Focus.

Exercise: Focus with a set aperture
For this exercise I found a scene which presented three subjects at varying distances from the camera. I used a fixed focal length lens and selected an aperture of f1.4 to highlight the effects of different points of focus.

For Photograph 1 I focused on the tree nearest the camera.

Photograph 1. 30mm @ f1.4

In this picture the attention is immediately drawn to the detail of the tree to right of the frame. The rest of the image has been thrown out of focus by a combination of the wide aperture and the proximity of the point of focus to the camera lens.

For photograph 2 I set the focus on the tree to the left of centre.

Photograph 2. 30mm @ f1.4

Now the attention of the viewer has been moved away from the tree in the foreground which appears blurred and lacking in detail. The point of focus has moved to the tree to the left of centre. However, despite the aperture remaining at f1.4, the area of sharpness within the picture appears to extend deeper into the image. I believe this is due to the point of focus being farther away from the camera than in photograph 1.

For photograph 3 I focused on the distant tree in the centre of the frame.

Photograph 3. 30mm @ f1.4

The tree in the foreground appears to be even more blurred than in photograph 2. The middle tree to the left of centre has lost some sharpness but still retains an amount of detail despite the widest aperture being set. The trees at the back of the image are more detailed now.

Of the three images here, I prefer photograph 2. The point of focus on the tree to the left of centre immediately draws your attention to it, and the way the tree is leaning to the right then gently takes your eyes to the trees at the back of the frame.



Exercise: Focus at different apertures.
I set up a scene indoors for this exercise, using just the ceiling light. I lined up a row of model cars, deliberately placing the car with the strongest colour in the centre and using it as my point of focus. With my camera mounted on a tripod I selected my widest aperture and the appropriate shutter speed and took Photograph 1

Photograph 1. 1/60sec @ f1.4

With the aperture wide open the depth of field is very shallow. The limit of sharpness really only covers the car in the centre of the line up with the models at either end being completely out of focus.

I then adjusted the aperture to a mid setting and applied the necessary shutter speed for photograph 2.

Photograph 2. 1/2sec @ f8

With the aperture stopped down to f8 there is now clearer detail in more of the image as the limit of sharpness has increased to cover the models either side of the centre car. Additionally the cars at either end of the row, while still out of focus, are significantly sharper than they appeared in photograph 1.

Now I set the aperture to it's minimum setting of f16 before taking photograph 3.

Photograph 3. 2secs @ f16

In this photograph the limit of sharpness has extended almost to the edges of the frame. All the models now seem reasonably sharp although the outside cars still appear a little soft. Stopping down to the minimum aperture brings most of the frame into focus but at the expense of having to use a longer shutter speed as clearly demonstrated here with an exposure of two seconds.