Exploration of Relationship between ISO, Shutter Speed and Aperture.

These photos were taken on October 9^th 2011 between 4.00 and 5.30pm. Lighting was cloudy but bright, but windy.

The lens used was Zuiko Digital 40 – 150mm. A tripod was used for all photos to stabilise the camera, eliminate camera shake and allow slow shutter speeds to be chosen.

Three f-stop numbers were used – f/5.6, f/11, f/22

Three ISO settings were chosen ISO 100, ISO 400 and ISO 1600

These 6 settings were combined with a variety of shutter speeds to examine the effects produced.

Expected effects:

• As the f-stop number increases the amount of light entering the camera is reduced so for the same ISO setting the shutter speed will need to be reduced.

The ratio will be a reduction of ¼ for each increase in f-stop number; conversely the shutter speed will have to increase fourfold for each increase in stop number

• As the ISO number is increased the light sensitivity of the camera sensor will increase fourfold, so for the same f-stop number the shutter speed will reduce by ¼.
• ISO 100 will produce a crisper image than ISO 1600
• ISO 1600 will produce a ‘grainy’ or ‘noisy’ image
• Photos taken at slow shutter speeds (<1/60^th second) will show any movement of the subject (e.g. movement of branches)
• Photos taken at f/5.6 will have a narrower depth of field than photos taken at f/22

Images produced:

Photographs of 3 subjects were taken:

Prunus tree bark

Willow tree

Berberis plant

Prunus bark: 

Focal length 73mm

f/5.6; ISO 100; 1/5^th second

f/5.6; ISO 400; 1/20^th second

f/5.6; ISO 1600; 1/80^th second

As can be seen to maintain a similar exposure as the ISO number increases the shutter speed can be reduced by ¼

The following 2 photos show how by increasing the ISO setting, but leaving the f-stop and shutter speed constant the photo becomes overexposed.

f/5.6; ISO 400; 1/5^th second

f/5.6; ISO 1600; 1/20^th second

Berberis Plant:

Focal length 83mm

The following 2 photos show how by leaving the f-stop and shutter speed constant and reducing the ISO setting the photo becomes underexposed.

f/5.6; ISO 1600; 1/160^th second

f/5.6; ISO 400; 1/160^th second

Willow Tree:

Focal length 45mm

The following 2 photos show that by leaving the shutter speed and ISO setting unchanged, but increasing the f-stop the photograph becomes underexposed.

f/5.6; ISO 1600; 1/200^th second

f/11; ISO 1600; 1/160^th second

The next three photos show how at ISO 400 an increase in f-stop meant that the shutter speed also had to increase (approximately fourfold) to maintain a similar exposure.

f/5.6; ISO 400; 1/60^th second

f/11; ISO 400; 1/13^th second

f/22; ISO 400; 0.30 seconds

It is also apparent that the motion of the willow branches is almost frozen at f/5.6, whereas the branches show blurred movement at f/11 and f/22.

Health and Safety Concerns.

Within my own garden access is not an issue. Safety concerns include not being foolish in my personal safety e.g. climbing trees for viewpoints. The main issue is not to compromise the well being on any bird or creature within the garden.