Really, it's not that hard. Once you get the hang of it, it's actually fascinating to play around with, and can be used make your photos more beautiful. Think of "field" as the entire image you've shot--the subject and everything surrounding it. The "depth" is just that--how deep you see into the image. Do you see just the subject, and everything else is blurry? Or is everything in focus? That's depth of field.
Shallow depth of field = just the subject (or, even just a part of the subject)
Wide or deep depth of field = everything, or most everything, is in focus
There are times when it's effective to shoot with one, or the other, or somewhere in between. A lot of the time, it simply comes down to personal preference. Here are some macro shots I took of an Asiatic lily in my front yard; I took these specifically to experiment with DOF. For this series of images, I put my Canon 40D on the AP (Aperture Priority) setting. Um, wait--okay, the photos will be a little further down the page. :)
The reason I used the AP setting is because APERTURE determines DEPTH OF FIELD. The word aperture simply means opening, and refers to how open or closed the "hole" in your lens is. Here's the only tricky part to learn: The larger the aperture setting, the shallower the DOF is. The smaller the aperture, the greater the DOF is. Opposites. And opposites attract. :)
With the lenses in my camera bag, the smallest f-stop my Ellie can reach is f1.4, and the largest can go up to f32. Sometimes even a small change to this number produces dramatic results. By using the AP mode in the below images, I controlled the aperture, and I let my camera determine the shutter speed. That way, I focused entirely on the aperture setting without having to worry about anything else.
Okay, now here are my images. All the images are shot with ISO 100 for clarity, and I used a tripod and my camera's two-second timer to counter camera shake. (I didn't want to use my remote.)
I set the first shot at f2.8 (the largest aperture for my macro lens), and increased the aperture with each shot. Notice that when I increased the F-number, that the camera slowed the shutter speed. That's because as the F-number gets larger, the aperture gets smaller, and the shutter needs to stay open longer to let in the proper amount of light.
f2.8, 1/100 second
f4, 1/50 second
f6.3, 1/20 second
f9, 1/10 second
f11, 1/8 second
f16, 1/4 second
That's as high as I set the F-stop. The entire field is not yet sharp, but you get the idea. I like most of these images for different reasons. I love the f2.8 image because its DOF is so shallow, and I can see only the tips of the pistil and stamens (you'll have to look up flower terminology on your own). With the f6.3 image, I can see that the whole image is of a flower, but there's still a sense of depth to it--the shadowy base of the center is still a little out-of-focus and mysterious. I do like the f16 image, too, because there still is a sense of depth, but my eyes are free to explore down into the flower. I can see the yellow center more clearly, and I can catch more detail on the center parts of the petals.
My favorite? Probably the f6.3 or the f9 shot. There is a lot to explore in these images, with a lot of mystery, too.
I hope you learned a little something! I didn't necessarily post this to teach you, of course; it's just that when I demonstrate how to do something with my camera, then I learn it more thoroughly. Hence, this little lesson in DOF is really for me. But I also hope you enjoyed the lesson and my images. :)
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