The Shutter Priority and Aperture Priority modes make good sense. You can guarantee certain outcomes. For example, if you want to be sure to always freeze motion or cause blur (in the case of Shutter Priority, shown as Tv (Time value) on your Canon. Or if you want to be sure your entire subject is within the depth-of-field in the case of Aperture Priority, shown as Av (Aperture value) on your Canon.


But what about using flash with the"Priority" modes?That introduces a veryhandy, butsometimes confusing feature. Theway theTv and Av modesutilize flash is for foreground fill only. Theaperture and shutter speeds shown are for the background light/ambient light quality. Therefore, when you get flashing values in your viewfinder, they indicate overexposure or underexposure of the background only. Remember, this is only for when a flash is activated. The flash acts independently, metering itself with the pre-flash, ensuring the proper exposure of the subject. Just remember to use your "FE Lock" button if your subject will be off-center. You can see my description of the "FE Lock" feature here.


I've divided up the examples in to two types. One demonstrating "Background Light" the other "Quality of Light". I've used rather mundane subject matter because in this post the lighting is the subject.


Both sets of examples were taken with a Canon XTi inShutter Priority (Tv) Mode, with the built-in flash on, 50mm f1.4 lens, ISO 100. I used Shutter Priority rather than Aperture Priority due to the fact that the exposure values in Aperture Priority required a tripod, and I wasn't in the mood.


"Background Light" "Quality of Light"


f1.4 1/30 f1.4 1/30


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f1.4 1/60 f1.4 1/60


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f1.4 1/125 f1.4 1/125


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f1.4 1/200 f1.4 1/200


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The "Background Light" examples were taken at 3pm, and the background light is quite easily manipulated with the shutter speed. I have included the "Quality of Light" examples to show what you may have noticed in the "Background Light" examples. Although the foreground is technically exposed properly, it has a different "quality", sort of a twilight/shrouded look to it. So when we discuss "background" lighting, we're really talking about the entire atmosphere that exists in the image. The flash meters off of real, physical items, not the existing light or darkness, or dust hanging in the air.


So in the "Quality of Light" images, you should notice that as the shutter speed increases, the darkness moves from the background, washes toward, then over, and surrounding the properly exposed foreground images. Pretty spooky. We've gone from mundane subject matter to evil subject matter in four frames.


Imagine the artistic possibilities with this kind of feature. What character would a portrait take on? Or an animal? Or wedding? (be careful with that one)