I've been using my 580EX II for years with no problems but now it refuses to work correctly and I think that it needs to be sent to Canon for repair but first I thought I would ask for an opinion to forum members.
I always use the flash as fill in HSS for bird photography and normally I'm dialing in at least -1 FEC, using Av mode.
A few months ago it happened a few times that the flash would switch automatically to TTL and fire at full power for some time. No matter what I did I was unable to stop this behaviour until the flash decided to behave again without any intervention on my part.
Now the flash is not respecting the FEC that I dial in, I can fire a burst and every sinlge photo will have different amounts of flash light. Sometimes the flash seems to fire at full power and after that the next shot is severely underexposed because the flash doesn't fire. Another thing that happens and I don't fully understand is that sometimes the metadata says that the flash fired, but when looking at the photo it actually didn't.
I've tried switching camera bodies and the results are the same.
I'm attaching a couple of pictures I took of some tree bark out of my window with -1 stop FEC, better beamer and flash mounted on camera with external battery pack attached. You can see the difference in flash output. After these two shots, the flash didn't fire in the third and fourth photos of the burst, which are almost completely dark.
Please let me know if this looks like a flash failure or user error, I haven't been able to figure out any way to solve this.
Thanks in advance for your help.