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Photography Question 

Barbara Helgason
 

Need help solving this shutter speed mystery!


My camera is the Canon Rebel XT.
Why do I get a faster shutter speed when I am shooting in automatic compared to when I shoot in the creative zone, av priority for example. In both cases I am using the same aperture and the same ISO! Both captures are correctly exposed. What am I missing here? I am finding myself turning to automatic more and more often just to get a faster shutter speed which allows me to work without a tripod. And that after I spend so much time learning to use the creative zones correctly. If anyone can explain this to me it would be greatly appreciated!


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November 23, 2005

 
- Gregory LaGrange

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  Changing modes probably changes the metering pattern from evaluative to center weighted.


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November 23, 2005

 

Bob Cammarata
  Try setting to full-manual and see if you can duplicate exactly what your automatic settings would yield.
This will help you to better understand how your machine "thinks" and how it reacts to what it sees.


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November 24, 2005

 

Jon Close
  The differences in exposure settings when switching from Basic Zone to Creative Zone is probably due to different ISO settings. In the Basic Zone exposure modes the Digital Rebel is setting ISO automatically, ranging from 100 to 400. In the Creative Zone, ISO is set manually and is probably defaults to 100 unless you've changed it. So that can result in different shutter speeds and apertures when switching from Basic to Creative while still getting the same exposure.

In addition, there is a difference in the way the different modes function with flash. In most of the Basic Zone modes (icons and green box) and P, the camera sets a relatively high shutter speed (1/60+) when using the flash. This allows handheld shooting and the flash is the main light giving good exposure to your subject (so long as they are within the usable range of the flash) without regard to the exposure of the background.

In Av, Tv, and M with flash, the metering is with respect to the ambient light without regard to the flash and the flash is set to provide fill light. This gives a more natural balance of exposure to your near subject and the background. In typical dim indoors, Av will set long shutter speeds, and Tv will typically peg the lens aperture wide open unless a longer shutter speed is selected. For more information on using flash with EOS cameras, see http://photonotes.org/articles/eos-flash/.


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November 24, 2005

 

Barbara Helgason
  Wow, thanks guys, Gregory you are right, the metering would affect the shutter speed as well. I had it set to evaluative in av mode which is what it is also set in during the auto modes.

Bob, I am going to give your suggestion a try and see where that gets me.

And Jon, I realize I have alot to learn about the flash, didn't know it was the main light in auto and a fill in creative modes. That certainly explains some things to me. I'm going to check out this article right now.

Thanks again guys, for your help!!


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November 24, 2005

 

Christopher A. Vedros
  All the suggestions above are correct.

Another thing you might check is the exposure compensation. If you inadvertantly set EC, it would effect the creative modes, but not the auto modes. Just something else to check.

Chris


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November 24, 2005

 
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