When making a decision about what aperture to use, a photographer has guidelines that can be followed. Based on the subject and composition, here are some simple suggestions.
Single theme or isolation composition: Sharpness is deliberately limited to the subject or area that is the focus of the image, leaving all other objects, both in front and behind, out-of-focus.
A telephoto lens is often a good choice for this type of shot, with a large lens opening (small f-number) such as f/2.8, f/4 or f/5.6. The subject is singled out from an otherwise busy scene. The blurry background and/or foreground can call further attention to the in-focus subject. This is a “visual law” referred to as visual weight: whatever is in focus is understood by the eye and brain to be of greatest importance.
Notice the gravel in front of the subject is out of focus as well as the
ground behind-Depth of Field affects before and after the subject.
Photos by Karen S. Craig
“Who cares” Apertures: When everything in the frame is of equal importance, at the same focused distance, the aperture used is not that much of a concern. Photographer Bryan Peterson calls this “who cares” aperture. If you are shooting a pile of leaves on the ground, a bouquet of flowers from above, anything on a white background, the aperture will not be used to create depth in the image.
Since there is writing in this photo, it needs to
be as sharp as possible, so f/11 would be the
best choice. Photos by Karen S. Craig
In these situations you would choose critical aperture. That is, whichever aperture yields the best sharpness and contrast. These would be apertures from f/8 to f/11.
Landscape or Distance apertures: To convey distance you need everything from front to back to be sharp.
Photo by Karen S. Craig
A wide angle on your lens and a stopped down aperture (large f-number, smallest lens opening possible) such as f/22 or f/32 will usually do the deed.
So next time you are setting up a shot, visualize what you want the final photo to look like and ask yourself these basic questions:
- What is my subject?
- Where do I want the subject to appear in the photo?
- How do I want the background to look?
Once you have these issues resolved, the question of what aperture to use should be easily answered and your image will be “in the can”. Here’s to those “perfect exposures”!
For more info: Check out this article at About.com
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