Canon EOS 50D Exposure
The Canon 50D provides a great deal of control functionality, leaving you the choice of going on fully automatic settings, or making fine-tuned adjustments as desired. 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 two Custom modes, which users can program for quick access to their favorite functions. 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 50D into a very easy to use point-and-shoot camera, albeit a very capable one.
New to the 50D is a new "Creative Auto" mode, which attempts to make complex photographic functions like depth-of-field easier to use. The camera controls focus and general exposure, but leaves it up to the user to adjust the level to which background elements are in focus, and whether to freeze or blur motion.
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 Canon 50D 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 Canon 50D 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 50D Metering & ISO Sensitivity Options
Exposure metering options include Evaluative, Partial (9% of viewfinder at center), Spot (3.8% of viewfinder at center), and Center-weighted options. The Canon 50D's Exposure Compensation setting allows the user to increase or decrease the metered exposure by up to two stops positively or negatively, in one-third or one-half EV increments.
The Canon 50D offers regular ISO equivalents of 100, 200, 400, 800, 1,600, and 3,200, with the option to use fractional settings in 1/3-EV increments (100, 125, 160...). The 50D also offers two additional high-range ISO settings: H1 is equivalent to ISO 6,400 and H2 takes the camera to 12,800.
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 0.7 EV, and then have the camera give you a variation of +/- 2/3 EV around that point.
AE/FE Lock (" * " button)
The Canon 50D has the same simplified AE Lock button as the 40D, which unbundled the AF Lock feature from the old button on the older EOS cameras like the 20D and 30D. Marked with an asterisk (*) symbol, the AE Lock button simply holds the exposure at one setting while you recompose the image. It's very useful when spot metering, but also when dealing with subjects where you want to draw your exposure from one place, while autofocusing on another. Pressing the button with the pop-up flash activated or with an external flash mounted activates the FE Lock (Flash Exposure) function, which fires the flash and locks the proper exposure for the following frame.
The AF-ON button allows you to set focus before depressing the shutter button. With Custom Functions, you can reprogram the behavior of the AF-ON button, as well as swap functions with the AE/FE Lock button. Autofocus action can either replicate that of the standard half-press of the shutter button, or be transferred completely to the AF-ON button, making the shutter button responsible for controlling AE lock only.
The AF-ON button also controls autofocus operations in Live View mode. The Canon 50D now has two styles of autofocus operation in Live View mode: the standard phase detection method, which requires the reflex mirror to be briefly swung back into the optical path, thus disrupting the live view briefly, or a contrast detection method which does not. Both methods have their advantages and disadvantages, but the contrast-detect method offers an uninterrupted user experience. A third method incorporates a face detection into the contrast detection method, offering the face-detecting mode of autofocus now commonly seen on consumer point-and-shoot cameras.
White Balance Options
The Canon 50D 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 Canon 50D 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 50D's Continuous Shooting mode is rated by Canon at 6.3 frames per second in high speed mode, for a total of 60 Large/Fine JPEG shots or 16 RAW before the buffer fills; or 3 frames per second in low speed mode. These results come when using a regular CompactFlash card; the 50D is capable of using UDMA CompactFlash cards, and doing so improves the buffer throughput of the camera. With a UDMA card, the Canon 50D can shoot up to 90 Large/Fine JPEG shots before the buffer fills; the number of RAW images is unchanged at 16. The number of consecutive shots could be limited by CompactFlash space, if your memory card is nearly full. Also, when shooting JPEGs of a very complex scene with a lot of sharp, fine detail may also compress less and result in lower buffer capacities.
The camera's Drive setting also accesses two Self-Timer modes, which open the shutter 10 or 2 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.