Another 7D problem...This time Flash

Brocks

Brocks

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From my last question, The same wedding. The couple had a choreographed dance routine for their first dance. It was unannounced and took us all by surprise!

I started using the camera in AV mode with the EX580II in Auto....I got a load like this:

4590287094_436559bc11.jpg


So I switched to Program AE and got some like this

4589667655_c51bb035dc.jpg


What I don't understand, one was done in AV mode. With a wide appature and the external flash on full auto. I hoped that the flash would have shortened the shutter speed.

On the other image I was in AE program. And the flash gave a clear image. Both are f/2.8 and iso 200. What has ae program done that av did not. What determined the shutter speed?
 
Using flash with little available light your options are M and P. Av will try to take an available light shot and add a little fill flash.
P knows you don't want a blurry picture so it adjusts the settings for you. In M you set aperture, ISO and shutter speed so the flash output changes to get the exposure right.

edit. also remember the flash quenches based on reflected light so the exposure will be under when some white/reflective object is in the frame. use flash compensation when this happens.
 
Brocks said:
I hoped that the flash would have shortened the shutter speed.
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Unfortunately this is where your understanding is wrong.

Basically in P, Tv and Av modes the flash works differently. If you read the manual or have a look here you'll see that basically the camera exposes differently. From Page 2 of the link:

The overriding principle of Program (P) mode in flash photography is that the camera tries to set a high shutter speed so that you can hold your camera by hand and not rely on a tripod. If that means the background is dark, so be it.
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Av mode lets you set the depth of field by specifying the lens aperture. The camera then chooses a shutter speed ranging from 30 seconds to the camera’s X-sync speed, in order to expose the background correctly. If that means the shutter speed is some really low value so that you need to use a tripod to avoid camera-shake blur, so be it. In dark conditions, therefore, Av mode works in slow sync mode.
Click to expand...

In this mode [Tv] the camera lets you change the shutter speed. It then automatically chooses an aperture setting to expose the background correctly. Flash duration (flash output) is determined by the flash metering system. In other words, the camera always works in fill flash mode when it’s in Tv mode - it always tries to expose the background adequately, unlike P mode.
Click to expand...

So basically there isn't a lot of difference in the way the flash works in Av and Tv.

This is exactly what you see in your examples.

Image 1 is in Av. It has exposed to get the background right. It is a long exposure so it looks blurred but the foreground detail is highlighted by the flash.

Image 2 in P mode has underexposed the background but given you a usable shutter speed.
 
as a general rule, when indoors on Av mode, the flash works as a fill light. as Freester said, the camera will try to preserve the ambience and expose for the background as well.

when using flash, i'm almost always on M mode. set a reasonable shutter speed and aperture, and let the e-ttl take care of the exposure. if i don't like the exposure, i just use flash exposure compensation to adjust.

and i seriously wish that people will just stop blaming their equipment when their photos don't turn out right.
 
I was caught out with the way Av works when I shot at a wedding with my 30D and 580EX for the first time. The camera operates in slow sync mode when you use Av mode.

Most will recommend that you shoot with manual exposure so that you decide how much ambient light you pull in and then you use bounced flash to top off the shortfall. Typically for such scenes I will shoot at something like 1/60, f/2.8, 1600 ISO and bounce the flash, letting ETTL take care of the flash exposure. I may need to adjust FEC a little to get the balance just right, but it means I can control subject blur and also not have those awful dark backgrounds.

Check out this website for lots of good stuff - http://neilvn.com/tangents/
 
Yes, don't believe what you read about "shutter speed has no effect with flash" - particularly if your subject is not someone sitting still waiting for their photo to be taken.
 
Some more good explanations there thanks everyone

Will, who blamed the equipment? I didn't appreciate how the flash was controlled and asked for an explanation simple as that. How else do I learn?
 
the 7d with all its "new" technologies can be quite unpredictable. i'm sorry if that came across harsh, but that was the first impression i got when i saw the topic. i apologise if that wasn't your intention.
 
I must admit I get lazy with my 580exII. I generally use manual and 1/125th sec, F8 and let the flash sort it out :D
 
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