Contrast detection is slow and may hunt back and forth, so this method should be reserved for methodical work such as macro or still life. Two flavors of autofocus can be used in live view: by contrast detection nearly anywhere on the screen, or by a momentary flip down of the mirror to allow the conventional phase-detection AF sensors, which can employ face detection, to focus the image. Once you enable it in the menu, a press of the Set button flips up the mirror and sends the image from the sensor to the big 3-inch, 230,000-dot LCD (a hand-me-down from the top-of-the-line EOS-1Ds Mark III). Live view works similarly to that of the EOS 40D. And, the finder has been brightened by use of better mirror coatings and a more transmissive focusing screen. Moreover, the readouts below the finder screen can be seen along with the entire frame image, in contrast to the XTi’s now-you-see-them-now-you-don’t readouts that were a particular pain for eyeglass wearers. Our actual Lab measurement, though, comes out even better, to 0.95X. Canon says the magnification of the pentamirror finder has been increased to 0.87X, from 0.80X of the XTi. The XSi makes composing images easier on two fronts: an upgraded optical finder, and the addition of live view. (Fast lenses, with their shallower depth of field wide open, benefit from a high-precision sensor.) Our AF test of the XSi showed it to be about the same speed as the XTi in bright to medium light, and somewhat faster at the lowest light levels. The XSi does get a high-precision central cross sensor for f/2.8 and brighter lenses. Also speeding up the shooting is the 9-point autofocusing, essentially the same as the XTi’s, which was already the fastest in class and one of the fastest in any DSLR. It can continue firing single RAW frames every second or so after that. The camera is rated for bursts of up to 6 RAW or 4 RAW + JPEG, which we found accurate. But the XSi would keep on firing at just under 2.5 fps until the card filled up. (The new Olympus E-420 and E-520, both 10MP models, are rated at 3.5 fps up to the capacity of the card, and we will test that claim very soon.) Using a 2GB Panasonic Class 6 SD card, we got 53 and occasionally 54 frames at about 3.6 fps. The first Rebel to get Canon’s DIGIC III processor, the XSi is currently the quickest-firing 12MP camera in this class, rated at 3.5 frames per second, and for highest-quality JPEGs, up to 53 frames.

Canon xsi liveview