The concept of the camera being able to hold the shutter open to give you a realtime view of the scene and yet pause long enough to focus is impressive in terms of technology. And even more impressive is the quality of the live view that the 40D provides, which is smooth and detailed.
To create this live view, Canon engineered an electronic first-curtain shutter that enables shooting while the mechanical shutter is completely open. To give the detailed view, the camera uses a high-speed scanning and an electronic reset system that mimics the high-speed mechanical shutter operation. The system then synchronizes with the mechanical second-curtain shutter to create what Canon terms a slit exposure.
This technology enables some very cool side features as well. For example, because the first-curtain shutter is electronic, the shutter cocking noise can be reduced, and the 40D offers two modes for quiet or silent shooting in either Continuous or Single Shot drive modes. The caveat is that although Live View shooting has an admittedly high "coolness" factor, it comes at a price. With continual use of Live View shooting, the sensor heats up quickly, and the battery life diminishes markedly.
More specifically, here is what you can expect with Live View shooting:
♦ Temperature affects the number of shots you can get using Live View. With a fully charged BP-511A battery, you can expect 180 shots without flash use and approximately
170 shots with 50 percent flash use in 73-degree temperatures. In freezing temperatures, expect 140 shots without flash use and 130 shots with 50 percent flash use per charge. With a fully charged battery, you'll get approximately 30 minutes of continuous Live View shooting before the battery is exhausted.
♦ High ambient temperatures, high ISO speeds, or long exposures can cause digital noise or irregular color in images taken using Live View. If you see a warning icon on the LCD, discontinue shooting and let the camera's internal temperature cool down. If you disregard the warning, the camera will eventually stop shooting until the internal temperature decreases.
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