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D for Depth of Field
The reasons why?
Depth of field (DoF), it is one of the tools at our disposal for seeing, feeling and presenting an effective expressive photograph.
Why are Subject dominance and relationships important? Depth of field has a strong influence on what dominates the picture space and the way in which the viewer understands a picture. Depth of field is the zone of acceptable sharpness forward and behind the point of focus.
What you have to say with the picture can be strengthened by your choice of:
- Focal length
- Depth of field.
Exposure – the eternal triangle
For effective control of depth of field you must fully understand the Exposure Triangle. Without this knowledge your ability to control the camera and hence the power of your visual message will be weakened. What follows is a guide to give full control of depth of field.
With a fixed ISO rating, if you change the aperture to increase or decrease depth of field, the shutter speed will correspondingly be adjusted by the same number of f stops.
Be aware of the effect your choice of depth of field will have on the shutter speed and your ability to hand-hold a shake-free shot. This is particularly true in low light situations.
4 things you need to know about how depth of field is controlled
1 Sensor size
The smaller the sensor, the greater the DoF and the fewer options you have for control and limited DoF pictures. This is why compact cameras with minute sensors are great for close-up photography.
2 Focal length of the lens
Depth of field is reduced with a longer focal length lens and increased with a wide-angle lens.
3 Lens aperture
A small lens aperture (large f stop number) gives greater depth of field than a large lens aperture (small f stop number) – with the camera usually in Aperture Priority Mode
4 Distance to the point of focus
The closer any focal length lens is to the point of focus will reduce depth of field and soften the image in front of and behind the point of focus. An extreme example of this point can be created with a semi-fish-eye lens focused at it closest distance with its widest aperture, 0.3m distance at f2.8. These settings will soften the background, the critical part of this arrangement is the minimum focussing distance.
Embedding Skills Exercise
Here is a practical picture taking exercises to put the depth of field theory into practice.
Take a series of pictures with a minimum of five pictures in each.
A1 200mm Telephoto lens, focusing distance 1m, Aperture f4 (APSC 135mm, M4/3 100mm)
A2 200mm Telephoto lens, focusing distance 5m, Aperture f 16
A3 200mm Telephoto lens, focusing distance 1m, Aperture f 16
A4 200 Telephoto lens, focusing distance 5m, Aperture f4