600 EXII-RT intermittent overexposure

[Da5idC]

- exposure is OK for a few shots then suddenly overexposes completely.

My 600 EXII-RT works OK, then for no reason at all it totally overexposed some photos. Last time it happened I was shooting on a 5dmk4, manual mode, ISO 1250, 1/200 at f2.8, evaluative metering, lens Canon 50mm f1.2,  flash 600EX2-RT on E-TTL, no compensation, on second curtain sync. First two OK, next three blown out. Interestingly, on all five the EXIF data shows under flash "Did not fire, compulsory mode" - also on the two that were correctly exposed. (I checked the EXIF on the 5D and the 7D ,and some are fired, and some are did not fire, with no notable difference between them)

This also happens n my 7Dmk 2 though I can't be bothered to go into my backups to find some examples. The only difference I can think of is that the 7D is usually on center weighted metering.

I am hoping for some solutions this time, regards, DC

[deebatman316]

When this happened did the speedlite’s LCD screen say E-TTL or TTL. If the speedlite IS NOT communicating with your camera correctly. The flash will switch back to TTL and the camera doesn’t believe that a flash is mounted. When this happens is the Speedlite Control Menu still operational. The old off the film TTL relied on light reflected off the film. A flash set to TTL on a digital or late film camera will always cause gross overexposure. Older off the film TTL was omitted from later film cameras. They behave the same way as a digital when the flash is set to TTL instead of E-TTL. The last Rebel film camera was E-TTL only.

[Da5idC]

Thanks for the reply - It's on ETTL, but I'll keep my eye on that at my shoot tomorrow and let you know what happens

[deebatman316]

Are you sure its fully slid into the hot shoe. I've had that problem where it wasn't slid into the hot shoe all of the way causing the flash not to fire or overexpose.

[Da5idC]

Yip, it is definitely properly engaged. It was the first thing I checked and I still try whenever it happens. Only thing that helps is to turn the flash off and on

[deebatman316]

What camera are you using the speedlite on please provide the FULL NAME of the camera in question. Please provide example pictures in the forum. Do this mount the speedlite first with both the camera and speedlite off. Turn on the speedlite then turn on the camera and see if it works correctly. Sometimes the speedlite doesn't establish the proper communication when the camera is already powered up. 

[Da5idC]

As I said above it's a 5DMk4, just like yours.

I'll try your tip about turning the flash on first and see how it goes. If it doesn't work, I'll post some pics tomorrow

[deebatman316]

I also own the Speedlite 600EX II-RT and the EOS 5D Mark IV and NEVER has exposure problems. Even with my other old speedlites and newer Speedlite 470EX-AI never have exposure problems. Try this put the camera in Auto mode it puts the camera back to Factory Default. Will it still overexpose or does it correctly expose.