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The Camera's Eye: How Cameras See

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The camera doesn't'see' the world the same way that the human eye does. Good photographers learn how their cameras 'see' and exploit this to create better images. An understanding of the differences between the way that a camera records light, and the way the brain interprets the information sent to it by our eyes, will help you create better photos. This ability to picture how a camera will record a scene is called visualization – a skill that all photographers need to practice.


Two dimensions not three

Our vision is stereoscopic. Humans have two eyes, and each looks at something from a slightly different angle. This enables us to judge distance and determine how close objects are to each other.

Stereoscopic cameras aside, cameras see through a single lens, and record the world in two dimensional images. We may not even realize this until it is pointed out; as we are accustomed to seeing two dimensional representations in the form of paintings, drawings and photographs.

Photographers don't have to worry about rendering depth too much as cameras take care of the business of accurately recording the scene in front of the lens. But we always need to be aware that the camera records an image with different characteristics than the one we perceive with our eyes.


Digital cameras have made the process of visualization much easier. All you need to do is to look at the image on the camera's LCD screen to see how it has been rendered in two dimensions. You can also use the camera's Live View feed to compose the image in the first place, rather than a viewfinder. These tools are useful because they help you visualize how your photos will look after you have processed them. And if something doesn't come out the way you planned, you have an opportunity to try again.


How our eyes work

Our eyes are constantly moving, taking in different aspects of the scene and adjusting instantly to changes in brightness. The brain takes this information and builds it up into a selective, moving image. How many times have you failed to notice something that is literally right in front of you? That's the result of your brain's selective vision.

Cameras are different. If the aperture is small enough, everything from the front to the back of the image is in focus and recorded in exquisite detail. You only have to enlarge an image taken with a modern digital camera on your computer to appreciate the resolution of modern cameras and optics.


Composition and backgrounds

Our eyes and brains are selective – when we look at something we tend to look at what interests us and ignore the rest. The camera records everything, so we need to find ways of guiding the viewer to look at whatever the photographer deems important. One way to do this is by being selective – close in on your subject and try to exclude anything that is a distraction.

If you're taking a portrait, for example, and someone is walking by in the background; that's a distraction. Your brain may ignore it when you're looking at the person you're photographing, but the camera will record it. Eliminating distractions helps simplify your composition and improve your photos.


I framed this flower carefully to avoid any distracting colours or bright highlights in the background. Using a short telephoto lens and a wide aperture setting helped me achieve this.


Selective focus

Selective focus is one of the easiest tools you have for guiding the viewer's eye to the important parts of your images. When we look at something our eyes adjust focus automatically, creating the impression that everything around us is in sharp focus. But your lens sees things differently – it can only focus on a single point within the frame. Whether the rest of the image is sharp or not depends on factors like the aperture, focal length and how close you are to the subject. By setting a wide aperture you can throw the background behind the subject out of focus; concentrating the viewer's attention on your subject (and also helping eliminate distractions).

This works best with prime lenses, as they typically have wider maximum apertures than zooms, although you can still use selective focus with zoom lenses to good effect. I wrote more on this technique in my article The Magic of Wide Apertures.


Here, I focused on the nearest monkey and set the aperture to f5.6 to blur the background. I didn't need to go all the way to f1.8, the maximum aperture of the lens, as I was fairly close to the subject and this results in less depth-of-field. Remember, when photographing a static subject like this, you can take several photos at different aperture settings and decide which is the best afterwards.

There are specialist lenses that exploit the concept of selective focus even further. Tilt-shift and perspective control lenses give you control over the positioning of the plane-of-focus. These lenses are expensive. If you're really interested in trying one out, renting is an option to see if you really like it. Lensbaby also makes a range of optics for SLR cameras that utilize selective focusing in creative ways.


The Canon EF TS-E 24mm f3.5L II tilt-shift lens.


Recording motion

Our eyes can't stop motion. Without cameras we would have no idea what a person looks like frozen in mid-movement. Cameras capture split-seconds of time and part of the appeal of photography is this glimpse into a world that we can't normally see.

Photographers have three options for recording motion. The first is to record the scene more or less as we see it, with a middling shutter speed of around 1/125 second. The result depends on the speed of the moving subject, but this usually produces a natural looking image.

The second option is to freeze time with a fast shutter speed. This captures motion in a way that we don't see it with the eye and is a technique used by sports and action photographers. You can use flash to achieve a similar effect in a darkened studio – the brief blip of light freezes the subject. This technique was pioneered by Harold Edgerton in the 1930's. He used it to take photos depicting, among other things, the impact of bullets on every day objects like fruit and playing cards.

The third option is to use a slow shutter speed to record motion as a blur. This is a common technique in landscape photography, where photographers often use low ISOs and narrow apertures in low light. In these conditions long shutter speeds are a necessity – my article How to Create a Beautiful Seascape in Thirty Seconds covers the technique in more depth.

You can also use slow shutter speeds to pan, or deliberately blur a scene while hand-holding the camera (this is called 'intentional camera movement' – Chris Friel creates beautiful images with this technique).


I took this photo with a shutter speed of 1/125 second. The motion of the water is more or less frozen.


I took this photo with a shutter speed of 1/2 second, with the camera mounted on a tripod. I asked my model to stay still so she remained sharp. The motion of the water is blurred, changing the mood of the image.


Perspective

Perspective is the apparent distance between objects. Our eyes see perspective in a certain way, and there is nothing that we can do to change this. Camera lenses, on the other hand, have their own perspective; which we can use creatively.

Wide-angle lenses exaggerate the distance between objects. If you look at a scene through a wide-angle lens, everything looks further away from you than it really is. Distance objects, such as trees or hills on the horizon, appear much smaller.

To get the best out of a wide-angle lens, you normally need to move in close to your subject so that it fills the frame. The advantage of wide-angles is that you can take photos that include lots of background. They are a useful lens for taking environmental portraits – a topic I wrote about in How to Capture Emotive Environmental Portraits.

Beware of ultra-wide angle lenses, as the extreme distortion and perspective are difficult to master. The idea focal lengths are between 24mm and 35mm on a full-frame or 35mm film camera. This equates to around 16-20mm on a digital SLR with a crop sensor. There are several popular zooms with focal lengths in the range of 10-20mm for crop-sensor digital SLRs; and if you own one it is wise to approach the 10mm end of the focal range with caution.


This photo, taken with a Sigma 10-20mm lens set to 10mm, has been spoiled by the distortion of the ultra-wide angle (look at the shape of the man's face). It would have been better to use a longer focal length.

Telephoto lenses, by contrast, compress perspective; they make objects appear closer together than they seem when viewed by the naked eye. This is something that you see in photos of sporting events, as photographers have to use super-telephoto lenses when they can't get close enough to the action to use shorter focal lengths. But you can use it for creative effect too. Photos of people often benefit from using a short telephoto lens to compress the perspective and bring the background closer.


I used a Sigma 50-150mm lens at 150mm to take this photo. The perspective of the telephoto lens has made the distant cliffs seem larger and much closer to the girl than they are in real life.


Conclusion

There are many ways in which cameras record light in a different manner to the ways in which our eyes and brains view the world. By learning how cameras 'see' you can take advantage of these characteristics to take better photos. This is part of visualization; and the difference between making a record of the subject and making an interpretation of it.

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