Project 3: Focus with different apertures

[3 photos]

A row of things seen from an angle: e.g. railings, parked cars, terraced houses….Stand at an angle with a tripod….Focus on an obvious point, somewhere near the middle. Take 3 photos using the smallest, midpoint and midpoint range of  aperture settings.

ISO 100, f/4

At the lens’ widest aperture (f/4) only the tin of baked beans is in sharp focus in the centre third of the frame. Both the foreground and background are out of focus.

ISO 100, f/10

At f/10 more of the tins are in focus in the centre of the frame.

ISO 100, f/22

At f/22, the smallest aperture, the entire scene is in focus.

The main difference between the images is that the one with the smaller aperture setting (f/22) has more of the image in focus than the the largest lens aperture of f/4. Therefore a smaller aperture means that objects can be in focus over a wide range of distance (depth of field). This was a big surprise to me. I had expected that the bigger the aperture the more of the image that would be in focus.

This project has been a sticking point for me for a while. I had been wanting to get on with completing the assignments and the visual aspects of arranging the subject(s) in the frame. However I recognise that all of that is pointless if the lens is not set at the right aperture to create the desired effect. I used to be quite lazy in my photography by keeping the aperture set at it’s smallest f/stop….and then always wondered why only parts of the image were in focus! This has lead me to investigate how depth of field can be affected. A recent article in the Photo Plus magazine (Spring 2010, Issue 34 p 68-69) had a great article explaining depth of field.

Depth of Field (dof)

  • the areas of the photo both in front and behind the main focus point
  • affected by aperture, subject, distance, focal length, film or sensor format

Large Aperture

  • small f-number
  • shallow depth of field
  • anything behind or in front of the main focus point will appear blurred

Small Aperture

  • large f-number
  • greater dof = objects in front and behind appear sharp.

Depth of field can be altered by:

1. Changing the aperture – wider the aperture = less depth of field

2. Changing the focus distance -closer to the subject you’re focusing on = less depth of field

3. Changing the focal length – the wider the lens (shorter the focal length) = more depth of field captured

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