Friday, 17 December 2010

Project: Focus

I saw this photo on the cover of The MOD's  E2E quarterly magazine. (There is no byline for the photograph so I cannot attribute it) It illustrates perfectly the impact of sharp focus with a shallow depth of field.

With the following images, I was looking for a shortened perspective and spotted these shop signs in a nearby street. However, the irregular and relatively greater distances between the signs meant it was not an ideal subject to illustrate differential focusing effectively. They do show that with a wide aperture, the depth of field is limited and that when the lens is focused on a foreground object, more of the background depth is thrown out of focus.

Lens focal length 130mm, f5.6 @ 1/50s

I focused on the tiled wall to the right of the image. The green sign is just out of focus and all of the background is blurred. 

The same camera settings with the lens refocused on the green sign. The tiled wall is out of focus, the background is in focus back to the brown and cream sign, beyond that it is blurred to infinity.

I had no tripod with me to provide consistent framing for this subect and realised I would need a better subject to show the objective of this exercise.

Exercise: Focus with a set aperture.

Objective: This exercise will demonstrate the effect that can be achieved using a wide aperture in a scene that has depth.

For this exercise I chose a row of six workstations in a classroom, set my camera on a tripod and focused on three points within the depth of the scene. I included two red objects as a reference point.
Camera settings: Zoom focal length 50mm, aperture f4.8, shutter 1/13s. Lighting: fluorescent tubes (colour corrected post processing)

1. I focused on the closest edge of the keyboard in the first workstation, resulting in a very shallow depth of field of about 5cm.

2. Here I focused on the nearest edge of  the second keyboard and it can be seen that the depth of field extends for approximately 30cm.

3. For this example I focused on the third workstation mouse and the depth of field extends to the fourth workstation mouse, a depth of about 60cm. (this can be more clearly seen from a larger print of the image)

The first image's restricted depth of focus tends to leave your eye at the foreground  and at the bottom of the frame. There is nothing to draw your attention into the picture. The third image does get your eye moving along the desk, searching for the focus area but when you find it,  it's too  narrow to hold your attention for long. (also, the red pen and folder have more to do with grabbing your attention)

I think the second image is the best. There is sufficient out of focus detail at the bottom of the frame to indicate depth and enough blur in the background to place the keyboard at the centre of interest. Adding the red objects to the image was a mistake so I have recoloured those objects grey, to show the distracting effect that they have.

What have I learned?

Selective focusing with a narrow depth of field achieved with a wide aperture can isolate obects within a scene and create a centre of interest. Use red in a scene very carefully if you don't want it to dominate or distract.

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