580 exII flash is weak at 1/1 compared to yongnuo 560 IV

[Nates96]

Hello,

I recently decided to pick up a used canon 580 EX II, and I am having trouble with the power output of the flash. I got the unit from Adorama and I am kind of assuming they have some sort of quality control testing on their units. However, when firing the flash on full power I have noticed that it is MUCH weaker than my $70 yongnuo 560 IV. I have checked that I am using fully charged eneloop batteries on both units, each on the same manual settings (no high speed sync), and each being triggered by yongnuo triggers, and am getting drastically different results.

At powers below 1/8, the two flash's match power quite accurately, but anything above that and the canon just doesnt seem to be able to output anything more. I have attached a picture of both flashes firing at full power with a zoom of 105mm, and at the same distance and height from the wall. The yongnuo 560 IV is on the left of the frame and the canon 580 ex ii is on the right. The exposure is F22 at a shutter speed of 1/200 with an ISO of 100. 

If anyone has any ideas as to how I can resolve this, I would greatly appreciate it! I have done some research and suspect it could be an old tube light, but I am unsure.

Thanks!!

[Nates96]

Thanks for your reply, Diverdank!

Unfortunately it isn't speculations, I have tested the output of just the canon 580 from 1/8th power up to 1/1 power and have found the EXACT same exposure rating on the histogram of the photo. I am returning it to Adorama on grounds of the product being faulty.

Thanks everyone for your ideas!

[diverhank]

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@Nates96 wrote:
Thanks for your reply, Diverdank!

Unfortunately it isn't speculations, I have tested the output of just the canon 580 from 1/8th power up to 1/1 power and have found the EXACT same exposure rating on the histogram of the photo. I am returning it to Adorama on grounds of the product being faulty.

Thanks everyone for your ideas!

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That's OK, Nates69...I was just wondering but I figured from your picture that it was most likely something wrong.  With a flash meter, I can ascertain my wondering, that's all. Good luck.