Canon 7D exposure problems

<p>So I have a Canon 7D and I am suddenly having an exposure problem in the auto modes.</p>

<p>Right now I am using the Canon EF 24-105mm L IS USM. I'm in a room with medium lighting and focusing on a can of pepsi about 18 inches away at 4.0 with an ISO of 100, and the built-in flash activated. When I depress the shutter button, it sets my shutter speed to 1 second! The exposure seems to be basically correct, but I don't understand why it's setting such a long shutter speed.<br>

If I switch to manual mode, I can get the same exposure at 1/250th.<br>

The built-in flash settings are set to E-TTL II and the exposure compensation is set to 0.</p>

<p>It was working fine a couple of days ago, not sure what could have happened. Does anybody have any ideas?</p>

<p>Thanks</p>

<p>I forgot to mention, that was in aperture priority mode. I have the same exposure problem in shutter priority mode as well. In full auto mode it gives better results with a shutter speed of 1/60th.</p>

<p>You are in Aperture Priority mode (Av), right?</p>

<p>I seem to recall this is fairly normal behavior. The standard way the camera tries to expose with flash in Av is to keep the shutter open long enough to expose for the background, basically making the flash a "fill". It is on page 115 of the Firmware 2.x manual.</p>

<p>There is a custom function that you can use to restrict the shutter speed for flash in Av mode: C. Fn I-7 "Flash sync. speed in Av mode" (p. 223). The available settings are:</p>

<ul>

<li>0: Auto - what you are seeing</li>

<li>1: 1/250-1/60 Auto</li>

<li>2: 1/250 sec. (fixed)</li>

</ul>

<p>The asterisk for setting 0 reads: "Normally, the sync speed is set automatically within 1/250 sec. to 30 sec. to suit the ambient brightness. In low light, the main subject is exposed with the flash, and the background is exposed with a slow shutter speed set automatically..."</p>

<p>In Tv mode (shutter priority), the shutter speed is manually set by you between 1/250 - 30 sec. Not sure what you are seeing there...</p>

<p>It appears that you are correct. I don't know why I thought it worked differently before. I guess it was in different ambient lighting conditions. Setting the "Flash sync speed in Av mode" to 1/250-1/60th works great.<br>

The problem I am having in shutter priority mode is that, for instance, if I set the shutter speed to 1/60th, the aperture setting will blink 4.0 which is the lowest setting, which I believe means that it wants to go lower. But I will still get a good exposure.<br /><br />I guess I just misunderstood what the camera is expected to do with the exposure when using the flash.<br>

Thanks for the insight.</p>

In Tv mode, with ETTL flash, the camera is trying to expose for ambient light and use flash as fill (as described by Larry above). In Tv mode the aperture can't get any wider than the maximum aperture of the lens, so the aperture indicator blinks showing underexposure. Note that while there is less ambient exposure than what the meter thinks it needs, the flash should provide adequate light on the main subject. If the image is taken at 1/60th @ f4 when using ETTL flash, irregardless of what mode you used to obtain those settings (Av, Tv, P, or M), the exposure should be identical.

 

For Canon, it is easier to use Manual mode when flash is providing the main source of light. The aperture and shutter speed are then used to control how much ambient light will impact the image while the ETTL flash system provides the main source of light. I generally use Av or Tv mode when ambient is the main source of light and flash is used for fill.

<p>Yep, Av is designed to expose correctly for ambient light and use flash to fill in the shadows for a natural appearance. It's actually my favorite flash mode. However in really dim light you need to crank ISO or use a tripod to properly blend ambient and flash.</p>

<p>Use M mode if you need to control ambient and flash exposure separately, e.g., let background go dark and use flash as main light. P mode will do this automatically in dim light</p>

<p>Check the lens first, what I think your lens ( Canon EF 24-105mm L IS USM ) got its common diaphragm malfunction. </p>