How to use contrast to take photos

Contrast is mainly refers to the range of film density. That is to say, from the most thin shadow parts to the brightest highlights part. If a film density range is very large, it is called high contrast of the film, a film if its density is small, it is called the low contrast film.

Is what determines the contrast, the first is due to the contrast of scenery, that is the value of the actual scene surface reflective. If you place your subject to appropriate exposure and the tone of your subject range from highlight to deep shadow, then get a high contrast of the film. : (shoot a ski), for example, shooting a scene is broad surface of the snow, and slide skiing man dressed in a black hooded jacket, have the sun behind the surface of the snow, this scene will produce a strong contrast of the film.

Instead of a normal exposure of the film is a lighthouse, the lighthouse in the ocean mist environment, such a scene can produce a flat lower contrast of the film, if this film is a normal development.

A picture with a whole lighthouse. The exposure is the second factor of contrast, if you put your film big overexposed, it will reduce the contrast, even though the development is normal, contrast will be lower. In order to understand how this would happen, you should know about the photosensitive characteristic curve in the photographic film or H - D curve. It is a basic tool of photographic theory. This curve is called: scientists uncovered two black Del and DE law in the name of the field. It was developed in 1890 and used to represent a method of photographic performance, this curve is called characteristic curve. (also known as the curve: D - I 'OGE curve), have said is the accumulation of silver and exposure, under a certain degree of development, the relationship between can see exposure, the greater the accumulation of silver, the more at a fixed point is so before.

In the curve of each toe exposure has increased, only makes the density increases slightly, after arrived at the shoulder, exposure for every increase is not in proportion to the increase of density. Only between the toe and shoulder, straight and curve of the paragraph whenever exposure has some increase, the density is always with the increase of scale.

It have anything to do with shooting film and development, when the film exposure, if excessive exposure, and highlights the tone went onto his shoulder, and the middle tone is still in a straight line sections, which leads to an intermediate tone and highlights tone contrasts between small negatives, so too much will reduce contrast is overexposed.

On the other hand, if it is underexposed film, so the tone that highlights part to characteristic curve of the linear section, and the tone or the shadow part in the middle of the picture is still in the toe, the results highlight the tone of the density than the middle tone or tone increased density shadow part some faster, and this leads to a high tone and middle tone or shadow part contrast between the large plate, so it can be said that the underexposure can increase.

As the film overexposed exposure can provide larger capacity, namely, than at the time of underexposure can provide larger exposure degrees, so you would rather overexposed, if it is a common scene, overexposed in most of the film may have five or more levels of exposure degree, without the highlights of the detail is lost, but can't underexposure, such as a common scene let it sent two levels of exposure, shadow part details will be completely lost. Overexposure except overexposed very serious will reduce the contrast.

Photosensitive characteristic curve, contrast and contrast enhancement curve can be said that H - D density and the relationship between exposure and development. How development affects the density and contrast, this basically has two:

1. Increase the development of the film increases contrast;

2. Reduce enhancement is contrast.

How to increase or reduce the degree of development, the development time is normally increase, increases the degree of development. Another way is to increase the temperature of developer, which can also increase the enhancement degree, because the higher the temperature solution is more energetic. The third way is to change a kind of dynamic strong developer.

In order to understand how development affects the contrast, now you can use a simplified model. Presuppose that there are ten layers on silver halide grains in the film to accept the area of light, this is a simplified model, not so in the real, but is very much, I'm afraid there are thousands of layer thickness, in some parts of millions of layer thickness. Now assume that every minute of development will show a layer of silver halide grains, 5 minutes to show five floors, 10 minutes 10 layers to show. Let's take a look at one minute after a minute in the past, imaging what will happen.

At the end of the first minute, developed the first layer, this includes every part of the film by light area. If it stops the developing, so only the contrast is due to there is absolutely nothing that part of the light and of any light that part of the difference between silver accumulations. At the end of three minutes, shadow part of the accepted at least part of the light show a layer of two layers or three layer of silver film, also it is accepting exposure through the development of different thickness of the silver shade, strong specular part but is far from show to? Because only in the third layer, though has been affected by light up to the tenth floor, but in three minutes of this, in the film is also only a small contrast.

To continue developing a longer time increases the contrast between the areas, it is some is close to full development area, and those who are far from fully developing area. Therefore increase the enhancement increases contrast, reduce enhancement decreases contrast.