Flash firing slighty before or after photo get taken

[petra_riddell]

Hi there! 

I have had a 750D (Rebel T6i) for a little over a year now and have barely used the flash function. 

Today I tried to use it and it would take the photo and the flash would fire but the photo would be dark- as if the flash went off to early or to late. 

I'm not sure how to fix this, any ideas? 

The flash fires fine-just at the wrong time and everyhting else on the camera works well. 

- i have tried restoring settings to default and still the same problem

Thanks heaps! 

[ScottyP]

The flashes before firing are just the camera trying to meter the shot and trying to assist the autofocus in seeing the scene well enough to focus.  

If if the final image is dark then several things could be happening 

One, the range of onboard flash is short.   If you don’t have a subject 15-20 feet from the camera the light from the flash will fall off over distance and be of no use. 

Two, the flash can’t keep up if you are firing off multiple shots quickly. It needs time to recharge between shots so you may get one or two where flash fired but then some where it didn’t. 

Three, if there is tricky lighting like a bright background the camera meter may not be lighting the scene enough for your subject. Try a stop of positive flash exposure correction. To make the flash throw out more light. Or go for spot metering so your camera meters for just the middle AF point and put that point on the subject. 

Four, check shutter speed and try to shoot at 1/200 or slower. Faster than that the flash cant work in full power normal mode and it has to work in HSS high speed sync. This lowers the flash’s range and power in order to let the flash put out little light bursts fast enough to keep up with the faster shutter. 

Five, if you must shoot faster than 1/200 do at least be sure HSS is enabled or you won’t get flash at all. 

Six, something I haven’t thought of. 

[RobertTheFat]

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@ScottyP wrote:

The flashes before firing are just the camera trying to meter the shot and trying to assist the autofocus in seeing the scene well enough to focus.  

If if the final image is dark then several things could be happening 

One, the range of onboard flash is short.   If you don’t have a subject 15-20 feet from the camera the light from the flash will fall off over distance and be of no use. 

Two, the flash can’t keep up if you are firing off multiple shots quickly. It needs time to recharge between shots so you may get one or two where flash fired but then some where it didn’t. 

Three, if there is tricky lighting like a bright background the camera meter may not be lighting the scene enough for your subject. Try a stop of positive flash exposure correction. To make the flash throw out more light. Or go for spot metering so your camera meters for just the middle AF point and put that point on the subject. 

Four, check shutter speed and try to shoot at 1/200 or slower. Faster than that the flash cant work in full power normal mode and it has to work in HSS high speed sync. This lowers the flash’s range and power in order to let the flash put out little light bursts fast enough to keep up with the faster shutter. 

Five, if you must shoot faster than 1/200 do at least be sure HSS is enabled or you won’t get flash at all. 

Six, something I haven’t thought of. 

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I'm pretty sure Thing Six is that at least some cameras have a setting in which only the pre-flash is fired. That allows you to use the flash as a focusing aid without having it affect the captured image.

And as for Thing Four, I think you'll find that if you set a shutter speed higher than the sync speed with (non-HSS) flash enabled, the camera will override the setting and slow the shutter down to the sync speed. I discovered that the hard way several years ago. I was shooting portraits with an XTi against a very bright background and trying to lower the dynamic range with fill flash. I was using Tv mode and had stupidly set the shutter speed above the sync speed. Had I been thinking clearly, I would have expected the result to be pictures with only part of the frame correctly exposed, but that's not what happened. Instead, the pictures were all taken at the sync speed (1/200, IIRC) with, of course, badly blown-out backgrounds. At least I've never repeated the error.

[TCampbell]

Go into your camera's menu, find "Flash Control" (on some cameras this is "external speedlite control" but I think cameras with on-board flash call it "flash control") and see if "Flash Firing" is set to "Disable". If so, switch it back to "Enable".  

In the "Disabled" mode, you'll SEE the flash fire... but it technically fires before the shutter is open... as a way of trigger off-camera flash.