600EX RT not illuminating subject in ETTL mode

[chawlee]

I was shooting with my 600EXrt with a 6D in ETTL mode with a plus 3 FEC. Suddenly I noted that the flash fired but the image was pitch black (no illumination). Tried it a few times same result. I took out the other 600ex rt and that worked fine.

On reaching home I noted that if the flash is in manual mode i will get a good exposure but in ETTL mode everything is dark even though the flash unit is firing.  In ETTL If I cover the sensor the flash still fires at the same power as if nothing is in  front of the sensor.

I have also tried it on the 7D with the same problem.

[RobertTheFat]

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@chawlee wrote:

I was shooting with my 600EXrt with a 6D in ETTL mode with a plus 3 FEC. Suddenly I noted that the flash fired but the image was pitch black (no illumination). Tried it a few times same result. I took out the other 600ex rt and that worked fine.

On reaching home I noted that if the flash is in manual mode i will get a good exposure but in ETTL mode everything is dark even though the flash unit is firing.  In ETTL If I cover the sensor the flash still fires at the same power as if nothing is in  front of the sensor.

I have also tried it on the 7D with the same problem.

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Does that behavior apply to both flash units, or just the one? If the latter, it suggests that one of the contacts on the flash's "foot" isn't working properly.

[TCampbell · Accepted solution]

Not sure exactly what is happening... however, in E-TTL mode the camera fires a "pre flash" before the exposure flash.  It's part of the metering system.

It meters the scene with no light (preferably on evaluative metering mode).  It then fires the flash (usually at 1/32nd power) with the shutter still closed but in that instant it re-meters the scene again... and it's trying to work out how much of an improvement occurred by using 1/32nd power (as compared to no flash all).  

Based on that result, it decides how much power should be used for the exposure, the camera then opens the shutter and fires the flash at whatever power level was calculated (plus or minus whatever flash expousre compensation you dialed in.)

This all happens so quickly that most people think the flash only fired once.

I think you're likely seeing the pre-flash and no regular flash.

Check the camera settings with that particular flash in the hot shoe.  It's possible to put a flash in a mode where it performs the pre-flash and uses this to communicate with off-camera flashes... but once the shutter opens, the on-camera flash does not fire.

I don't own a 6D, but on my 5D IV there's a menu item labeled "external speedlight control" and that opens up a menu pages with lots of options... one of which reads "flash firing" with a value of either "enable" or "disable".

Seeing flash firing set to "disable" might be a head-scratcher (why not just switch off the flash) but it turns out the option is there for those who want to use the on-camera flash to communicate with off-camera flash... but NOT have the on-camera flash illuminate the shot when the shutter is open.

If your flash is in E-TTL "master" mode then the menus on the flash will change... menu page 2, soft-button #1 will toggle the flash firing enable/disable for THAT FLASH (in other words you can set this on one of your flashes, but not the other... and swapping flashes would have different behavior.)  You can ALSO set the behavior using the in-camera menu.  For many options, you can only use the in-camera menu if the flash isn't over-riding the value (setting the choice on the flash will take priority over setting it in camera.)

I'd have a peek at that menu page to see if the flash isn't set to disable (it's an icon showing a flash emitting light vs. not emitting light.  When set to disabled the red pilot lamp will go out.)

[diverhank]

It does appear that something is wrong with the flash.  The flash you saw was probably the initial flash to measure the exposure (through the lens) but for some reasons, the main flash didn't fire.  Covering the sensor doesn't do anything for ETTL. That sensor is used only for Ext-A and Ext-M mode.

The only thing I can think of is your wide angle diffuser and/or the catch-eye white panel is partially deployed.  Make sure they are either fully extended or retracted.  The flash behaves very weirdly when these are not locked.

[chawlee]

I triggered it off camera with the YN-E3-RT as a off camera flash set to etttl. Same result. The flash it emits is not a pre flash as it is as strong as when the flash is manual. I am now assuming it has to go to Canon for repairs. I think it is an electronic problem and it is not synchronizing. Thanks for your help.

[TCampbell]

I'm not at home (so I don't have my 600EX-RT with me) but I think the center two soft-buttons (on that top row of four soft-buttons just under the LCD display) are labeled as 'reset' buttons... press and hold for a few seconds.

I'll try to remember to double-check when I get home and update this post.  In any case, there is a reset option on the flash and before sending it for service, you may as well give that a shot.

[chawlee]

Just did that. The problem still exists. Thanks

[NivistaKannan]

Try to clear flash setting from camera (External Speedlite control -> Clear flash settings).

I faced similar issue with my Canon 5D Mark III, clearing the flash settings fixed the issue.

[Phototechguy]

Hello, was this resolved? I didn't see the resolution. I have the same problem.