Focus on Landscapes

So today is a first here on the Shutteresque blog, where we take a question from the audience! My friend Jon asked me, “If you’re trying to take a picture of a cityscape, how do you pick a focal point?”

When you are shooting with a point-and-shoot camera, there’s probably not much you can do other than try to pick the most distinctive/unique building, or some other element of the scene which stands out and deserves to be the center of attention. The easiest way is to find what draws your eye naturally once you’ve composed a shot, and focus on that. Generally that will be the element that draws the viewer’s eye as well, so having it in focus is an easy choice. But you can get creative; sometimes I like to leave the entire cityscape ever-so-slightly blurred, and focus on a tree nearer to me.

If you’re shooting with a camera with manual controls — and this does include some ‘point and shoots,’ I note — you have a few more options beyond just picking a focal point and taking what the camera gives you. But to really make use of those options you need a bit of understanding of precisely how a photographic image is exposed.

Onwards to the quick summary/refresher course!

‘Exposure’ is made up of three parts: duration (shutter), sensitivity (ISO) and depth-of-field (aperture). I’ll give a quick run-down of these three, and then focus on how one of them answers Jon’s question to some degree.

  • Shutter speed controls how long the film (or digital sensor) is exposed for. This is pretty straightforward; a longer exposure lets in more light, but also has a chance of less fine detail if things move. Using a longer exposure is called ‘dragging’ the shutter. (If you’ve ever heard the term ‘shutter drag’ and been confused, now you know!) Shutter speed is measured in seconds, or fractions thereof.
  • ISO used to be the sensitivity of film, and now also refers to the sensitivity a digital sensor operates at. ‘ISO’ here is an abbreviation for three different ISO standards, defining how sensitive different types of photographic negative had to be. The actual origins of the ISO numbers are mathematically complex, but the short form here is that the lower the number, the more light is required to effect the emulsion (or the digital equivalent thereof). ISO 200 requires half the light of ISO 100 to get the same exposure, and so on. Think of this as like the brightness on a monitor, only in reverse… the higher it’s turned up, the brighter the image will be (if all other elements remain the same).

    Of course, there’s always a tradeoff. On film, you would see speckled patterns throughout images, known as ‘film grain.’ The higher-sensitivity films would have more pronounced grain, and the same is true of noise on digital sensors. Unfortunately, where film grain was sometimes aesthetically pleasing (to the point that plugins exist to replicate specific grain patterns in digital images), digital noise often is less so, though — just as with film (where an Ilford Delta negative would have a different grain pattern than Kodak TMAX negative) — different camera sensors have different noise levels and patterns.

  • Aperture is the most interesting of the three, and the one that concerns us here. Nearly every lens has a bladed aperture inside of it, which controls how light reaches the sensor. The wider the aperture is, the more light gets through. The smaller the aperture, the less. People will sometimes refer to this as the lens speed, since a lens with a wide maximum aperture will be able to let more light in at once and thus get an exposure in a shorter time. Think of it like the iris in your eyeball; the wider it is, the more light gets in.

    However, as with everything in photography, there is a catch. Due to optical physics, the aperture size also changes HOW things are exposed. A wide aperture will give you a shallow depth of field; photographers use this technique to keep a foreground in focus and a background blurred. A small aperture will give you a wide depth of field, keeping most of the image in focus. Aperture is measured in f-numbers, with the aperture decreasing in size as the number increases; the photographic group Ansel Adams helped found is known as f/64 because they took very sharp images with small apertures. Wikipedia has an excellent article on F-numbers and F-stops.

Of these, aperture is in many ways the trickiest of the three elements to master, but — as that affects focus directly — this is the one that concerns us in answering Jon’s question.

Focusing on a single element — such as a building — is hardly rocket science. Today’s cameras have autofocus that can handle much of the task, and many cameras (including the 5D Mark II that I shoot with) support a live view where you can zoom in on what the lens is seeing and adjust the focus to minute levels. So focusing on a single building is not difficult. The problem in shooting a cityscape is, of course, that the buildings are at different distances from you, so in many cases focusing on a single building could leave another out of focus. But a cityscape is often most dramatic when the buildings are in crisp focus across the entirety of the scene.

Looking at the list above, the trick is simply to use a smaller aperture. By increasing the F-number (making the aperture smaller), you will increase your depth-of-field and be able to get the cityscape in sharper focus. Unfortunately, this also means you’ll be getting less light through. If you’re shooting handheld, your only option is to increase the ISO accordingly, making the camera more sensitive to the light you’re getting. If you’re shooting on a tripod, of course, you can keep the ISO low and just drag the shutter.

What the appropriate ISO is really depends on the situation. I tend to shoot f/14 for cityscapes around my neighborhood, or sometimes even wider, because I like to keep my exposures under thirty seconds. I find under thirty gives me less chance of someone wandering through with a flashlight, biking past with their little safety-blinkers and so on; I’ll sacrifice a little bit of sharpness for the sake of getting the shot before I freeze.

When further out, where I’m less likely to run into such things, I’ll increase my aperture as suits the shot. But it’s worth remembering that not all cityscapes do need /everything/ in sharp relief; I shot the following image at f/11.

Bridge by Night

The blur of the farther elements helps to actually make the bridge details stand out more, which was the effect I wanted in this image. So there is no ‘one true way.’

But if you find that you want the entire cityscape in focus and are not achieving it, the answer is to dial up the F-number and compensate your exposure accordingly. Hopefully, this (somewhat long-winded) post answered your question, Jon! 🙂


~ by Rachel on February 28, 2009.

One Response to “Focus on Landscapes”

  1. Yes! (A long-winded answer deserves a short reply.)

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