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Jason
12-27-2013, 09:08 PM
I've been using a Canon 420 EX Speedlight on my 5DmkII with absolutely no problem for the last three years. Over the last few months, I've noticed that anytime I use it my images are horribly underexposed. One of the things that I realized is that it seems to be firing early. I was suspicious of this because I seemed to be seeing the flash as I was looking through the viewfinder--I hadn't noticed this before, and I would think that normally the mirror would go up and you wouldn't see the burst of light. I think I confirmed this was the problem by taking a shot of myself in the mirror. No flash showed up in the image, once more leading me to believe it is firing too early. I also put the flash on my old Rebel XTI and got the same result, so I'm fairly certain the issue is not with the camera.

I've cleaned the contacts not flash and that didn't help. The 420ex does not have any manual controls, so I'm really at a loss. Playing with the flash exposure compensation did nothing, further making me think it's a timing issue. Has anyone else run into a problem like this? Maybe it's time to retire the old 420ex...

ericmark
12-27-2013, 10:49 PM
I had a similar problem and it turned out to be red eye correction on the camera where it is suppose to give a very short flash before the main one. However it was camera not flash at fault and looking at it unless the camera gives out some sort of signal how would the flash go early. Late yes it could do that but not early. Has to be a camera setting. I use Pentax not Canon so can't give exact answer but the other thing with Pentax is leading and trailing flash. It can be set to fire either when both focal plains are just fully open or just before it starts to close. In the main for long exposures and if you take picture of a car passing with lights on one will extend the head lights the other will extend the tail lights.

My big problem was trying to trigger second flash with flash on camera. With built in every time the pre flash set off slave before shutter opened and no way could I find a way around the problem but using a hot shoe flash slave worked A1.

My Vivitar flash gun uses AA batteries and I have found with 2500mAh the re-charge time is quite short but use some 700mAh and it takes an age to recharge the capacitors ready for next flash with that in mind it is possible the Speedlight has always given a pre-flash but batteries were good enough to recharge capacitors for main discharge but as batteries age they can no longer recharge it in time.

However if it's flashing too soon fault must be in camera in the main hot shoe flash guns don't give a pre-flash only the cameras built in flash gun normally does that.

Jason
12-28-2013, 01:44 AM
Thanks, ericmark. Glad to hear I'm not the only one that has run into this.