Exercise: Depth of Field

(This shall forever be known as the too-many-yellow-rulers lesson. Sorry!)

f32Up ’til now, you’ve been just reading the exercises and maybe doing them in your head, but not getting the camera out and trying them yourself. It’s OK– I’m lazy too. This one is different though. You’ll want to get the camera and do the exercise. If you don’t, I’ll hunt you down and scowl at you.

In this exercise, you’ll get firsthand experience with how aperture affects depth of field. In order to do the exercise, you’ll need a large flat surface with some sort of measurements, or sharp regular pattern. Some things that would work well:

  • a tile floor with high-contrast lines
  • a striped or checkered blanket with high-contrast lines
  • a long tape measure

You’ll need about five feet of this patterned surface, and you’ll need to be able to get fairly close to it, so that you’re looking down the length of it. See the tape measure picture at the top for an example of what I mean. You’ll also need enough light to take a steady picture at f/16.

Set your camera to aperture priority mode, f/16, and manual focus. If you’re not in a very bright area, set your ISO to 1600, or as high as your camera will go.

Stand near your patterned surface so that you’re looking down the length of it. Pick a spot in the middle, and manually focus on it. Remember that spot, because you’ll be coming back to it. Once you have the image in focus, take a picture.

Without changing your position, change the aperture to f/8. Point your camera at the exact same spot, and take another picture. Do the same thing at f/4, and as wide as your lens will go.

f4f8f16

Pull the photos into your computer where you can examine them more closely, and you should have a set that looks something like the photos above. The photo taken at f/4 will have a narrow band in the center that’s in focus, and the rest will be blurry. The f/8 photo will have a wider focus area, and f/16 will be much wider.

For extra credit: repeat the exercise, but this time don’t take pictures. Instead, use the depth-of-field preview button on your camera to see what the shots would look like. Feel free to try out the apertures in between the ones I suggested too. You should see a much smoother transition of focus than at the widely-spaced apertures, of course.

The astute… OK, the barely-conscious reader will notice that the example photos in this exercise are also in the page header. I originally shot these as examples when I was teaching SSA! as a live class, and I wanted samples to hand out. I was happy when I saw the results. The students in the class seemed to grok depth of field as soon as they saw the images, and they had a field day duplicating them with their own cameras.

Now it’s time for you to go out and play. Put your camera in aperture priority mode, and wander around taking pictures. Create some blurry backgrounds and some crisp ones, just like you’ve always done, but this time do it on purpose. You have the power– use it.

Next lesson:  ISO: What is it?

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10 Comments

Filed under Aperture, Exercise

10 responses to “Exercise: Depth of Field

  1. Kelly

    Hi there,

    I am just reading this manual focus section and I don’t understand because I cant get mine to focus manually on anything near to me. You mentioned that it could be opposite but then you also mentioned an infinity symbol which I have looked everywhere and I don’t have! Is there something I am doing wrong?? My lens is a Canon 18-55mm 1:3.5-5.6 II

  2. stopshootingauto

    Kelly, what do you mean by “near to me”? All lenses have a minimum focusing distance, which means the closest object that they can focus on. For some lenses it’s really close (a few inches), and for some it’s several feet. I don’t remember what it is for the kit lens offhand, but it’s probably a couple of feet.

    You can figure out for yourself what the closest focusing distance is. Find something that’s, oh, about five feet away. Focus on it. Step a little bit closer, and then focus on it again. Keep moving closer until you can’t focus anymore, and then move back just enough that you can focus again. That will tell you what the closest focusing distance is for the lens you’re using.

    If I remember correctly, the Canon kit lens doesn’t have any distance indicators for focusing– just a ring on the front of the lens. You just have to do it by eye.

    By the way, your eye has a minimum focusing distance too. Hold your arm out straight in front of you and raise one finger, then close one eye and focus on your finger. Easy, right? Slowly move your finger closer to your eye and try to keep focusing on it. At some point, your finger will be so close to your eye that you just won’t be able to focus on it anymore.

  3. nicole

    extra credit question. i used the depth of field button and looked thru the viewfinder and all that changed was the it was darker at the higher f# and brighter at the lower f#. the depth of field didn’t change when i used the button. did i do something wrong? i did the picture part and it worked then.

  4. stopshootingauto

    nicole, what aperture were you using? I bet it did change, but sometimes it’s hard to see subtle changes in depth of field. You’ll see it most if you’re focusing on something close and at a sharp angle to the camera. Try looking down the length of a yardstick or a newspaper or something.

  5. This has been a greeat information source for me thank you so much! I feel I am at the max on my newbie camera (Canon Reble XTi) and need to get a more sophisticated camera now – scary thought :( but I am glad I am realizing the limitations, it shows I am learning something. DO you ahve any recommendatiosn for the next step camera?
    Thank you again for all of your invaluable information – it is fantastic.

  6. stopshootingauto

    Erin, that’s an excellent question. I’m going to answer it with another question, though– why do you feel limited by your camera? It’s hard to make a recommendation without knowing what problem you’re trying to solve.

    I may turn this question into a full-blown entry. It’s a good one.

  7. Well – I wish I had along list except that intuitively I feel I am not capturing the maximum in my photos. My ISO is limited -I would like more variety. The auto focus seems off at times as well. I would also like more flexibility with longer exposure times – my shutter speed is limited to 30 seconds without additional flash bulb, of course I need to look into the flash so that may be a moot point. :) I have had the Canon Reble XTi for almost two years now, it has been wonderful and maybe I am jumping the gun.

    My other concern is I have bene hired a few times now, and feel maybe I need to upgrade for a better sense of professionalism, even though I still qualify myself as an amateur. Thanks!

  8. stopshootingauto

    OK, you have something of a start there.

    I asked for two reasons. One is that coming up with concrete reasons helps you solidify the decision to buy a new camera, or not. The second is that the list you come up with is actually your shopping list– those are the features that you’re looking for in a new body.

    Extended ISO range is a good reason to upgrade, if you really need it and will use it. I’ve done that twice, once from the Rebel XT to the 5D, and again to the 5D Mark II.

    Autofocus “seeming off” is typically more a user function than a body function, in my experience. Using autofocus well is more work than just pointing and shooting. I’m not terribly good at it, but I’ve developed a good understanding of my limitations and that’s a good start.

    You can shoot more than 30 seconds with the XTi, though. The trick is to put the camera in bulb mode, and then use a remote of some sort. The burden of timing the shot is then on you rather than on the camera– you open the shutter, hold it open for as long as you want, and then close it. There are also remotes that have timers on them, though I’ve never used one. The nice thing about bulb mode is that precision isn’t terribly necessary– if you’re trying for a 90-second exposure and you miss it by ten seconds either way, it won’t change the exposure all that much.

    When I upgraded from the XT to the 5D, I had some very concrete reasons. One was high-ISO noise– I do a lot of low-light shooting, and the XT was much noisier than the 5D. Another was the postage-stamp viewfinder on the XT. I manual focus quite often, and I just wasn’t able to do so accurately with a teeny tiny viewfinder. There were a few other nice-to-haves in the 5D, but those two were the major motivators.

    It may seem like I’m trying to talk you out of a new body, but I’m not. I know that a lot of people buy new cameras for fairly nebulous reasons, with the misguided notion that a better camera will take better pictures, and that’s often not the case. Body upgrades can solve some problems, and they’ll sometimes give you the tools to solve others, but they’re never a panacea. I’d hate for you to spend a lot of money on a new body and be disappointed with the results.

    • Thank you for your insight – I feel I am taking great pictures actually of course with room for improvement always :) , I just am feeling a little limited I guess. Not sure if that makes sense. I am going to keep mine for a bit longer and play with the bulb function more. The ISO does irk me – but we shall see.

      Maybe I will keep this and skip the 5D and start playing with the 5D Mark II – just to see where I am at with things.

      Great blog I have forwarded to quite a few people – thanks!

      • stopshootingauto

        Both the 5D and the Mark II are excellent cameras, but I’m pretty sure that most everything in Canon’s line will take great photos. If you can borrow an upgraded body for a few days or even a few hours you can see how it feels to you and if it seems worthwhile to upgrade.

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