Exposure

Exposure is the measurement of the amount of light exposed to the film/sensor, this exposure calculation is the relationship between the size of the aperture ( f stop) and the speed at which the shutter passes over the film plane( shutter speed).

There needs to be a perfect balance between the aperture and the shutter speed to ensure correct exposure. It is important to achieve the correct exposure so that all the detail of the image can be captured in the final print. It is important to capture both the detail in areas of highlight and of shadow.

If the film/sensor is subjected to too much light then the image becomes “over exposed” meaning that area of the image that has a lot of light will be washed out and the detail will be lost. Conversely if the exposure is too low, then the image will be “under exposed” and all the detail would be lost in the area of shadow. If an aperture is set at f16 then its diaphragm is small, this means a limited amount of light will be exposed to the film. Therefore the shutter will have to pass across the film plane at a slower speed to allow the correct amount of light to reach the film. If the aperture is set at f/2 then the aperture is wide, which means that more light is passing through the lens, therefore a faster shutter speed is required to achieve the correct

exposure level.

To calculate exposure you firstly need to understand the light that is available. You can measure light in two ways. Firstly there is using a hand held light meter.You tell the light meter the speed at which you are taking the image and it will give you a recommend aperture setting. You can also indicate the lighting conditions being used i.e tungsten, natural or flash. The meter also allows you to take several readings from around different areas of the subject. You can use these readings to calculate the most ideal aperture setting to achieve the most ideal exposure level. It is important that you ensure that the shutter speed level selected will allow you to achieve not only good exposure levels but also a good level of sharpness in the final image.

The second way to measure light is to use the internal light meter of your camera. This is call THROUGH THE LENS metering or TTL for short. This is where the camera will take an average light reading form around the point of focus and suggest an exposure level. You can set you camera up to measure light in different ways. If you have set the camera up to read more that one area in the image this is will you a better average and may capture areas of both highlight and low light. Most photographers will use this on location but are more likely to meter in the studio.

Aperture priority.

Using the camera can help when setting the correct exposure level. If you require a greater level of sharpness in the final image then you require a small aperture such as f16. This means that the diameter of the aperture is very small not letting a lot of light through the lens to the sensor. You will therefore require a slow shutter speed. Using the aperture function means that once you have selected your required aperture setting once the camera has read the light coming through the lens it will suggest to the user a ideal shutter speed.

Shutter speed priority

Just as aperture priority, you can suggest your ideal shutter speed and then again once the camera meters the light it can suggest the ideal aperture setting to achieve an average exposure.

It is important the user understands the balance of the suggested settings as the photographer may want to adjust the settings to reflect the subject, for example if you are shooting a subject in detail then you need to ensure that the image is sharp. Therefor you must use a smaller aperture setting. If these means that the shutter speed is slow, it may require you to use a tripod.

Bracketing

One way of ensure you can capture the ultimate exposure level is to take images at a stop above and under the suggested setting. An F- stop represents an the next aperture level. eg f 5.6 is one stop above f 4.5. You can then view these images and judge the most ideal in both exposure and sharpness.

Project - Exposure

FRINTON

over exposed image. The image is burnt out in areas of highlight in the sky. The detail in the foreground is also washed out. It is important to look at the histograms of the image as burnt out whites are unlikely to be pulled back in photoshop.

Bracketing exercise

Suggested setting from the camera which was an average of both area of highlight and shadow. I fell that I should have stopped down one more as the highlights are still too burnt out

two stops under give better definiton of the areas of highlight but the foreground is too dark. This image could be alterned in photoshop to bring some light into the image.

Two stops over.... completley overexposed.