In Chapter 9, you got a glimpse of the T1i's custom functions when I discussed mirror lockup. Custom functions are special commands that you access through the Custom Functions command on the third tool menu. Although a few of these commands, such as Mirror Lockup, seem more like primary commands that should be in the normal menu system, the bulk of the custom functions are commands that let you tweak and alter the behavior of other commands.
To alter a custom function, choose custom function (C. Fn) from the third tool menu. Use the left and right arrows to select the function you want to edit, and then click Set. You can then use the up and down arrows to change the value of that function. Press Set when you've configured it as you want it. Here's what they do:
01 Exposure Level Increments This lets you change the increment used by exposure compensation, flash exposure compensation, and autoexposure bracketing. You can choose between a 1/3 stop (the default) or a 1/2 stop. Obviously, a 1/3 stop gives you a finer degree of exposure control, but a 1/2 stop is easier for some people to conceptualize.
02 ISO Expansion Enables ISO 6400 and 12,800, as discussed in Chapter 7.
03 Flash Sync Speed in Av (Aperture-priority AE) mode The shutter in the Rebel T1i is composed of two curtains: one opens to expose the sensor, and the other closes to obscure the sensor. On very fast shutter speeds, the second shutter starts moving to close off the sensor before the first shutter has completely opened. In other words, the sensor is never fully uncovered. Instead, the shutter creates a moving slit that passes very quickly in front of the image sensor. If you fire a flash while this slit is moving across, you'll get a single vertical streak of flash exposure. In other words, you want to use the flash only with a shutter speed that completely uncovers the sensor. In addition, you want the flash in sync with the shutter so that it fires when the shutter is completely open.
By default, when shooting in Aperture Priority mode, the camera will choose any shutter speed from 30 seconds to 1/200th of a second. These are all speeds that will work with the flash, because they all allow the sensor to be completely revealed. However, these longer speeds also mean you run the risk of camera shake. If you want, you can change this custom function to limit the choice of shutter speeds from 1/200th to 1/60th of a second. This will properly expose your subject and reduce camera shake, but will possibly result in the background being too dark. You can also fix the shutter speed at 1/200th, which will also help prevent camera shake, though the background will be even darker.
04 Long Exposure Noise Reduction We looked at this function in our discussion of night shooting in Chapter 10.
05 High ISO Speed Noise Reduction We also looked at this function in our night shooting discussion.
06 Highlight Tone Priority If you're shooting a scene with lots of bright details—people in white clothing, street shots with white buildings, polar bears in bright sunlight—then activating Highlight Tone Priority can help preserve more details in your highlight areas. If you shoot raw, you can get this same functionality through highlight recovery in your raw conversion software. Highlight Tone Priority provides this same type of highlight protection for JPEG shooters.
07 Auto Lighting Optimizer By default, when you shoot JPEG images in darker, lower-contrast situations, the T1i automatically brightens them to restore better contrast. You can increase the amount of brightening or deactivate this feature altogether using this custom function. In very low light, this feature can add additional noise to your images, so you might consider turning it off, to see if you get cleaner results. If you're shooting raw, your raw files will be tagged with Auto Lighting Optimizer data. Canon's Digital Photo Professional will read this data and correct your image.
08 AF-assist beam firing This allows you to tell the camera to not use its built-in pop-up flash for autofocus assist. You can independently toggle the use of both the built-in flash and external flashes.
09 Mirror Lockup We discussed mirror lockup in our discussion of night shooting in Chapter 10.
10 Shutter/AE Lock button This function offers four choices that let you change the functionality of the Exposure Lock button (*). AF/AE Lock is the normal behavior that we've seen throughout this book. AE Lock/AF lets you lock exposure and focus separately, rather than having them both happen when you half-press the shutter button. With this option activated, pressing the Exposure Lock button (*) causes the camera to autofocus, whereas halfpressing the shutter causes the camera to meter and lock exposure. The other two options affect the function of the AI Servo feature. See page 188 of the T1i owner's manual for details.
11 Assign Set Button You can assign one of five features to the Set button on the back of the camera. This provides you with quick access to either the Quick Control screen, Image Quality, Flash Exposure Compensation, turning the LCD monitor on and off, or displaying the menu.
12 LCD Display When Power On By default, the camera always activates the rear-panel LCD display when the camera is powered up. If you prefer, you can choose Retain Power Off Status so the camera remembers the state of the LCD screen when you power it off. If you're trying to conserve battery power or if you're shooting in a location where the bright light of the LCD screen is inappropriate, this can be a great feature.
13 Add Original Decision Data If you activate this custom function, the camera will embed special information in your image. When used in conjunction with the optional Original Data Security Kit, it can be possible to determine whether an image has been altered.
DEFINITION: Image Forensics
Image forensics is the science of trying to determine whether an image has been altered. For photographs used in legal cases, knowing whether an image has been altered can be critical.
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Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.