Aerial perspective is a term banded about by photographers and artists, but very often misunderstood.
It does not mean perspective as in, a scene from up in the air, a picture taken from an aeroplane or hot air balloon.
Aerial perspective is the effect of distance or depth caused by atmospheric haze. It looks like this:
Notice the colour shift to lighter blue?
Because the air contains impurities and minute particles of water, light travelling through it for any distance becomes scattered.
The greater the distance, and the more particles in the air, the more light is scattered and the more intense the effect of the haze.
The result is that objects appear weaker in tone and colour the farther away they are from your viewpoint.
Contrast and detail are lost on distant horizons., there are no rich blacks and the colours appear increasingly bluer.
This is the effect known as aerial perspective, and it is more noticeable at high altitude and over water because more ultraviolet light is present in the atmosphere.
In photography this natural phenomenon is exaggerated because, whereas the eye cannot see ultraviolet radiation, cameras are very sensitive to this part of the light spectrum.
Objects appear lighter in the distance, and the effect is often so great that a picture of a series of hills can look like a group of cardboard cut-outs.
Controlling haze
In black and white photography the effect of aerial perspective can be quite well controlled by a choice of coloured filters, a bluish filter intensifies the effect giving more depth in a picture, while a red filter reduces the haze effect and the distant objects are seen more clearly.
Check out this full set of filters from K&F which looks pretty handy if you’re a landscape photography enthusiast.
In colour photography however, control is rather more limited.
If you were to use a deep red filter to cut out the haze you would get a deep red picture as a result, you might have got rid of the haze but the colours would be all over the place.
When there is not too much haze the effect of aerial perspective can be reduced by using a skylight filter. This absorbs some of the ultraviolet light, but only works in mild cases. Hoya, Hama and Gobe/Urth filters are all good.
A polarising filter can also be used. It deepens the blue of the sky and consequently makes the picture appear clearer near the horizon. The most effective control when working with colour, however, is making use of depth of field. If the foreground subject is in focus, it can be visually separated from the background by ensuring that the background is thrown out of focus. Even with a relatively close background, the hazy impression makes it appear to be farther away simulating aerial perspective.