Exposure In Photography : Complete Guide (exposure time, buld function, metering)

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The exposure:

The shutter speed:

The shutter speed, also known as exposure time, determines the length of time in which the shutter is open or activated and defines how long the image sensor is exposed.

The shutter of a camera can be mechanical or electrical. In the case of a mechanical shutter, the image sensor is covered by a kind of curtain that releases the image sensor when the shutter release is pressed for the previously selected shutter speed and then covers it again. In the case of an electrical shutter, the image sensor is only switched to light-sensitive via the previously set shutter speed; he no longer has any mechanical parts.

In night photography, a longer exposure time is often used because of the difficult lighting conditions. Depending on the application, this can range from a few seconds to several hours. This is necessary because your camera's image sensor always needs the same amount of light to expose a picture with adequate brightness. While during the day and in bright sunshine an exposure time of a few tenths of a second is enough to expose the picture sufficiently bright, your camera needs correspondingly longer at night and in low ambient light to produce a sufficiently brightly exposed picture.

You dose this amount of light with the help of the exposure time. It does not matter whether a lot of light hits the sensor for a short time or whether it has to be exposed to less light for longer. Your camera should therefore support the ability to manually adjust the exposure time. In image mode "M" you can set a manual exposure time of a maximum of 30 seconds for most camera models, for other manufacturers such as Olympus for a maximum of 60 seconds.

The seconds are indicated on the display with a quiff. 30 “means that the exposure time is set to 30 seconds. If these quotes are missing, it is 1/30 seconds, which of course is many times shorter than 30 seconds.

For night shots with very little ambient light, however, exposure times of more than 30 seconds are often necessary. This is where the Bulb mode comes into play. The amount of incidence of light and thus also the length of the necessary exposure can also be regulated with the use of the aperture.

An exposure time of 4–8 seconds is a good choice to start with.

The bulb function

The bulb function is another manual mode and is usually identified with the letter "B". It is used to increase the exposure time over a period of 30 seconds. Some camera manufacturers do not assign an extra mode “B” under the image mode. Here you can increase the exposure time in "M" mode until you reach the bulb mode beyond the maximum exposure of 30 seconds. In contrast to the conventional manual mode "M", the shutter speed cannot be set to a specific value here, but is always set to the value Bulb. In this case, bulb means that the camera exposes as long as the shutter button is pressed.

With some camera manufacturers, you can choose whether the camera exposes as long as the shutter release button is pressed, or whether you want to start or end the exposure time by briefly pressing the shutter release button. With the help of the bulb function, it is possible to achieve very long exposure times that extend beyond the normal period of 30 or 60 seconds. When using the bulb function, it is very helpful to use a remote release so that you do not have to press the camera shutter continuously during an exposure and thus avoid camera shake. When using a remote release, you then also have the option of permanently pressing the release button, letting it click into place or starting and ending the exposure time with a short press.

For the thunderstorm photo, for example, the bulb function was used because it allowed us to determine the exposure time exactly. If there were more lightning bolts in the sky, we simply exposed longer, if there were fewer, we let go of the release button sooner. You can find out how to take such thunderstorm photos in our article " Tips & Tricks for Thunderstorm Photography ".


The automatic exposure:

Exposure warning:

If the interaction between shutter speed and aperture setting is not right, it can happen that your photos are exposed too brightly or too darkly. If too much light hits the image sensor, individual image areas or the entire photo will be overexposed. If the image is exposed too briefly, it will appear black in the insufficiently exposed areas. In both cases, too much or too little light has hit the image sensor, so that overexposed areas glow in pure white and underexposed areas appear in deep black. The pixels in these areas then no longer contain any image information and can no longer be corrected in a subsequent processing in the RAW converter. To avoid this problem, most cameras have a so-called exposure warning, Marks the areas that are too bright or too dark in the image and flashing them. Overexposed white areas are then usually displayed in red and underexposed black areas in blue.

Exposure metering:

However, in order to adapt your exposure to the ambient conditions right from the start and to avoid overexposure or underexposure, your camera carries out an internal exposure measurement. If you take photos in an automatic program such as program automatic (P), aperture priority (Av) or shutter priority (Tv), the camera uses the exposure measurement to select the correct settings for aperture and shutter speed.

The exposure measurement detects how much or how little light hits the sensor and whether this amount of light is sufficient to expose the image sufficiently. The sensor always tries not to expose your image too light or too dark. So if you want to photograph a bright white winter landscape, for example, your camera will automatically select a setting for shutter speed and aperture based on the exposure measurement so that the image is neither too bright nor too dark. Therefore it appears gray in this case. If, on the other hand, you are photographing a dark night landscape, the exposure metering of your camera will determine that little light hits the sensor. She will then set the shutter speed or aperture settings to a neutral value. Often times, this exposure measurement does not lead to the desired results and you have to correct your exposure manually. In this case, exposure compensation is used.

Exposure compensation:

With some subjects it can happen that the exposure metering of your camera determines the settings for aperture and shutter speed incorrectly, which leads to incorrect results. In this case, your photos are either exposed too light or too dark. In the example of the white winter landscape to be photographed, it is desired to expose the motif in such a way that the bright white mood of the snow comes into its own. However, the exposure metering selected the settings for the image in such a way that the entire photo is exposed in a neutral gray. Exposure compensation is used to correct this exposure. You can either increase or decrease the light value, which is indicated by the letters "Ev". If the value is increased to +1 Ev, for example, more light reaches the sensor and the image becomes brighter; if the EV value is reduced to -1, less light reaches the sensor and the image becomes darker. The exposure correction is usually displayed on the so-called light balance. This usually ranges from -3 through 0 to +3. Negative Ev areas darken or shorten the exposure time and positive EV areas brighten or lengthen the shutter speed.

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