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Photography Question 

MaryAnn L. Oakland 		 

Dark background when using flash attachment


 
 
We bought a new flash attachment for our Canon EOS Digital Rebel camera but I notice that the backgrounds all seem dark. The people are nicely lit except for their faces are pretty bright, but the backgrounds are dark. Is it because it is such a powerful flash, it is a Canon Speedlite 550EX. Should I use bounce flash? Change the shutterspeed? We will be taking wedding photos in July and I don't want to have dark backgrounds, I would like an evenly exposed photo.Thanks.
MaryAnn


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April 05, 2004

 

Jon Close 		  The light from a flash dissipates quickly (with the inverse of the square of the distance from its source), so that it properly exposes a near subject, but adds little or no light to the background.

The flash exposure is controlled with a combination of aperture and the TTL circuitry limiting the speedlight's output. The background exposure is controlled by the shutter speed and aperture.

Using the flash in green box and P modes the EOS cameras generally set a faster/hand-holdable shutter speed of 1/60-1/125 and wide open aperture. With a f/3.5-5.6 zoom and ISO 100 that does not give much exposure to the background.

To give more exposure to the background you need to use a slower shutter speed, and/or set a higher ISO setting. Switching to Tv, Av, or M modes you can set slower shutter speeds. The use of the meter scale changes when you shoot flash in these modes. Green box and P modes are full auto "snap shooter" modes, so the meter scale reads "0" ("correct" exposure) even though the background is underexposed. In Tv, Av, and M modes, the meter reads the ambient exposure without regard to the light the flash provides. You can set the shutter and aperture to give equal exposure to the background and flash subject ("0") or leave the background slightly darker at -1 or -2 to accentuate your flash-lit subject. Note that longer shutter speeds to give more background exposure may also require a tripod and a notice to your subjects to not move for up to a second after the flash fires.

Changing the ISO setting from 100 to 400 will lighten the background by 2 stops without changing the shutter speed or the flash exposure of the near subject. You will have the issue of increased grain/noise at higher ISO.

If you are very close to your subject the TTL circuitry cannot quelch the flash fast enough to prevent the subject from being overexposed, so you either need to take a step back, or set a smaller aperture for close shots with the flash. When shooting in Tv, Av, and M modes the 550EX will display a scale showing the minimum and maximum flash to subject distances that it can properly expose.

Some useful documentation on using the Canon flash system can be found at

http://www.camera.canon.com.my/archive/photography/art/art13/index.htm

http://www.bobatkins.com/photography/eosfaq/flashfaq.htm

http://www.camera.canon.com.my/archive/photography/art/art13/index.htm


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April 05, 2004

 

MaryAnn L. Oakland 		  Thank you, you have very helpful!! I will definitely check out those websites.


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April 05, 2004

 

Derek Holyhead 		  Hi,
This may interest you also:
http://revolution.cx/rcx/fecset.htm
Regards,
del


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April 05, 2004

 
- Gregory LaGrange

BetterPhoto Member
Contact Gregory LaGrange
Gregory LaGrange's Gallery 		  Bouncing it off the ceiling will keep the background from being so dark also.


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April 05, 2004

 
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