flash with slow shutter?

[abel]

i was thinking... are there benefits of using a 420ex or 550ex flash during night time shots. im assuming say for instance with a building in the background and a tree in the foreground. using the flash to lighten the tree and have a longer shutter speed to allow enough light in to make the background decent...

im not sure if this even makes sense but it was something i thought about... one of those "newbie moments" hehe

all comments and suggestions are welcomed.

thanks

[Jesper]

If you put your camera on Av mode, that's exactly what's going to happen. The camera will determine the shutter speed for the ambient light and you'll get a slow shutter speed. This is what the manual of my 10D says on page 97:

"Select Av mode to manually set the aperture value. In low-light conditions against a background such as a night sky, you can use automatic slow-sync settings to properly expose the main subject and the background. The main subject is captured by the flash, and the background is captured by long exposure using a slow shutter speed."

[abel]

thanks for the info jesper... i really appreciate it...

ill give it a try tonight...

[scottbergerphoto]

You can use Av, Tv, or M. It doesn't matter. Flash is really a compilation of two exposures: 1. Flash for the foreground and 2. The Shutter and Aperture settings you choose for the background. Most program modes have a low shutter speed limit of 1/60 of a sec. That's not slow enough to expose a dimly lit background. If you want to capture background exposure in Program Mode you have to use the "slow sync" option, also known as Night Portrait".
In Summary, to capture ambient light exposure when using flash:
1. Set your exposure for the ambient light using the camera meter or a hand held meter in Av, Tv, or M modes. (Alternately set the camera to P and Night Portrait).
2. Turn on the flash.
3. Use a tripod.
4. Tell your subject not to move until you hear the shutter close. This is longer then the flash duration.

For a more detailed discussion of the use of flash and ambient light , I suggest "Mastering Flash Photography" by Susan McCartney.
Regards,
Scott

[PacAce]

Just wanted to add a side note. For the DRebel and the 10D, setting the camera to P mode will set the minimum shutter speed to 1/60 when using the flash.

And, for the 10D, setting the mode to Av with CFn-03 set to 1 will automatically set the shutter speed to 1/200 when using the flash.