Custom Function specifics

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In this section, I explain each of the Custom Functions and the options that you can set. As you read about each Custom Function, consider how you could use it to simplify or customize the camera. You don't have to set each option, and it is likely you may find only a few that are useful to you in the beginning. But as you continue shooting, you'll likely grow to appreciate the power that they offer.

Keep in mind that the functions are easy to find, so you can go back and reset them if you don't like the changes that you've made. I think that you will be pleasantly surprised at how much more you'll enjoy the XSi/450D after you customize it for your shooting needs.

C.Fn I: Exposure

In this group, the two Custom Functions enable you to determine the amount of fine control you have over exposure and over flash exposure synchronization speeds when you're shooting in Aperture-priority (Av) mode.

Table 5.1

Custom Functions

C.Fn Number

Function Name

Group I: Exposure


Exposure-level increments


Flash synchronization speed in Av mode

Group II: Image

3 Long-exposure noise reduction

4 High ISO speed noise reduction

5 Highlight tone priority

6 Auto Lighting Optimizer

Group II: Image

3 Long-exposure noise reduction

4 High ISO speed noise reduction

5 Highlight tone priority

6 Auto Lighting Optimizer

Group III: Autofocus/Drive


AF-assist beam firing


AF during Live View shooting


Mirror Lockup

Group IV: Operation/Others

10 Shutter button/AE lock button

11 SET button when shooting

12 LCD display when power ON

13 Add original decision data

Group IV: Operation/Others

10 Shutter button/AE lock button

11 SET button when shooting

12 LCD display when power ON

13 Add original decision data

C.Fn-1: Exposure-level increments

The options available for this function enable you to set the exposure increment to use for shutter speed, aperture, exposure compensation, and Auto Exposure Bracketing (AEB). The exposure increment you choose is displayed in the viewfinder and on the LCD as double marks at the bottom of the exposure-level indicator. Your choice depends on how fine of a control level you want. Here are the C.Fn-1 options with a description of each one:

0: 1/3-stop. This is the Rebel XSi/450D's default option, and it offers the finest level of exposure control. Using this option, the camera displays shutter speeds in finer increments such as 1/60, 1/80, 1/100, 1/125 second, and so on. And it offers apertures as f/4, f/4.5, f/5, f/5.6, f/6.3, f/7.1, and so on.

♦ 1: 1/2-stop. This is a coarser exposure control setting. Using this option, the XSi/450D displays shutter speeds in increments such as 1/60, 1/90, 1/125, 1/180 second, and so on. And it offers apertures as f/4, f/4.5, f/5.6, f/6.7, f/8, f/9.5, and so on. You may want to set this option when you want to quickly make larger changes in exposure settings with a minimum of adjustments.

C.Fn-2: Flash sync. speed in Av (Aperture-priority AE) mode

This function enables you to either have the flash sync speed set automatically or sets it to a fixed 1/200 second in Av mode. Here are the options and a description of each one:

♦ 0: Auto. When you're shooting in Av mode, choosing this option means that the XSi/450D will choose a shutter speed of 1/200 second, the flash sync speed, or slower. Slower flash sync speeds allow the scene to be illuminated by both the flash and the ambient light in the scene. However, you must watch the shutter speed because at slow shutter speeds, any subject or camera movement appears as a blur. As long as the shutter speed is reasonably fast, this option is nice because the combination of ambient light and flash creates a much more natural-looking image than using the next option.

♦ 1: 1/200 sec. (fixed). With this option, the flash sync speed is always set to 1/200 second and the flash provides the main illumination with less ambient light being included in the exposure. While this option prevents blur from subject or camera movement that you may get using option 0: Auto, you'll likely get flash shadows and a dark background that are characteristic of flash images with this option.

C.Fn II: Image

The Image Custom Function group concentrates primarily on avoiding and reducing digital noise (a grainy and mottled appearance in the image), allowing you greater latitude in avoiding blown highlights, or highlights that are completely white with no detail, and improving the appearance of dark and low-contrast images.

Reference For details on digital noise, see Chapter 6.

C.Fn3: Long-exposure noise reduction

With this function, you can turn noise reduction on, off, or to set it to automatic for long exposures. If you turn on noise reduction, the reduction process takes the same amount of time as the original exposure. In other words, if the original image exposure is 1 second, then noise reduction takes an additional 1 second. This means that you cannot take another picture until the noise reduction process finishes, and, of course, this greatly reduces the maximum shooting rate in Continuous drive mode. I keep the XSi/450D set to Option 1 to automatically perform noise reduction if it is detected in long exposures. Here are the options and a description of each one:

♦ 0: Off. This is the default setting where no noise reduction is performed on long exposures. This maximizes fine detail in the image, but it also increases the chances of noise in images of 1 second and longer. With this option, there is no reduction in the maximum burst rate in Continuous drive mode.

♦ 1: Auto. The camera automatically applies noise reduction on 1 second and longer exposures if it finds noise present. If the Rebel XSi/ 450D detects noise that is typically found in long exposures, then it takes a second picture at the same exposure time as the original image, and it uses the second image, called a "dark frame," to subtract noise from the first image. Although technically two images are taken, only one image — the original exposure — is stored on the Secure Digital (SD/SDHC) card.

♦ 2: On. The Rebel automatically performs noise reduction whether or not it detects noise on all exposures of 1 second and longer. This option slows shooting down considerably because the Rebel XSi/450D always makes the dark frame to subtract noise from the original image, and the dark frame is exposed at the same amount of time as the first image. Weigh the option you choose based on the shooting situation. If you need to shoot without delay, then option 0 or 1 is preferable. But if you want to save time at the computer applying noise reduction during image editing, then option 2 is the ticket.


Because Canon has a good noise reduction algorithm, this setting maintains fine detail in images, and reducing shadow noise is advantageous. But it pays to check your images to ensure that a watercolor-type effect from noise reduction isn't objectionable. Note also that the options tend to be all or nothing. If you turn on High ISO speed noise reduction, it's applied at all ISO speed settings. Here are the options and a description of each one:

♦ 0: Off. No noise reduction is applied to high ISO images.

♦ 1: On. The XSi/450D applies noise reduction to all images, particularly high ISO images. At low ISO speed, this option is useful for further reducing noise present in shadow areas of the image. The maximum burst speed is reduced using this option.


If you have C.Fn-4 set to On, you cannot use White Balance Bracketing.

If you're using Live View and you have Option 2 set, then no image displays on the LCD during the time that the camera performs the dark-frame noise-reduction exposure.

C.Fn-4: High ISO speed noise reduction

This option applies more aggressive noise reduction to shadow areas in particular when you're shooting at high ISO speed settings. (The camera applies some noise reduction to all images.) If you turn this option on, noise in low-ISO images is further reduced.

C.Fn-5: Highlight tone priority

One of the most interesting and useful functions is Highlight tone priority, which helps ensure good detail in bright areas such as those on a bride's gown. With the function turned on, the high range of the camera's dynamic range (the range between deep shadows and highlights in a scene as measured in f-stops) is extended from 18 percent gray (middle gray) to the brightest highlights. Also, the gradation from middle gray tones to highlights is smoother with this option turned on. The downside of enabling this option is increased digital noise in shadow areas. But if you're shooting weddings or any other scene where it's critical to retain highlight detail, then the tradeoff is worthwhile. If noise in the shadow areas is objectionable, you can apply noise reduction in an image-editing program.

However, if you turn on Highlight Tone Priority, ISO speed settings are reduced to 200 to 1600 (rather than 100 to 1600). The ISO display in the viewfinder, on the LCD panel, and in the Shooting information display uses a smaller character to indicate that this Custom Function is in effect. For example, instead of 200, the ISO appears as 2oo. Here are the options and a description of each one:

♦ 0: Disable. Highlight tone priority is not used and the full range of ISO settings is available.

♦ 1: Enable. The XSi/450D emphasizes preserving the highlight tonal values in the image and improving the gradation of tones from middle gray to the brightest highlight. Shadows go dark quicker and tend to show more digital noise. Also the ISO range is 200 to 1600 rather than 100 to 1600.

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