Sunday, July 12, 2009

G9: Exposure and Flash Compensation in Av Mode

The previous post showed the effects of combinations of exposure and flash compensation on a typical indoor scene when the G9 was using its built-in flash and operating in Program mode. This post shows the results of those same combinations when the G9 is operating in Aperture Priority (Av) mode. For these photos, I selected f5.6 to get away from the largest aperture (f2.8) that was often the automated selection in Program mode.

In Av mode, the photographer manually sets the aperture and the G9 selects the shutter speed to give the “correct” exposure (according to the G9). Simple enough, but there are a few peculiarities and precautions. The G9’s choice for shutter speed is based on ambient light; however, similar to Program mode, Av mode will lock into 1/60 second as the slowest shutter speed if Slow Sync is turned OFF in the menu. Because the photographer has already locked the aperture, this means that exposure compensation is actually rendered inactive when the flash is turned on if the G9 is in Av mode with Slow Sync OFF. Figure 3 (continuing the numbering from the previous post) illustrates this limitation.

Figure 3

Although nine photos were taken, there are really only three different photos in Figure 3 because there actually was no exposure compensation – only flash compensation.

With Slow Sync ON, there are nine different photos resulting from this bracketing as shown in Figure 4 below.

Figure 4

Again it is obvious from these two examples that the Exposure Compensation and Flash Compensation values are not intended to summed to provide a basis for comparison. In fact, sometimes Exposure Compensation doesn’t actually do anything!

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