ExpoImaging ExpoAperture2 Manual (Imperial/Standard) - Manual (Page 7)

ExpoAperture 2 Depth-of-Field Guide Manual
V 1.0
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aperture setting. For an f/2.8 lens this would be f/5.6 or f/8. Therefore, using a smaller
aperture, like f/16 or f/22 to improve depth-of-field may actually decrease sharpness in your
photos.
The most common reason for lack of sharpness in photographs is camera movement, or
what is commonly referred to as motion blur. You can usually assume that camera
movement reduced sharpness in a photograph when nothing in the image is in focus. If you
had a steady camera and did a reasonably good job of focusing, at least some part of the
photograph should be in focus.
To reduce camera movement, use a tripod. If you are unable to use a tripod, the faster your
shutter speed, the more likely you will be to avoid motion blur. As a rule of thumb, your
shutter speed should be set to at least one over the focal length of the lens you are using. For
example, if you are using 250mm lens, your shutter speed should be set to 1/250 of a
second. When possible, you should also brace yourself against a tree or wall to improve your
steadiness. For really large enlargements of your images, this may not be enough. When
handholding or using a tripod remember to press the shutter slowly, or even better, use a
cable release with your tripod. Use mirror lockup, if available, so the camera doesn't vibrate
when the mirror snaps up in order to take the picture. Following these guidelines should
result in tack sharp images.
If you are using a digital camera with a LCD viewing screen it will be nearly impossible to
tell if your picture is sharp or not by quickly looking at the LCD. Nearly everything on the
LCD appears in focus because of its small size. If you have a zoom feature that you can use
during playback, magnify the image as large as possible and then examine the areas that need
to be in critical focus to confirm they are as sharp as you want them to be.
Finally, the introduction of image editing software like Adobe Photoshop ® also changes
whether portions of a photograph, and the photograph as a whole, are more or less sharp to
the viewer. A complete discussion of the merits of post-processing sharpening are beyond
the scope of this manual. However, suffice it to say that, just as with all other aspects of
photography, there are numerous creative and quality benefits to be gained by capturing in
camera an image as close as possible to your intended print.
1.D - Permissible Circle-of-Confusion
In optics, a circle-of-confusion is a slightly out-of-focus point of light. A perfect lens when
focused on a point of light like a distant star would render it sharply on the image plane – as
a point of light. Since a lens can only render one plane in focus at a time, points of light that
are either closer or further away from the lens than our subject would be out-of focus.
Slightly out- of-focus, the points would appear as tiny circles. The permissible circle-of-
confusion is the largest that this circle can be and still appear to be sharp to the eye at a
normal viewing distance. Circles smaller than the permissible circle-of-confusion will always
appear sharp.
In order to determine the permissible circle-of-confusion we need to start with the final
product – the enlarged print. You may well ask, "Why start here?" The reason we are