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Old Sep 23, 2008, 10:55 AM   #2
JimC
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Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
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Welcome to the forums.

You want greater depth of field (how much of the image is in focus as you get further away from your focus point). See this handy online Depth of
field calculator for a better understanding of how focal length, focus distance and aperture impact DOF (Depth of Field).

http://www.dofmaster.com/dofjs.html

You'll want to take a shot of your subject where you're capturing a wider angle of view with the main subject occupying a smaller percentage of the frame (versus a tighter head and shoulders shot) to maximize depth of field for a given aperture. You can also use a smaller aperture (represented by a higher f/stop number) to get more depth of field (although you will have limitations). Simply shoot in Av (Aperture Priority) mode and select a higher f/stop number, letting the camera pick the best shutter speed to use.

But, keep in mind that if you use a smaller aperture (higher f/stop number), you will get slower shutter speeds (which can allow blur from subject movement or camera shake if they get too slow). So, be aware of your shutter speeds when using smaller apertures, as you may need to increase your ISO speed (which is how sensitive the sensor is to light) to keep shutter speeds as fast as desired (and increasing ISO speed increases noise). See this handy online exposure calculator to get a better idea of how your aperture impacts the shutter speed you need for proper exposure:

http://www.robert-barrett.com/photo/...alculator.html

Also, be aware that if you go too small (for example, much over around f/11 or f/14, depending on the lens), you will start seeing softer images with some lenses due to diffraction, so you'll want to avoid aperture extremes. Most lenses are sharpest with their apertures set to around 2 or 3 stops down from wide open.

So, you'll want to balance the need for greater depth of field against the need for the sharpest subject, and you'll also want to consider how slower shutter speeds may impact your images when making decisions about what aperture to use, increasing ISO speed as needed to help prevent blur if you're not using a flash or tripod, depending on the lighting.

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