Questions about photography (experts come in)!

The following contents mainly refer to the use of film cameras, but some of them are still helpful to the digital age.

Correct exposure is the key to ensure the success of photos. In actual shooting, despite the help of exposure meter, beginners often encounter the problem of inaccurate film exposure. This is because the situation of photography is very complicated and there are many factors that affect normal exposure. If you are not careful, you will make mistakes. Here, list ten factors that affect normal exposure:

1. Did not pay attention to the influence of the environment on photography. Under the same weather conditions and different shooting environments, the demand for exposure will also change. For example, in the snowy Yuan Ye, or the vast seaside, because of the strong reflected light generated by the environment, the exposure is about one file less than that of shooting in the general environment.

2. After using the film with special sensitivity, exposure value didn't correct it in time. The membrane we usually use.

The photosensitivity is 1S0 100. When using films with other sensitivities such as IS0200 and IS0400, be sure to take photos in time.

The exposure should be corrected, the aperture should be reduced or the shutter speed should be increased.

3. The result of too bright background. If you shoot a portrait outdoors with a large sky as the background, you should use auxiliary light to improve the brightness of the figure and shorten the gap between people and the sky. If you don't do this, if the exposure is based on a bright background, the characters will be underexposed.

4. Reciprocal exchange rate is invalid. Sometimes the film emulsion receives too much or too little light, and the exposure time is too long or too short, and the same exposure cannot produce the same photographic effect. For example, when the illuminance is 1000 lux and the exposure time is 1 sec, the density of the generated silver shadow is greater than that when the illuminance is 1 lux and the exposure time is 1000 sec. Therefore, we should consider this factor and increase the exposure appropriately when we carry out slow exposure with small aperture (slower than 1/2 seconds).

5. The scope of use is beyond the limit. Some people think that a fool's camera is equipped with a flash, and there are automatic metering and exposure devices, so when shooting in some dark environments, the flash is often turned on without distinguishing the situation, but the result is often not ideal. This is because the flash index on the stupid camera is very small, and the effective range is only within 3 meters. When people are 3 meters away, there will be underexposure.

6. Using flash as lighting source, exposure value cannot be calculated correctly according to the index of the lamp.

7. When shooting, a color filter is added to the lens, but the exposure value is not increased accordingly, which will also lead to underexposure.

8. Seasonal factors are not taken into account. Throughout the year, the intensity of the earth's exposure to the sun varies. In summer, the sun shines directly on the ground, with the strongest brightness; In winter, the sun shines obliquely on the ground, with the weakest brightness. The brightness of spring and autumn is between winter and summer. So the exposure value used in the same scene in different seasons should be different. Spring and autumn; The exposure is one step higher than that in summer; The exposure in winter needs to be two grades higher than that in summer.

9. I didn't pay attention to geography. Due to the different areas where the subject is located, the intensity of light will be different. The shooting location is close to the equator with strong light; Away from the equator, the light is weak. Therefore, every increase in geographical latitude of 15 degrees will increase the exposure by half a step. As far as China is concerned, under the same shooting conditions, the southern region should be one level smaller than the northern region. The altitude of the subject also affects the exposure. The higher the altitude, the thinner the air, the less sunlight the atmosphere absorbs and the brighter the light. Therefore, for every 3000m elevation, the exposure should be reduced by one level.

10. The roughness and smoothness of an object's surface and the depth of its color will affect its ability to absorb and reflect light. Therefore, even under the same light, we should seriously consider the ability of the scene to reflect light. For example, snow, water, beaches and other scenery have strong reflective performance, and the amount of light will be appropriately reduced compared with ordinary scenery; When shooting objects with rough surface and dark color, such as bushes and coal piles, the exposure should be appropriately increased compared with ordinary scenery.