I’ll just say this up front – for a lot of people, this is really elementary stuff. Every photo class I’ve ever taken, for the first or second assignment, did something with DoF (depth of field). In any case, I was playing around and just happened to end up with some pictures that demonstrate it well, so I’m posting here. Someone said they liked this stuff before. We’ll see what you think.
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Gonna get really elementary on you for a second. Depth of Field is controlled by your aperture. The aperture is a hole that lets light reach your sensor or film. A big number means a tiny hole. A small number means a big hole. Lenses that are referred to as “fast” are lenses that are capable of really opening up the aperture wide, to let a lot of light in fast, which allows the “fast” capture of a picture, even in low light. My 100mm macro lens, which I took these pictures with, has an aperture (or f-stop) that goes up to f/2.8. Not bad.
Alright – got that out of the way. Here comes the DoF. The larger the aperture, the deeper the Depth of Field. Sometimes that is good. If you’re taking a picture of a few rows of people, you probably want them all in focus, right? Well I’m not taking pictures of lots of people – I’m taking pictures of a flower today. Isn’t it purdy? It’s the one African Violet that somehow I’ve never killed and my cats have never succeeded in eating. Furry leaves don’t go down so easy. Enough of that – picture stuff. Shallow DoF is useful more often than you’d think. If you take a look at that picture above, there is a nice flower, right? What there isn’t is much in the background. That’s because I used a really wide aperture (2.8) which blurs most everything else out. It doesn’t even keep the entire flower in focus, but I like the look, so good. Let’s try it with a smaller aperture:
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Here we are at 5.6. That’s 6 clicks down on this lens from 2.8 and gives us a little more DoF, as you can see. The flower is a bit more in-focus and the background is much clearer. This smaller aperture also means that you have a slower shutter speed to account for less light coming in. Keeping this lens still is pretty hard when you’re up close like this, so I’m using a monopod. It helps a bit. Six stops didn’t make that big of a difference, right? Let’s go all craz and crank the aperture WAY down:
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This is with an aperture of 32. That’s a LOT smaller than 5.6. 15 clicks. What is going on with the picture? Well obviously I was too lazy to get the tripod out and instead of 1/25th of a second (for the first picture) or 1/5th second (second picture), the exposure time here is 8 seconds. But it doesn’t matter right? Because the point wasn’t to frame this and put it on your wall – it was to look at the DoF. Clearly the camera is shaking a bit, but otherwise, the flower is entirely in focus. Look behind it. See that red candy bowl? That’s in focus too. Do you want to see the candy bowl? Well f/32 might be the aperture for you. If you were maybe more into looking at the flower, f/2.8 might be better. The point is, you can control this stuff. Not all lenses can go as low as f/2.8, but f/5.6 is very common, even on a pretty cheap lens, and that same lens can most likely do f/32 as well. In order to control for DoF like this, you’ll want to set your camera to Av or Aperture Priority mode. Some cameras even have a nifty DoF mode, but that’s between you and your hardware. In Av mode, you can select the aperture setting you like and the camera will pick the correct shutter speed to go with it. This is probably the second most common mode I use on my camera. Ooh… one last comment – DoF at any setting is deeper the further away you are from the lens. My flower above may be less than an inch deep, but since it was very close to the camera, it’s still not totally in focus close up. If I shot it sitting a few feet back at the same setting, it would all be in focus. Just something to think about.
Got any good DoF pictures of your own? Link to ’em below.