We already know that depth of field is how much of your picture is in focus. In particular, it’s what distances from your lens are in focus. Is it a narrow range? A wide one?
Here are a few sample images that show you how depth of field actually works. I took these very carefully– I placed the camera on a tripod, and focused at exactly the 12-inch mark on the ruler. I made sure to keep everything lined up as carefully as possible, and then took shots at f/4, f/8, f/16, and f/32. Most lenses don’t go down to f/32, but this one did so it was good for shooting these sample photos:
At f/4, pretty much the only thing that’s in focus is the 12-inch mark itself– you can’t even read any of the other numbers. At f/8, you can start to see the numbers 11 and 13 come into focus, though they’re still a little soft. At f/16 the numbers 10-14 are pretty clear, and you can actually make out other numbers. At f/32 you can read the entire visible length of the tape measure, and the majority of it is fairly sharp.
I recommend clicking through on the above images and studying the larger images, since they give you a pretty good idea of how the depth of field breaks down as a percentage of the image. If you have a Flickr account, you can click the “all sizes” link above the photos to see them in their original eight-megapixel glory.
The astute reader will notice that these are the same images that are at the top of every page on this blog. I originally took them to use as examples when I was teaching Stop Shooting Auto! as a class for my coworkers, and I instantly loved them. They seemed to produce an aha! moment for everyone who saw them.
Let’s go back to our six-year-old’s landcscape for a bit. I’ve added something to the illustration this time– an indicator of what percentage of the image would probably be in focus at various apertures. The places where there’s a straight yellow line are the areas that will probably be in focus, and the angled lines indicate what will be out of focus– it’ll be just a little bit soft close to the solid yellow line, and stuff far away will be very blurry. Note that I guessed at these based on my experience rather than using any super-magical scientific math wizardry to figure it out. Treat them as rough guidelines rather than hard scientific fact.
Here’s how it might look at f/4:
and at f/8:
and finally, at f/16:
Clearly, if we want our image to be in focus across pretty much the whole range, we should use f/16 or smaller. If we want to blur most of the image, we should use a large aperture like f/4.
How am I doing? Is aperture less scary now? Does it sort of make sense?
Next lesson: Exercise: Depth of Field
Stop Shooting Auto! 
You rock! I am learning so much!!! My 40D is shipping today! My first DSLR – and one I hope will last SEVERAL years. Could you address hyper focal?
Thanks again, Susan D
Congrats on the new purchase! The 40D is an excellent camera.
I will add hyperfocal distance to my list of things to write.
purchased a canon 400D couple of days back. since than I am searching the links to help a new bie like me.
could find this link yesterday evening. and will say, its one of the best series of articles i have seen so far.
in such a simple language and with illustration provided, this series is really great.
you Rock !!
Thanks a TON !
I just want to say thanks for all the thought and hard work you must have put into doing this for all of us out here in wnat to learn land. As for me it has helped me tremendously in only a few nights of reading. I will continue to with your lessons to the end. Thank You very much, Jeff T.
I’ve always been a fan of DOF but it’s often a hit and miss thing for me.
I can’t thank you enough ^___^
Many years ago in a junior college photography course the instructor had us all do a simple exercise that cemented the depth of field concept for me. He told the entire class (sitting some distance from him) to hold one hand out at arms length with the “thumbs up” sign, hold the other hand up to one eye with fingers curled to form a tube you can look through (other eye is closed), and finally to move that thumb at arms length so the thumb was positioned next to him while looking through the tube. He said, “Either I’m in focus or your thumb is in focus, right? You can’t get both in focus while looking through that large tube can you? That’s f/4.” Then he said, “Close your fingers down so you’re looking through a very small opening. Both your thumb and I are now in focus. That’s f/32.” Try this out on a distant tree or something and see how it works.
Thank you soo much for sharing this! I’ve been struggling to understand depth of field and you’ve made it soo much easier! Many, many thanks!
Your site is excellent! I just got a Nikon D5000 and can’t put it down. Regarding depth of field…I have a question. What is the object in your example that is the primary focus? Is it the tree? What if I focused on the flower and used the same f/16? Would I get the same result?
That is a surprisingly excellent question, and the truth is that I didn’t specifically pick a focus point when I created those illustrations. Bad Patti, bad! Can I claim that I was too busy focusing on my sophisticated artistic skills? Hrmm, probably not.
Here’s the deal. Generally when you focus on something, one third of your depth of field will be in front of the subject, and two thirds will be behind it. If you focused on the flower then no, you wouldn’t get the same effect. More of the area in front of the flower would be in focus (though none of it might actually be in your image) and the mountains in the back would not be sharp.
This site is absolutely priceless!! I have learned so much so far! I am truly thankful to you for takin the time to put all of this info in one place, and presenting it in such a fun and advantageous way! I just bought my new Canon and I was absolutley dumbfounded when I read the manual. You have beaten back that fear and unleashed a powerful lust to learn and adapt. Thank you so much!!