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Film - Digital

How does the focal length  of a lens affect perspective?

Different focal length lenses affect visual perspective in various ways. The focal length of the lens can also dictate where we place the camera in relationship to the the subject - we call this view point. With a wide angle lens we might need to move closer to the subject to fill the frame - while with a telephoto lens we might need to locate ourselves further back from the subject.

The effect of perspective relates to the principle of a vanishing point where the imaginary lines in an image meet at a single point in the distance.

Wide angle lenses tend to produce a visually distorted effect, making objects close to the lens seeming abnormally large while objects in the background become smaller. The wider angle of view the wide angle lens produces the more the distortion.

On the other hand, Telephoto lenses, tend to compress objects within the normal perception of perspective - the longer the focal length of the lens, the greater this effect becomes.

Move over image to view roll over image


In the diagram above we  can see why  this happens.  When an image of the scene is projected back to the film or CCD, with the 80mm lens,  the proportion of the film covered by the car, the thick yellow vertical line marked by the upper red and the upper blue diagonal lines)




This changes when we use the 20mm Lens.

While the proportion of the film covered by the top of the house, the thick red line marked by the green line and the top of the lamp post the lower red line decreases. 


As the focal length or power of the lens is increased the object being photographed begins to fill more and more of the frame. In the example above we can see that with a wide angle lens there is more space on each side of the plant while with the telephoto the space is reduced to a minimum.



Shot with a 135mm lens from a camera position further back from the subject.

Shot with a 40mm lens with a camera position closer to the subject


In this image of the bridge Sur le Pont d'Avignon shot with a 70mm lens we see some perspective compression.
In this image of he bridge shot from s different view point and with a larger focal length lens ( 450mm) the increased compressed perspective makes the lines of the bridge feel strange. Notice how people closest to the camera are nearly the same size as those at the far end of the bridge.




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