Demonstration of Aperture and Focal Length

Row of beer bottles, show with a narrow DOF to highlight a single bottle of Killian's
The simplest things you can control on a camera are aperture, shutter speed and ISO (film) speed. Unless you are really trying to create a special look, you probably want to keep the ISO setting as low as possible to cut down on noise, so that leaves shutter speed and aperture. If you have a zoom lens (or two), you also get another lever to control: the focal length of the image. Here are two photo sets I built to help me visualize how the different settings will contribute to the final image. Use the prev and next controls to jump to the next setting, or press play to see a slideshow of the entire range of settings for the control.

Note: Thanks to Patrick Fitzgerald for creating the handy Slideshow Wizard, which is what I used to create these examples!

Varying Aperture
For this example, I kept the camera at a fixed focal length, focus and ISO setting, and used the aperture priority mode to automatically select the shutter speed. This shows how the aperture setting can be used to control the depth of field. The major trade-off is that the smaller aperture lets through less light, which means that the shutter speed has to be longer to achieve the same exposure. This is fine for shooting a static shot like this one, but would not work for moving targets. In those cases, you will need to increase the ISO speed (which makes the picture noisier), or add light (which is a whole different subject).

Varying Focal Depth
For this example, I varied the focal depth by varying the zoom lens (and switching lenses to cover the full range), and kept the subject size constant by moving my camera closer to the subject. The effect is to vary the separation between objects at different distances from each other. With a large focal length, the depth of everything appears compressed, and objects seem closer together. Conversely, with a short focal length, foreground objects appear much larger then background objects. This can be cool for making bobble headed cat pictures, or creating funny relations between subjects in a picture.

Equipment used: Nikon D40, Nikon 50mm f/1.8, Nikon 18-55mm f/3.5-5.6, Nikon 55-200mm f/4.5-5.6

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5 Responses to Demonstration of Aperture and Focal Length

  1. Alex says:

    Wow! This is cool!
    So in the second one, you moved the camera and not the globe or kappa?

  2. mahto says:

    Thanks! Yeah, just the camera. Thats why it’s important to move around to frame a shot, even if you are using a zoom lens.

  3. Lee says:

    Great to see that you got this posted and found a package to do the slide show sequencing. I didn’t realize the flattening effect of the long zoom was so dramatic. I will have to think more about this when framing things in the future.

  4. I think the variation of focal length to get the same shot is the most difficult to master. Shutter and aperture have very obvious effects. To visualize the difference focal length will make is much more difficult. Next lens on my list of fun will be a wide angle one, the 10-22mm from Canon most likely. Wide angle allows for some very interesting effects, but they’re expensive and I’m pretty sure don’t come into usefulness all that often.

  5. mahto says:

    @Lee: Yeah, it’s an interesting dimension, and like Matt says, fairly difficult to master. I’ve been trying to practice by checking how things change at the ends of the camera lens that I have. I suppose studying some movies might help to, to see how they use it for dramatic effect.

    @Matt: The only thing i’ve found so far is to just do the legwork and see how different focal lengths work. Or, just use a fixed-length lens so I don’t have any options… A wide angle lens sounds fun, have you considered renting one? I went the other way and got a macro lens, but lucked out and found one on craigslist.

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