Aperture setting fstop

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aperture is one of three exposure settings, all explained fully in Chapter 5. Depth of field increases as you stop down the aperture (by choosing a higher f-stop number). For shallow depth of field, open the aperture (by choosing a lower f-stop number).

Figure 6-9 offers an example. Notice that the trees in the background are much more softly focused in the f/5.6 example than in the f/11 version. I snapped both images using the same focal length and camera-to-subject distance, so aperture is the only depth-of-field variable between the two images.

Of course, changing the aperture requires adjusting the shutter speed or ISO to maintain the equivalent exposure; for these images, I adjusted shutter speed only.

1 Lens focal length: In lay terms, focal length determines what the lens "sees." As you increase focal length, measured in millimeters, the angle of view narrows, objects appear larger in the frame, and — the important point for this discussion — depth of field decreases. Additionally, the spatial relationship of objects changes as you adjust focal length.

As an example, Figure 6-10 compares the same scene shot at focal lengths of 138mm and 255mm. I used the same aperture, f/22, for both examples.

Large depth of field

Large depth of field

Figure 6-8: A large depth of field keeps both near and far subjects in sharp focus.

f/5.6, 1/1000 second f/11, 1/200 second f/5.6, 1/1000 second f/11, 1/200 second

Figure 6-9: Raising the f-stop value increases depth of field.

Whether you have any focal length flexibility depends on your lens: If you have a zoom lens, you can adjust the focal length — just zoom in or out. (The Rebel XTi/400D kit lens, for example, offers a focal range of 18-55mm.) If you don't have a zoom lens, the focal length is fixed, so scratch this means of manipulating depth of field.

For more technical details about focal length and your camera, see the sidebar "Fun facts about focal length."

^ Camera-to-subject distance: As you move the lens closer to your subject, depth of field decreases. This assumes that you don't zoom in or out to reframe the picture, thereby changing the focal length. If you do, depth of field is affected by both the camera position and focal length.

Together, these three factors determine the maximum and minimum depth of field that you can achieve, as illustrated by my clever artwork in Figure 6-11 and summed up in the following list:

1 To produce the shallowest depth of field: Open the aperture as wide as possible (select the lowest f-stop number), zoom in to the maximum focal length of your lens, and get as close as possible to your subject.

1 To produce maximum depth of field: Stop down the aperture to the highest possible f-stop setting, zoom out to the shortest focal length your lens offers, and move farther from your subject.

Figure 6-10: Zooming to a longer focal length also reduces depth of field.

Figure 6-10: Zooming to a longer focal length also reduces depth of field.

Here are a few additional tips and tricks related to depth of field:

i When depth of field is a primary concern, try using aperture-priority autoexposure (Av). In this mode, detailed fully in Chapter 5, you set the f-stop, and the camera selects the appropriate shutter speed to produce a good exposure. The range of aperture settings you can access depends on your lens.

i Some of the fully automatic scene modes are also designed with depth of field in mind. Portrait and Close-Up modes produce shortened depth of field; Landscape mode produces a greater depth of field. You can't adjust aperture in these modes, however, so you're limited to the setting the camera chooses.

Greater depth of field:_

Select higher f-stop Decrease focal length (zoom out) Move farther from subject

Shorter depth of field:

Select lower f-stop Increase focal length (zoom in) Move closer to subject

Figure 6-11: Aperture, focal length, and your shooting distance determine depth of field.

l The Rebel XTi/400D also offers a special autoexposure mode called A-DEP, which stands for automatic depth of field. In this mode, the camera selects the aperture setting that it thinks will keep all objects in the frame within the zone of sharp focus. You can read more about this mode in the next section.

l Not sure which aperture setting you need to produce the depth of field you want? Good news: You camera offers depth-of-field preview, which enables you to see in advance how the aperture affects the focus zone. See the section labeled "Checking depth of field" for details on how to use this feature.

l The extent to which background focus shifts as you adjust depth of field also is affected by the distance between the subject and the background. For increased background blurring, move the subject farther in front of the background.

l If you adjust aperture to affect depth of field, be sure to always keep an eye on shutter speed as well. To maintain the same exposure, shutter speed must change in tandem with aperture, and you may encounter a situation where the shutter speed is too slow to permit hand-holding of the camera. Lenses that offer optical image stabilization do enable most people to handhold the camera at slower shutter speeds than non-stabilized lenses, but double-check your results just to be sure. (Note that if you use a tripod, most lens manufacturers recommend that you turn off the stabilization feature; check your manual to be sure.)

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  • Crispus
    How set fstop on digital rebel?
    8 years ago
  • Bertoldo
    How to adjst aperature with canon 400 d?
    2 years ago
  • Milen
    How can i get a blurry background uaing my canon 400D?
    2 years ago
  • heike seiler
    How to change aperature on canon rebel xti?
    1 year ago
  • irene
    How to change apiture on a cannon 400d?
    12 months ago
  • emmanuel
    How to adjust aperture on canon rebel xti?
    11 months ago
  • Janina
    How to Change apperture in 400d?
    9 months ago
  • Caradas
    How to set Aperture on canon 400d camera?
    8 months ago
    How to reduce aperature on a canon ef left?
    7 months ago
  • tiblets sheshy
    How to change focal length of canon 400d to 2.8?
    3 months ago
    What is aperature range on canon 400d?
    23 days ago
  • william stovall
    What is the lowest exposure setting rebel xti eos?
    19 days ago

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