said what you looking at.

lmao!

It's also possible that the 580 is broken, and is only firing at full power. Why not test both at 1/1 and 1/128.

The 580EX is ok, it just back from service (lamp replace). I have tested the 580EX at 1/128, 1/64, ..., 1/1. It firing ok, the difference of power output is clearly visible.

Thanks everybody for your advices.

I have another question now: it is worth to repair the 550EX, or buy a new (or almost new) 430EX(II) at the same price? I use 580EX for on camera flash (ETTL) and want something for backup (ETTL)
For off camera flash (manual only) i'll buy four units of YongNuo 560. So, for ETTL backup, at the same price: new (for me) 430EX(II), or 550EX repair?

550EX is a bit old and clunky, but they're a workhorse. They take a power pack to speed recharges, and they're twice as bright as a 430EX.