580 ex not as bright

I've got a 580 ex and it seems to me that somehow the power's diminished over time. Shooting in the same location indoors using ettl, it seems like my shots are coming out under exposed these days. I'm still using the same settings (in manual mode) as I've always done except now it seems like I have to dial it +1/3 fec. Doing this, I feel like the flash power is to much. Not as balanced as it used to be. Is there a problem with my flash or is this plain old user error?

I have personally found ettl shots tend to come out a wee bit underexposed. So I usually brighten a bit in PP or just shoot manual =)

are you sure its not the ettl preflash firing only. Not unheard of defective Canon 580EXII's underexposing.

If you have an EOS body with "Auto Lighting Optimizer" and it is turned on, it can minimize the effect of both AEC and FEC.

Thanks for the replies guys.
@ AlanU, I'm sure it's not the pre-flash firing. I was just comparing shots I had taken in the same location with the same light conditions (all indoors) of a few months ago versus ones that I had taken recently and the recent ones seem to be a bit under exposed versus the ones from a few months ago.

@ CliveyBoy, Unfortunately my 30D does not have ALO.

@ madman, since I'm shooting in a bar and constantly moving around, shooting with the flash on manual is not really an option for me. Unless of course you know of a method to achieve good results in this situation. Would be happy to learn.

Thanks again. Any others?

+1/3 FEC isn't enough for most situations. Use +1 as your default, and adjust your FEC based on the histogram.

Thanks guys. I think I stumbled on the problem last night when I was checking my camera. The body was set to -1 fec ( think I left it there when I was using the built in flash one day) so when my 580 was set to 0 fec it would under expose. Will check it out if this was the problem. Thanks for all the replies. As usual, most problems turn out to be User Error!!! LOL.