BetterPhoto Q&A
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Problems with Exposure on EOS 10D

I am shooting with a Canon EOS 10D with a 28-135 IS USM lens. Ive only just got the camera and dont understand the following scenario.

I'm shooting in my house on a fixed subject that is not lit brilliantly.
On pure autofocus the shutter speed is 1/60th and aperture 5.6.

When I set the camera to Tv and set the shutter speed to 1/60th the aperture is 5.6, BUT its flashing. When I look in the manual it says redude the shutter speed. I reduce it to 1/6th and the aperture stops flashing.

Why am I getting 2 completely different results, AUTOFOCUS: 1/60th at 5.6
Tv : 1/6th at 5.6

I can obviously shoot with a flashing aperture, but I have been testing this with over 100 photos and the problem only occurs in dimly lit conditions

I am using the pop up flash and not the 550EX

Please help

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April 19, 2004

In the full auto modes the speedlight (whether the built-in pop-up or the accessory 550EX) will be the primary light source. The camera sets a high, hand-holdable shutter speed of 1/60. The near subject will be properly exposed by the flash, but the background will be dark/underexposed. The meter reads proper exposure ("0") because this is typical expected result for snapshot-style flash picture in full auto.

In the "creative modes" Tv, Av, and M the meter reverts to reading the ambient light without regard to the flash. The flash will provide only fill light rather than be the main source. At a shutter speed of 1/6 and f/5.6 the background would be properly exposed for the ambient light. The flash output is controlled by the E-TTL flash metering and will give the same exposure to your near subject, regardless of the shutter speed.

For more information on the EOS flash system, see:
http://www.bobatkins.com/photography/eosfaq/flashfaq.htm

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

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

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April 20, 2004