Aperture

Diagram of F stops and aperture structure.




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The aperture is an iris that sits at the back of the lens and is designed to control the amount of light that reaches the film/sensor which records the image. The aperture is constructed from a series of metal slates which are interlinked. At its centre is a hole which can be made wider or smaller, the diameter of this hole is measured as an f stop, the bigger the whole the smaller the f stop. The changing of the aperture in modern cameras is often done by adjusted a ring on the outside of the lens.

The aperture has another function as well as controlling light; it controls the sharpness of the image that is captured. The measurement of sharpness is photography is known as “depth of filed” and the wider the aperture the shallower the depth of field and visa-versa. To ensure that the full image is captured on the film/sensor, there has to be a measured amount of light that hits its surface. This measurement is known as exposure and is made of two calculations, the amount of light that is passing thru the aperture and the time the film/sensor has to react with it. The control of the amount of time the film/sensor is exposed is determined by the shutter

F stops and focus range

Most photographers want to achieve a good level of focus in their images. Focus can be used in composition but the general rule is to achieve to the greatest level of sharpness in a photograph.

Selecting an f stop when choosing exposure levels not only determines the speed of the shutter it also indicates the level of focus in the final image.A wide aperture such as f 2.8 means that the depth of field will be shallow. This means that only a small area around the point of focus on an image will be sharp. Wider f stops are often used when light is limited or for effect such as blurring backgrounds to isolate the subject. Shallow depths of field are good to use in portraiture.

Smaller f stops such as F16 give a greater depth of field which means more detail in the final photograph is in focus. As the aperture is small and a less light is filtering thought the lens, a slower shutter speed is required to achieve the correct exposure levels. Using smaller f stops in landscape photography means more of the scene is captured in focus.

Using a shallow depth of field for creative effect

This image shows the creative effect of using a shallow depth of field. The foreground detail is in focus but the background is blurred. This focuses the eyes onto the detail of the sand.

EXERCISE- FOCUS AT DIFFERENT APERTURES
Take at series of images of the same subject at different aperture's compare the results


The series of images below show the sames image all taken at different aperture settings.

















The first image was taken at aperture 4.5, a wide aperture which gives a shallow depth of field.
This means that only a small area of the point of focus is sharp. As you can see the background and foreground are less sharp than the other images. Using a wide aperture when taken a close up subject can help distance the subject from the background as less of the background will be sharp. It helps focus the viewers eye onto the subject of the photograph.

The second image was taken at aperture F8. This is an average F stop which gives an mid level of sharpness in an image. If you are taking lots of shots and have little time to adjust the aperture setting ie at an event, it is good to set your camera at this aperture level so most of your image will be in focus. As you can see from the detail in the image the background/foreground is mostly in focus. The subject ( the lamp) is sharp.


















The final image was taken at F22 which is a very small aperture. This gives a greater depth of field as you can see that the subjects in the background are in focus. A smaller aperture is ideal to use when you image requires for the image to be sharp. An example could be when you are shooting landscape scenes and therefore require the whole vista to be in focus.


OUTCOME
noted the variation on exposure as well as sharpness, with different aperture settings. Ideally require greatest level of sharpness for reproduction or enlargement.LEARNING NOTES/COMMENTS
experiment with exposure settings at different exposure settings. Use aperture priority and note shutter speed changes