Canon 5D and Flash DOF help

[joe_bailey2]

I am using a Canon 5D with a Canon EF 24-70L lens and a 550EX

flash. I am taking indoor photos with average room lighting at a

distance of 4-8 feet. The camera/flash default to a shutter speed

of 60 and f-stops between 2.8 and 4. This is giving me a very

narrow depth of field. I need some advice on how to increase my

depth of field. Do I compensate with the AEB and if so, does my

flash automatically adjust for the smaller aperture? What is the

best ISO setting to use in this situation? Thanks....

[steve_dunn2]

<p>You're shooting in P mode. If you want control over DOF, you want to be in M, where you can choose your shutter speed and aperture freely. The flash will automatically fill in however much light is needed (as determined by the flash metering system, which isn't always right on) to bring the subject up to a normal exposure. Alternatively, you can use Av, with the CF which locks the camera's shutter speed at its maximum X-sync speed, but that is not likely to be the best choice.</p>

 

<p>The best ISO depends on what you want. You want the lowest ISO possible from a noise perspective, but that will tend to make flash your primary or only light source, so you'll get the classic deer-in-the-headlights look with the background black or very dark. So a higher ISO is probably more useful to get somewhat better balance between foreground and background illumination.</p>

[jbq]

If you want the flash to be the primary source of light, you should probably be shooting in P or M mode (I typically go for ISO 400 1/100s f/5.6). If you want to balance flash and ambient (watch out for the color balance), Av or Tv will do.

 

My guess is that you're currently using the latter while you would prefer the behavior of the former.

[paul hart]

I have the same combination as you. In the circumstances you describe, I too find that M mode is best, working at about 1/100-125 and f5.6 or thereabouts. Let the flash do the rest. Gets it right 9 times out of 10.

[mark u]

You will probably get more pleasing images by shooting from further away using a longer focal length - this will allow you to use bounce flash which produces much softer and more even lighting. 8ft is fine, but at 4ft inverse square falloff from the flash will be fairly severe. If the ceiling isn't white or there is a strong colour cast from the walls, you may do better with a Lumiquest Pocketbounce rather than a diffuser and bouncing off the wall or ceiling.

 

Your 550EX has plenty of power for handling these situations - at 10ft (about 3m) you could use f/11 and still light the subject adequately at ISO 100 using direct flash at a 35mm or longer focal length, even with a shutter speed of 1/200th that would make the ambient exposure totally insignificant in typical indoor lighting. ISO 400 doubles the flash range, or probably equivalently makes up for light lost in using bounce flash.

 

You could usefully read the EOS flash bible here:

 

http://photonotes.org/articles/eos-flash/

[joe_bailey2]

Thanks for the responses. We have a family Christmas party tomorrow, with Santa, and it's my first time out with this camera. I haven't had time to experiment properly with higher ISO settings. I was concerned when I set the camera to M, ISO 400, 100 and 5.6; the level meter in the view finder was flashing at -2. I wasn't sure if I had something adjusted incorrectly. I'm coming from a G5 Powershot and it's a learning experience. Thanks...

[digitmstr]

>> the level meter in the view finder was flashing at -2. <<

 

That would be the AMBIENT light meter. In this case, it showed 2 stopd under. You can adjust the ratio between ambient and flash to taste.

[gluteal cleft]

This is a question that comes up very often, although it usually sounds a bit different. It's about the behavior of Canon SLRs and flashes in "Av" mode as opposed to other modes.

 

By default, in "Av" mode, Canon SLRs use the flash as fill, not primary light. That means that the camera will, before even thinking about the flash, decide on a shutter speed and aperture that will correctly expose the background *without* flash, then it will use the response from the TTL pre-flash to decide how much power to give the flash to light the subject.

 

The result is that you get large apertures and/or slow shutter speeds, because the camera wants to expose the background properly as well.

 

Luckily, there's a way around it. One of your custom functions will allow you to switch the sync speed in Av mode from auto to your max sync speed, probably 1/200 or 1/250. Once you've set it to your max sync speed, then the flash becomes your primary light, and you can set your aperture where you want it, and as long as your flash has enough power, e-TTL will take care of the rest.

 

Of cours, that means that as the subject-to-background distance increases, the less exposure the background will receive, it's not a *completely* free ride.

 

Oh... as for which ISO to use, I'd choose the lowest ISO with which your flash can still provide enough power for proper exposure. That does mean that the flash will work harder and go through batteries more quickly, but you do get a better image for the trouble. At the distances you mention, you'd need an awfully small aperture to need more than ISO 100.

 

steve