I shot these two photos of a dahlia to illustrate the impact of aperture on depth of field. The photo immediately below, with a large aperture of f/4, has minimal depth of field, while the photo far below with a small aperture of f/32 has much more depth of field.
The flower is in focus in both photos. In the low depth-of-field image (immediately below) the background is out of focus, and therefore visually separated from the foreground.
In this situation, the low depth-of-field image is preferrable (at least in my opinion). An important point with low depth-of-field photos: since most of the photo will be out-of-focus, try to maximize the focus you do have by placing the camera as parallel as possible to the primary subject of the photo.
[Both photos: 105mm f/2.8 macro lens, 157.5mm in 35mm terms, ISO 100, tripod mounted. Above 1/1250 of a second at f/4, below 1/20 of a second at f/32.]
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Jade: the problem is one of notation. The smaller the hole in the lens (also called the aperture) the more depth of field you have. The bigger the number, the smaller the aperture, so f/32 is short for an aperture that is way smaller (and has tons more depth of field) than f/4.
If all this sounds confusing, it really isn't so bad. I explain it carefully in my new book "Practical Artistry: Light & Exposure for Digital Photographers".
Best wishes - Harold
I was wondering how comes the top photo that has a larger aperture has a lower d.o.f as I would of thought a small aperture would lhave a lower d.o.f. I would appreciate the response.
I can't say for sure what the difference in macro mode might be for your particular camera, but in my experience the macro mode automatically zooms the camera to the maximum focal length. This will help make a shallower depth of field when taking photos of flowers and such. If you take the same photo but move closer and use a shorter focal length, then the depth of field will increase and you will see less isolation of the subject (given a fixed aperture).
In general, the tiny ccd sensors in modern point and shoot digital cameras make it difficult to get shallow depth of field. The advantage is that most everything will be in focus! Do a little googling around and you'll find some explanations of the relationship between the size of the sensor/film and depth of field.
Even though my digicam can go down to f2.8 in aperture-priority mode, the only way I'm able to get that wonderful shallow depth-of-field is by invoking the macro mode. This is a midrange Kodak DX7440, not a pro camera, but why would that be? In two test shots I made, the shutter speed and aperture were identical, but the focal point shifted.