Project 2: Focus With A Set Aperture

The aim of this project is to show that by using a wide aperture the depth of field can be narrowed to make a small part the image stand out.

I took a series of 3 photos at the old Blackfriars bridge across the Thames focussing each time on a different column (far, middle then near). Each shot was taken at standard focal length with a aperture of f/3.2.

When viewed, there is very little discernable difference between the shots (and therefore I have only included one of the shots here). Further reading about the subject shows that there is more to reducing depth of field than simply using a wide aperture. Frost (1993, p 31) states that:

"Whenever you take a picture an area extending in front and behind the point you focus on will also come out sharp. This area is the depth of field, and its size varies depending upon three things:

• The aperture set on the lens. The smaller the aperture, the greater the depth of field. If you take a picture using an aperture of f/16, much more of the scene will come out sharp than if you use a large aperture such as f/2.8 or f/4.
• The focal length of that lens. The shorter the focal length the greater the depth of field is at any given aperture. A 28mm wide-angle lens will give far more depth of field when set to f/8 than a 300mm telephoto lens set to f/8.
• The distance between the camera and the point focused on. The further away the point of focus is, the greater the depth of field for any given lens and aperture. If you use a 50mm lens set to f/8, depth of field will be greater if you focus the lens on 10m than it will focused on 1m.

Taking these three points into account, if you want minimal depth of field so your main subject stands out and everything else is thrown out of focus, use a telephoto lens set to wide aperture such as f/4."

In order to get the images I require for this project I will repeat the exercise using a wide aperture at a longer focal length and have the points of focus closer to the camera....

These photos were taken from around 2 metres with a focal length of 160mm at f/4 (each image can be seen at full size by clicking on it).

In the first picture (left) I
focused on the red train.

In the second picture (right) I
focused on the blue train.

In the third picture (left) I
focused on the green train.





I prefer the last picture (focused on the closest, green train) as it has the shallowest depth of field of all 3 shots throwing the other trains out of focus and drawing the eye to the subject.

29 July 2006
I used the shallow depth of field technique in these two photos that I took of the Meerkats at Birmingham Nature Centre.


The photos were taken from around 4-5 metres away with a focal length of 420mm and an aperture of f/4.5.