Metering
DSLRs offer evaluative, spot and center-weighted averaging metering modes. Manufacturers implement them with variations, but the consensus seems to be that these three need to appear on a menu or switch. The Canon 50D offers one more mode it calls “Partial,” which could be considered a bastard offspring of spot and center-weighted. It measures the central 9 percent of the field – not selective enough to be useful as a spot, and lacking any sensitivity toward the edges.
 

Both the Canon 50D and the Olympus E-30 default to evaluative metering. Evaluative systems simultaneously take many readings across the frame, and run the values through an algorithm that recognizes typical situations, such as bright skies, extreme contrast or flat lighting, and accommodates them. 

Evaluative/Overall Metering

Olympus EVOLT E-30	Canon EOS 50D

Both cameras generally delivered good, even exposures in Evaluative mode when shooting scenes lit from above (indoors or outside), but faltered similarly in more challenging lighting - like the back-lit scene shown above.

Switching the cameras to Center-Weighted metering had little bearing on their overall rendering of the silhouetted subject. Both the E-30 and 50D treated the scene nearly identically in Center-Weighted and Evaluative metering modes, retaining little visible detail in the centered subject. The cameras have similarly given priority to the background information in both photos.

Center-Weighted Metering

Olympus EVOLT E-30	Canon EOS 50D

Photographing the scene in Spot metering mode, both cameras captured brighter exposures with a similar shift apparent in the highlight portion of their histograms. The distinction between the two cameras shows in the Canon’s slightly brighter treatment of the mid-tone values. Since the subject’s forehead and cheek falls in this zone, more of his expression comes across in the shot from the Canon (below).

 Spot Metering

Olympus EVOLT E-30	Canon EOS 50D

The Partial metering mode included on the Canon 50D performed as advertised, generating an exposure that fell between its Center-Weighted and Spot settings. Unfortunately, the reading was closer to the Center-Weighted setting, and reproduced the dark subject with virtually no detail.  

Partial Metering

Canon EOS 50D