Canon Rebel XTi Exposure
The Canon Digital Rebel XTi provides as little or as much exposure control as you could want. Standard exposure modes include the usual Program, Aperture-Priority, Shutter-Priority, and full Manual modes, as well as some "Image Zone" (scene-based preset) modes, and an Automatic Depth-of-Field mode. The "Image Zone" exposure modes include Portrait, Landscape, Close-up (macro), Sports, Night Portrait, and Flash Off modes. These modes preset a variety of camera parameters to make it easier for non-expert photographers to achieve good exposures in a variety of standard shooting situations. The Flash Off mode simply disables the flash and external Speedlite (if attached), and puts the camera under automatic exposure control. The full Auto mode takes over all camera functions, turning the Canon Rebel XTi into a very easy to use point and shoot camera, albeit a very capable one.
The Aperture Priority and Shutter Priority modes work much the same as on any other camera, allowing you to adjust one exposure variable while the Rebel XTi selects the other for the best exposure. Program mode keeps both variables under automatic control, while Manual mode gives you full control over everything. The Automatic Depth-of-Field mode (A-DEP) uses all nine autofocus zones to determine the depth of field in the active subject area. Once the Rebel XTi has determined the range of focusing distances present across the nine zones, it automatically computes the combination of aperture and shutter speed needed to render the nearest and furthest points in sharp focus.
Canon Rebel XTi Metering & ISO Options
Exposure metering options are similar to the 300D and 350D models, with Evaluative, Partial, and Center-Weighted options. The Canon Rebel XTi offers variable light sensitivity, with ISO equivalents of 100, 200, 400, 800, and 1,600. For adjusting the exposure, the XTi's Exposure Compensation setting increases or decreases overall exposure from +/-2 EV in one-third or one-half EV increments. (You set the step size through the Custom menu.) An automatic exposure bracketing feature lets you set the total exposure variation (across three shots) at anywhere from +/- one-third or one-half EV all the way up to +/- 2 EV. The nice part is that the automatic variation is centered around whatever level of manual exposure compensation you have dialed in. Thus, you could manually set a positive exposure compensation of 0.7EV, and then have the camera give you a variation of +/- 2/3 EV around that point.
Another feature deserving comment is the Rebel XTi's separation of the autoexposure and autofocus lock functions. In consumer-level digital cameras, half-pressing the Shutter button locks exposure and focus simultaneously. You can use this to deal with an off-center subject by pointing the camera at the subject, locking exposure and focus, and then reframing the picture before finally snapping the shutter. The only problem is that you sometimes need to perform a more radical recomposition of the subject in order to determine the proper exposure. For instance, you may want to zoom in on the subject, grab an exposure setting, and then zoom back out before taking the picture. Situations like that require locking the exposure independently of the focusing, and the Canon Rebel XTi provides for just such eventualities by way of a separate AE lock button on the back of the camera, right under your right thumb. Through the Rebel XTi's Custom menu, you can specify the operation of the AE Lock button, as well as the AF/AE locking function of the Shutter button. A very handy feature indeed.
White Balance Options
The Canon Rebel XTi offers a full range of White Balance settings, including six presets, an Auto setting, and a Custom setting. The six presets include Daylight, Shade, Cloudy, Tungsten, Fluorescent, and Flash. The Custom setting bases color balance on a previous exposure, meaning you can snap an image of a white card and then base the color temperature on that image. A White Balance bracketing option snaps only one image, then writes three successive files from that single image. Bracketing steps are from -/+ 3 stops in whole-stop increments. (Each stop corresponds to five mireds of a color conversion filter, for a total range of +/- 15 mireds. This corresponds to about a +/- 500K shift at a normal daylight color temperature of 5,500K.)
The WB Bracketing is set on the same grid as the White Balance correction grid. Fairly sophisticated, the white balance correction tool lets you shift the color balance toward more or less green, amber, magenta, or blue, using a +/-9 step grid format. You move a highlighted square through the grid to adjust the color balance. It's a slightly more advanced interface than I'm used to seeing on digital cameras, but a useful one that greatly extends the camera's color corrective abilities.
The Rebel XTi also offers a Picture Style option through the LCD menu, which lets you select from Standard, Portrait, Landscape, Neutral, Faithful, Monochrome, or three User Defined settings. In each of the preset modes, the contrast, saturation, sharpness, and tone are set for specific conditions. The three User Defined options let you manually adjust each variable, then save it as a custom parameter. Finally, you can set the camera's color space to sRGB or Adobe RGB.
Continuous Shooting Mode and Self-Timer
The Canon Rebel XTi's Continuous Shooting mode is rated by Canon at three frames per second, for a maximum of 27 frames. Do note, though, that the number of consecutive shots could be limited by CompactFlash space, if your memory card is nearly full. Very complex images with a lot of sharp, fine detail may also compress less and result in lower buffer capacities.
The camera's Drive setting also accesses a Self-Timer mode, which opens the shutter 10 seconds after the Shutter button is pressed, giving you time to dash around in front of the camera. A Remote Control mode works with the dedicated and wireless remote units as well.