What's wrong with the AE system

[blithevincent]

Was practicing with my new 350D these days. However, I find when I use automatic mode or AV/TV mode, the histogram of the pics are not properly centered most of the times, which means pics are under-exposure for about 1/3 to 2/3 stops. This happens even when I shoot outside. And the exposure compensation is by default set to 0. I can not figure out what's wrong with the AE? Do I need to send the 350D to canon for check?

 

[saperboy]

I'm guessing there's nothing wrong with the camera. It's not unusual to get a an off-centered histogram, what's more important is not to get the graph spilling over to the left or right, that's when it's over or under exposed. Do take note of the lighting on your composition and at which part of the subject you're trying to focus on (dark to light tone), specially if your shooting at SPOT mode.

 

[napsack]

I don't think anything need to do with your camera. I used to own 350D it only has light histogram (30D or higher has both light & color histogram) light histogram only shows you the amount of light pixel in your picture.

Some picture, like shooting in snowy environment or strong sunlight you will have picture that has graph lay on right-most of histogram. (also depends on your EC) Dark scene is otherwise. Light histogram is a useful measurement tool but somehow for practice I encourage you to try out with your eye. Change setting of metering mode to partial mode then use AEL in different environment different light and you will notice thing that different.

Even though you shoot photo in sunny day but if your picture has a lot of shadow then light histogram will show graph on left-most side too.

 

[shinken]

A better understanding of the histogram can help eliminate some possibilities:

http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml
http://www.photozone.de/7Digital/index.html
http://www.sphoto.com/techinfo/histograms/histograms.htm
http://www.earthboundlight.com/phototips/histogram.html
http://www.cambridgeincolour.com/tutorials/histograms1.htm
http://www.outbackphoto.com/workflow/wf_41/essay.html
http://www.sphoto.com/techinfo/histograms/histograms.htm
http://www.zuberphotographics.com/page_PSHistogram.htm

After that, experiment with the exposure lock button to lock exposures at various parts of the image before deciding on focus point. See how changing the locked exposure helps to make the compensation you want.

 

[+evenstar]

you need to compensate when you're shooting objects that are not mid-tone