using the 430 EX II with Canon 6D

[davikokar]

Hallo,

I just got the speedlite 430Ex II and I am trying to use it on my Canon 6D. I would like to use my camera in Av (aperture priority), but when I set the camer in Av it does not take into consideration the Flash. So, for example, let's say I set 8 as aperture and the camera will set 125/s as exposure time. This 125/s is the same if I have the flash mounted or if I don't have it. I would expect that, since I have a flash, the exposure time is smaller. Am I doing something wrong ? Thanks

[TTMartin]

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@davikokar wrote:

Hallo,

I just got the speedlite 430Ex II and I am trying to use it on my Canon 6D. I would like to use my camera in Av (aperture priority), but when I set the camer in Av it does not take into consideration the Flash. So, for example, let's say I set 8 as aperture and the camera will set 125/s as exposure time. This 125/s is the same if I have the flash mounted or if I don't have it. I would expect that, since I have a flash, the exposure time is smaller. Am I doing something wrong ? Thanks

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Canon flashes will normally try to act as a fill flash unless you force them to behave differently.

If you want to force a higher shutter speed and use smaller than a wide open aperture, try shooting in Manual mode.

Also, when using a flash in P, Av or Tv you have two independant exposure compensations you can set one for the camera and one for the flash. 

[TCampbell · Accepted solution]

Correct - it does and this is an intentional feature.  Though it might not seem like it now, as you do more and more flash photography, you'll realize that this is actually quite beneficial.  

Light suffers from a problem called "fall off".  That means if you're in a dimly lit room and you use the flash, the flash will likely illuminate your subject nicely, but it wont illuminate the background due to the "fall off" problem.  This is the "inverse square law"  that applies to light. (See:  http://en.wikipedia.org/wiki/Inverse-square_law )

Here's a video that shows how this works in photography:

It turns out, however, that if you set the camera to expose for the room as if there is no flash, but then use a flash anyway, you get a nicely illuminated subject, and the camera will also collect enough ambient lighting that you'll get a nicely exposed background.

If you don't want that... then don't let the camera apply it's metering settings to the room.  You can certainly shoot in manual... set the shutter speed to something slower than your camera's max flash-sync speed (for your camera I think that might be 1/160th but you should look it up to be sure) and dial the f-stop you prefer.    The flash will STILL use E-TTL (if you enabled it) and it'll set it's power level to illuminate your subject adequately based on whatever manual settings you've dialed in... but it will not take into account what the light meter wants to do about the rest of the room.

If you DO want the camera to set an automatic exposure, it's going to apply the exposure to the "room".  The flash will be set to correctly illuminate your subject.

We sometimes refer to this concept as "dragging the shutter" because you are using a shutter speed which is much longer than it needs to be if you only intended to collect the light from the flash.  The flash fires VERY quickly (it's on for just a few thousandths of a second).  It's faster than that 1/160th (or 1/200th or 1/250th, etc. depending on camera model) speed.  The flash sync speed is based on the amount of time it takes to wait for the shutter "curtain" to slide open, then fire a flash, then wait for the shutter curtain to slide shut.  But the amount of time that the flash was illuminating was actually much much shorter than that flash sync speed.  

In a sense... you're getting "two" lighting scenarios out of just one photograph... a "flash" scenario on your subject... and an "ambient" exposure on your background.