As one varies the aperture used to capture an image there is a discernible variation in the area of the image that lies within the acceptable limits of sharpness. In this exercise I explored this relationship by taking a photograph of a scene multiple times and varying the aperture each time.
In order to make comparisons on the effect of aperture upon the area of acceptable sharpness within a photograph it was important to capture the same scene multiple times using a variety of apertures. To achieve ensure that I would be capturing the same scene each time I fixed my camera to a tripod and did not move the camera throughout the exercise. Variations in the aperture used would require adjustments in the shutter speed to be made in order to achieve the same exposure in each photograph. I decided to allow the camera to adjust the shutter speed for me and set the camera to aperture priority mode.
I decided to use the trusty wall that I used in the previous exercise. My reasons for this were in part because I was attracted to the colours and texture within that wall and in part because the wall very clearly demonstrated differences in sharpness across the scene.
Results
In each of the photographs below I have marked boundary of the limits of acceptable sharpness.
In order to capture the above photograph the lens was set to it's widest aperture, f/2.8. The focus point was set to the middle of the frame and a sample picture was taken. Upon looking at the histogram on my camera I decided to apply a full stop of exposure compensation and set the camera to record the image in RAW format. This allowed me to capture a picture without any blown out highlights and which I could confidently underexpose in post processing without introducing noise. The area of the photograph within the acceptable limits of sharpness is relatively narrow and surrounds the focus point.
In the photograph above I set the camera to a middle of the range aperture, f/8. The area of the photograph within the acceptable limits of sharpness has grown significantly and is approximately double the size of the first photograph taken.
In the final of the three photographs taken in this series I set the aperture to the smallest available to me, f/22. One can see that the entire scene from front to back has been rendered within the acceptable limits of sharpness.
Summary
This exercise clearly demonstrated the effect of aperture upon the area of the photograph that is within the acceptable limits of sharpness. The creative opportunities that this offers the photographer are great. One can choose to render an entire scene in focus by using a small aperture or one can choose to isolate a subject from other elements within the scene by using a large aperture. While this is fine for static objects one must consider the effect of changing aperture upon shutter speed. For example, in order to render the entire scene within the acceptable limits of sharpness the shutter speed had to be increased to 2 seconds whereas at a wide open aperture setting of f/2.8 the shutter speed was only 1/30s. If the subject had been moving this would have meant that at a wide open aperture one may still have captured a sharp subject. However at a narrow aperture the subject would have been extremely blurred due to the effect of motion. In other words, while aperture can be used to capture a photograph with the required area within the acceptable limits of sharpness one must also consider the impact this will have on shutter speed if the camera is hand held or if the subject is moving.
In order to make comparisons on the effect of aperture upon the area of acceptable sharpness within a photograph it was important to capture the same scene multiple times using a variety of apertures. To achieve ensure that I would be capturing the same scene each time I fixed my camera to a tripod and did not move the camera throughout the exercise. Variations in the aperture used would require adjustments in the shutter speed to be made in order to achieve the same exposure in each photograph. I decided to allow the camera to adjust the shutter speed for me and set the camera to aperture priority mode.
I decided to use the trusty wall that I used in the previous exercise. My reasons for this were in part because I was attracted to the colours and texture within that wall and in part because the wall very clearly demonstrated differences in sharpness across the scene.
Results
In each of the photographs below I have marked boundary of the limits of acceptable sharpness.
Summary
This exercise clearly demonstrated the effect of aperture upon the area of the photograph that is within the acceptable limits of sharpness. The creative opportunities that this offers the photographer are great. One can choose to render an entire scene in focus by using a small aperture or one can choose to isolate a subject from other elements within the scene by using a large aperture. While this is fine for static objects one must consider the effect of changing aperture upon shutter speed. For example, in order to render the entire scene within the acceptable limits of sharpness the shutter speed had to be increased to 2 seconds whereas at a wide open aperture setting of f/2.8 the shutter speed was only 1/30s. If the subject had been moving this would have meant that at a wide open aperture one may still have captured a sharp subject. However at a narrow aperture the subject would have been extremely blurred due to the effect of motion. In other words, while aperture can be used to capture a photograph with the required area within the acceptable limits of sharpness one must also consider the impact this will have on shutter speed if the camera is hand held or if the subject is moving.
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