I used a Cobra Auto2 10 (older film camera flash) on my Canon DSLR 5D mark 3 for an experiment. The flash was working fine. Then I put my newer Metz 58 AF-1 and AF-2 flash back on on the camera.

My flash images using the Metz are now underexposed. It's acting like there's no communication between the camera and flash. What could be wrong?

  • You have two different Metz flashes and they're both not working? Were they working before?
    – mattdm
    Jun 4 '16 at 17:36
  • @mattdm - Yes, I should have kept both models in the question (even if I think that if both new models aren't working, the problem comes probably from the switch between the old one and any of the new ones).
    – Olivier
    Jun 4 '16 at 20:30
  • @mattdm Curious why you deleted your answer. Some flashes use more than 250V, so that could still very well be the issue.
    – Michael C
    Jun 4 '16 at 22:22
  • 1
    @MichaelClark Okay, edited and undeleted, since I don't have a better guess
    – mattdm
    Jun 5 '16 at 1:21
  • @romolo When the 58 AF-2 is mounted on the camera and turned on, are the flash menu options available in the camera's menu? Or are they greyed out like when there is no flash attached?
    – Michael C
    Jun 5 '16 at 3:11

The Cobra Auto 210 is reported to have a very high flash trigger voltage. As you can see from Can using an old flash damage a new DSLR?, this is not safe. Earlier Canon DSLRs could only handle 6V — yours should be able to handle up to 250V, but it's possible the Cobra flash exceeded that. (Also, there is some lack of clarity on whether 250V is okay through the hotshoe, or just the P/C connector.) The thread I linked shows a measurement of 234V, which is below the nominal threshold but a little close for comfort.

If that's the case, you've blown out some of the electronics and will need to send the camera for repair.

  • According to the 5D Mark III Instruction Manual, the 250V limit is specifically for the PC terminal. "Do not connect to the camera's PC terminal any flash unit requiring 250V or more." With regard to the hot shoe the manual only says "Do not attach a high voltage flash on the camera's hot shoe."
    – Michael C
    Jun 5 '16 at 3:33
  • 1
    @MichaelClark, Chuck Westfall and Canon tech support have confirmed the 250V limit is for both the hotshoe and the PC connector: photo.net/canon-eos-digital-camera-forum/00Bq8u.
    – inkista
    Jun 5 '16 at 3:37
  • Was the 5D Mark III a current model when Westfall made that statement in 2005?
    – Michael C
    Jun 5 '16 at 3:46
  • Comments I've found other places online suggest that Canon has kept to this with all models since then. But I don't know for sure.
    – mattdm
    Jun 5 '16 at 3:54
  • It's probably the case. But there is still that warning in the owner's manual. Voltage protection adapters are easy to get and relatively cheap. Why take the risk with a $2500 camera that will probably cost $500+ to fix? amazon.com/dp/B00009UU18
    – Michael C
    Jun 5 '16 at 3:58

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