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Be aware that if you've activated Highlight tone priority (described later), the H setting (and ISO values less than ISO 200) will not be available even if you have enabled ISO expansion.

Figure 3.48 This enlargement shows that noise levels can be acceptable even at ISO 6400.

C.Fn I-03: Flash Synchronization Speed When Using Aperture-Priority

Flash sync. speed in Av mode. You'll find this setting useful when using flash. When you're set to aperture-priority mode (Av), you select a fixed f/stop and the Rebel T2i chooses an appropriate shutter speed. That works fine when you're shooting by available light. However, when you're using flash, the flash itself provides virtually all of the illumination that makes the main exposure, and the shutter speed determines how much, if any, of the ambient light contributes to a second, non-flash exposure. Indeed, if the camera or subject is moving, you can end up with two distinct exposures in the same frame: the sharply defined flash exposure, and a second, blurry "ghost" picture created by the ambient light.

If you don't want that second exposure, you should use the highest shutter speed that will synchronize with your flash (that's 1/200th second with the Rebel T2i). If you do want the ambient light to contribute to the exposure (say, to allow the background to register in night shots, or to use the ghost image as a special effect), use a slower shutter speed. For brighter backgrounds, you'll need to put the camera on a tripod or other support to avoid the blurry ghosts.

■ 0: Auto. The T2i will vary the shutter speed in Av mode, allowing ambient light to partially illuminate the scene in combination with the flash exposure, as at right in Figure 3.49. Use a tripod, because shutter speeds slower than 1/60th second may be selected.

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Figure 3.49 At left, a 1/200th second shutter speed eliminated ambient light so only the flash illuminated the scene; at right, a 1/60th second shutter speed let the ambient light supplement the electronic flash.

Figure 3.49 At left, a 1/200th second shutter speed eliminated ambient light so only the flash illuminated the scene; at right, a 1/60th second shutter speed let the ambient light supplement the electronic flash.

■ 1: 1/200-1/60 sec. (auto). The camera will use a shutter speed from 1/200th second (to virtually eliminate ambient light) to 1/60th second (to allow ambient light to illuminate the picture). This compromise allows a slow enough shutter speed to permit ambient light to contribute to the exposure, but blocks use of shutter speeds slower than 1/60th second, to minimize the blurriness of the secondary, ambient light exposure.

■ 2: 1/200th sec. (fixed). The camera always uses 1/200th second as its shutter speed in Av mode, reducing the effect of ambient light and, probably, rendering the background dark.

C.Fn II-04: Reducing Noise Effects at Shutter Speeds of One Second or Longer

Long exposure noise reduction. Visual noise is that graininess that shows up as multicolored specks in images, and this setting helps you manage it. In some ways, noise is like the excessive grain found in some high-speed photographic films. However, while photographic grain is sometimes used as a special effect, it's rarely desirable in a digital photograph.

The visual noise-producing process is something like listening to a CD in your car, and then rolling down all the windows. You're adding sonic noise to the audio signal, and while increasing the CD player's volume may help a bit, you're still contending with an unfavorable signal to noise ratio that probably mutes tones (especially higher treble notes) that you really want to hear.

The same thing happens when the analog signal is amplified: You're increasing the image information in the signal, but boosting the background fuzziness at the same time. Tune in a very faint or distant AM radio station on your car stereo. Then turn up the volume. After a certain point, turning up the volume further no longer helps you hear better. There's a similar point of diminishing returns for digital sensor ISO increases and signal amplification as well.

These processes create several different kinds of noise. Noise can be produced from high ISO settings. As the captured information is amplified to produce higher ISO sensitivities, some random noise in the signal is amplified along with the photon information. Increasing the ISO setting of your camera raises the threshold of sensitivity so that fewer and fewer photons are needed to register as an exposed pixel. Yet, that also increases the chances of one of those phantom photons being counted among the real-life light particles, too.

Fortunately, the Rebel T2i's sensor and its digital processing chip are optimized to produce the low noise levels, so ratings as high as ISO 800 can be used routinely (although there will be some noise, of course), and even ISO 1600 can generate good results.

A second way noise is created is through longer exposures. Extended exposure times allow more photons to reach the sensor, but increase the likelihood that some photosites will react randomly even though not struck by a particle of light. Moreover, as the sensor remains switched on for the longer exposure, it heats, and this heat can be mistakenly recorded as if it were a barrage of photons. This Custom Function can be used to tailor the amount of noise-canceling performed by the digital signal processor.

■ 0: Off. Disables long exposure noise reduction. Use this setting when you want the maximum amount of detail present in your photograph, even though higher noise levels will result. This setting also eliminates the extra time needed to take a picture caused by the noise reduction process. If you plan to use only lower ISO settings (thereby reducing the noise caused by ISO amplification), the noise levels produced by longer exposures may be acceptable. For example, you might be shooting a river spilling over rocks at ISO 100 with the camera mounted on a tripod, using a neutral density filter and long exposure to cause the pounding water to blur slightly, as shown in Figure 3.50. To maximize detail in the non-moving portions of your photos, you can switch off long exposure noise reduction. Because the noise-reduction process used with settings 1 and 2 effectively doubles the time required to take a picture, this is a good setting to use when you want to avoid this delay when possible.

■ 1: Auto. The Rebel T2i examines your photo taken with an exposure of one second or longer, and if long exposure noise is detected, a second, blank exposure is made and compared to the first image. Noise found in the "dark frame" image is subtracted from your original picture, and only the noise-corrected image is saved to your memory card.

■ 2: On. When this setting is activated, the T2i applies dark frame subtraction to all exposures longer than one second. You might want to use this option when you're working with high ISO settings (which will already have noise boosted a bit) and want to make sure that any additional noise from long exposures is eliminated, too. Noise reduction will be applied to some exposures that would not have caused it to kick in using the Auto setting.

n Tip

While the "dark frame" is being exposed, the LCD screen will be blank during Live View mode, and the number of shots you can take in continuous shooting mode will be reduced. White balance bracketing is disabled during this process.

When lower ISO settings are used, as in this 30-second exposure of the

Virgin River in Zion National Park (made through a neutral density filter), long exposure noise reduction might not be needed.

C.Fn II-05: Eliminating Noise Caused by Higher ISO Sensitivities

High ISO speed noise reduct'n. This setting applies noise reduction that is especially useful for pictures taken at high ISO sensitivity settings. The default is 0 (Standard noise reduction), but you can specify 1 (low) or 2 (strong) noise reduction, or disable noise reduction entirely. At lower ISO values, noise reduction improves the appearance of shadow areas without affecting highlights; at higher ISO settings, noise reduction is applied to the entire photo. Note that when the 2: Strong option is selected, the maximum number of continuous shots that can be taken will decrease significantly, because of the additional processing time for the images.

■ 0: Standard. At lower ISO values, noise reduction is applied primarily to shadow areas; at higher ISO settings, noise reduction affects the entire image.

■ 1: Low. A smaller amount of noise reduction is used. This will increase the grainy appearance, but preserve more fine image detail.

■ 2: Strong. More aggressive noise reduction is used, at the cost of some image detail, adding a "mushy" appearance that may be noticeable and objectionable. Because of the image processing applied by this setting, your continuous shooting maximum burst will decrease significantly.

■ 3: Disable. No additional noise reduction will be applied.

C.Fn II-06: Improving Detail in Highlights

Highlight tone priority. This setting concentrates the available tones in an image from the middle grays up to the brightest highlights, in effect expanding the dynamic range of the image at the expense of shadow detail. You'd want to activate this option when shooting subjects in which there is lots of important detail in the highlights, and less detail in shadow areas. Highlight tones will be preserved, while shadows will be allowed to go dark more readily (and may exhibit an increase in noise levels). Bright beach or snow scenes, especially those with few shadows (think high noon, when the shadows are smaller) can benefit from using Highlight tone priority.

■ 0: Disable. The Rebel T2i's normal dynamic range is applied.

■ 1: Enable. Highlight areas are given expanded tonal values, while the tones available for shadow areas are reduced. The ISO 100 sensitivity setting is disabled and only ISO 200-ISO 6400 are available. You can tell that this restriction is in effect by viewing the D+ icon shown in the viewfinder, on the ISO selection screen, and in the shooting information display for a particular image.

C.Fn III-07: Activation of the Autofocus Assist Lamp

Activation of autofocus assist beam. This setting determines when the AF assist lamp in the camera or an external flash is activated to emit a pulse of light prior to the main exposure that helps provide enough contrast for the Rebel T2i to focus on a subject.

■ 0: Emits. The AF assist light is emitted by the camera's built-in flash whenever light levels are too low for accurate focusing using the ambient light.

■ 1: Does not emit. The AF assist illumination is disabled. You might want to use this setting when shooting at concerts, weddings, or darkened locations where the light might prove distracting or discourteous.

■ 2: Only external flash emits. The built-in AF assist light is disabled, but if a Canon EX dedicated flash unit is attached to the camera, its AF assist feature (a flash pulse) will be used when needed. Because the flash unit's AF assist is more powerful, you'll find this option useful when you're using flash and are photographing objects in dim light that are more than a few feet away from the camera (and thus not likely to be illuminated usefully by the Rebel T2i's built-in light source). Note that if AF-assist beam firing is disabled within the flash unit's own Custom Functions, this setting will not override that.

■ 3: IR AF assist beam only. Canon dedicated Speedlites with an infrared assist beam can be set to use only the IR assist burst. That will keep other flash bursts from triggering the AF-assist beam.

C.Fn III-08: Whether It Is Possible to Lock Up the Viewing Mirror Prior to an Exposure

Mirror lockup. The Mirror lockup function determines whether the reflex viewing mirror will be flipped up out of the way in advance of taking a picture, thereby eliminating any residual blurring effects caused by the minuscule amount of camera shake that can be produced if (as is the case normally) the mirror is automatically flipped up an instant before the actual exposure. When shooting telephoto pictures with a very long lens, or close-up photography at extreme magnifications, even this tiny amount of vibration can have an impact.

You'll want to make this adjustment immediately prior to needing the mirror lockup function, because once it's been enabled, the mirror always flips up, and picture taking becomes a two-press operation. That is, you press the shutter release once to lock exposure and focus, and to swing the mirror out of the way. Your viewfinder goes blank (of course, the mirror's blocking it). Press the shutter release a second time to actually take the picture. Because the goal of mirror lockup is to produce the sharpest picture possible, and because of the viewfinder blackout, you can see that the camera should be mounted on a tripod prior to taking the picture, and, to avoid accidentally shaking the camera yourself, using an off-camera shutter release mechanism is a good idea.

■ 0: Disable. Mirror lockup is not possible.

■ 1: Enable. Mirror lockup is activated and will be used for every shot until disabled.

Canon lists some important warnings and techniques related to using mirror lockup in the Rebel T2i manual, and I want to emphasize them here and add a few of my own, even if it means a bit of duplication. Better safe than sorry!

■ Don't use ML for sensor cleaning. Though locked up, the mirror will flip down again automatically after 30 seconds, which you don't want to happen while you're poking around the sensor with a brush, swab, or air jet. There's a separate menu item—sensor cleaning—for sensor housekeeping. You can find more about this topic in Chapter 9.

■ Avoid long exposure to extra-bright scenes. The shutter curtain, normally shielded from incoming light by the mirror, is fully exposed to the light being focused on the focal plane by the lens mounted on the T2i. When the mirror is locked up, you certainly don't want to point the camera at the sun, and even beach or snow scenes may be unsafe if the shutter curtain is exposed to their illumination for long periods. (This advice also applies to Live View, of course, because the sensor is similarly exposed while you're previewing the image on the LCD.)

■ ML can't be used in continuous shooting modes. The Rebel T2i will use single shooting mode for mirror lockup exposures, regardless of the sequence mode you've selected.

■ Use self-timer to eliminate second button press. If you've activated the self-timer, the mirror will flip up when you press the shutter button down all the way, and then the picture will be taken two seconds later. This technique can help reduce camera shake further if you don't have a remote release available and have to use a finger to press the shutter button. You can also use the Remote Controller RC-5 or RC-6. With the RC-5, press the transmit button to lock up the mirror; the shot will be taken automatically two seconds later. With the RC-6, set the remote for a two-second delay to produce the same effect.

C.Fn IV-09: What Happens When You Partially Depress the Shutter Release/Press the AE Lock Button

Shutter button/AE lock button (*). This setting controls the behavior of the shutter release and the AE lock button (*) when you are using Creative Zone exposure modes. With Basic Zone modes, the Rebel T2i always behaves as if it has been set to Option 0, described below. Options 1, 2, and 3 are designed to work with AI Servo mode, which locks focus as it is activated, but refocuses if the subject begins to move. The options allow you to control exactly when focus and exposure are locked when using AI Servo mode.

In the option list, the first action in the pair represents what happens when you press the shutter release; the second action says what happens when the AE lock button is pressed.

■ 0: AF/AE lock. With this option, pressing the shutter release halfway locks in focus; pressing the * button locks exposure. Use this when you want to control each of these actions separately.

■ 1: AE lock/AF. Pressing the shutter release halfway locks exposure; pressing the * button locks autofocus. This setting swaps the action of the two buttons compared to the default 0 option.

■ 2: AF/AF lock, no AE lock. Pressing the AE lock button interrupts the autofocus and locks focus in AI Servo mode. Exposure is not locked at all until the actual moment of exposure when you press the shutter release all the way. This mode is handy when moving objects may pass in front of the camera (say, a tight end crosses your field of view as you focus on the quarterback) and you want to be able to avoid change of focus. Note that you can't lock in exposure using this option.

■ 3: AE/AF, no AE lock. Pressing the shutter release halfway locks in autofocus, except in AI Servo mode, in which you can use the * button to start or stop autofocus. Exposure is always determined at the moment the picture is taken, and cannot be locked.

C.Fn IV-10: Using the Set Button as a Function Key

Assign Set button. You already know that the Set button is used to select a choice or option when navigating the menus. However, when you're taking photos, it has no function at all. You can easily remedy that with this setting. This setting allows you to assign one of five different actions to the Set key. Because the button is within easy reach of your right thumb, that makes it quite convenient for accessing a frequently used function. When this Custom Function is set to 5, the Set button has no additional function during shooting mode (except to activate Live View when it is turned on), and options 0 through 4 assign an action to the button during shooting.

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