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.

Images of Scarborough Oct 1st 2011

Taken at 11am 1^st October 2011: A bright sunny day with clear blue skies. Using hand held Olympus E520 camera with 40 - 150mm and 70 - 300mm lenses.

These photographs were taken whilst away for a weekend in Scarborough whilst walking in the public gardens above the Esplanade.

f/5.6; ISO 400; 1/25 second; focal length 42mm (Image Stabilisation ON)

This photo of a decaying leaf has achieved my aim of a narrow depth of field. 

Ideally in bright sunlight a film speed (ISO setting) of 100 is preferred. This would lead to an image as crisp and clear as possible. To achieve this narrow depth of field an aperture as wide as possible is required (f/5.6 or less), which for ISO 100 would require an increased amount of light to reach the sensor for a correct exposure i.e. a slower shutter speed. However for a focal length of 42mm a minimum shutter speed of 1/40 second is required; with image stabilisation on the camera this could be reduced to 1/25 second.

The leaf itself appealed to me as a subject because of its:

• Colour – so grey in contrast to the vivid green of the surrounding leaves
• Shape – almost square, but with indistinct edges
• The holes that you can see straight through
• The concept of decay which in itself will lead to new growth amidst the life shown by the bright green leaves

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f/5.6; ISO 400; 1/40 second; focal length 300mm (Image Stabilisation ON)

I like this photo even though the ladybird did move to the wrong side of the leaf!! – Or did it? The image is very simple with just a few simple lines. The leaf on the left is highlighted and leads you to the leaf at the front which guides you up to the ladybird. The contrast in texture between the two leaves is also interesting. 

f/5.6; ISO 400; 1/60 second; focal length 300mm (Image Stabilisation ON)

This image has a narrow depth of field, and the subject (ladybird) is quite central. The mould spots on the leaf provide an interesting contrast to the green of the leaf. However the image is less satisfying. The wings of the ladybird are reflecting back the sunlight that was behind me, proving a distraction. I also think that cropping to move the ladybird to the left might help.

f/5.6; ISO 1600; 1/60 second; focal length 179mm (Image Stabilisation ON)

I really like this image. The wide aperture has given a narrow depth of field so that the whole focus is the flower yet there is a hint of the leaves behind; the 2 main colours (green and blue) complement each other well. I think the size of the flower is correct – any larger and it would overpower the whole image. At the moment the image is saying “Look at me – simple but beautiful”. Possibly moving the image to the left to include the ‘Rule of Thirds’ might help, but without seeing it I am unconvinced.

However, the use of ISO 1600 could well make the image very ‘noisy’, and reduces the crispness of the petals.

f/5.6; ISO 1600; 1/500 second; focal length 300mm (Image Stabilisation ON)

The high ISO setting has certainly created much noise, and since the wasp was not flying a slower shutter speed with ISO 100 or 200 may have been equally effective. However the fun bit is the 2 small insects to the left – I couldn’t even see them with my naked eye. Close up photography often shows such things e.g. for bird identification.

f/5.6; ISO 1600; 1/160 second; focal length 263mm (Image Stabilisation ON)

Again ISO1600 gives the photo too much noise. However the image is pleasing. It might need cropping to move the leaf to the left. I like the colour range with yellows both top left, top right and central (this effect might be lost if cropped); and the decaying leaf folding over and out of focus. Wasps are an image (by association) of ‘decay’ (as they feed on rotting fruit) and this image I feel shows the beauty of decay.

f/5.6; ISO 1600; 1/100 second; focal length 300mm (Image Stabilisation ON)

Again the ISO gives the image too much noise. The colour range is pleasing – yellows, browns, greens through to black. The reflection from the water helps to focus the eye on the struggling wasp, aided by the two vertical leaves and the pentagonal shape made.

f/5.6; ISO 1600; 1/320 second; focal length 300mm (Image Stabilisation ON)

This could have been a fascinating picture. ISO 1600 gives too much noise; use of a polarising filter may have reduced the reflection (although possibly to the detriment of the image). The colours are subtle and complementary; the wasp doesn’t dominate but is positioned according to the Rule of Thirds. However it is the parallel shadow on the left which gives this photo its interest.

The next three photos are all of a squirrel. They all show movement and give an idea of the type of image I would like to achieve within my own garden.

The settings for all were:

f/5.6; ISO 1600; 1/400 second; focal length 300mm (Image Stabilisation ON)

I like the narrow depth of field, and think the slanting horizontal gives a sense of fun to the picture.

This captures the eye of the squirrel – unfortunately he is not all within range! He stopped!

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This captures his movement – but he was too fast!

Lessons to be learnt.

• To go out and try again
• To change ISO settings more frequently
• Not to assume that movement equates with a requirement for a high ISO setting
• To continue to consider the composition of the photo rather than ‘just shoot and hope’

Health and Safety Concerns.

The photos were taken in a public garden, so my access was limited to this area. I needed to be careful not to impinge on anyone’s personal space, nor to trespass onto private ground. I also needed to be aware of my own safety and the security of my camera and other belongings – not to leave items unsupervised as I concentrated on taking photographs. As always any photographs should not damage the area nor any animals.

ISO SETTING

What is ISO?

The ISO (International Standards Organisation) index is a system that was designed to calibrate the sensitivity to light of film emulsions.  This index is also used to calibrate the sensitivity of digital sensors to light. The ISO rating of digital sensors is based directly on film ISO, such that a 200 ISO setting for a digital camera has the same sensitivity to light as a 200 ISO film.

The ISO setting may also be called “film speed” and indicates the light gathering capacity of a digital sensor; the higher the ISO number the more light that is absorbed by the sensor. If the camera is set to an ISO setting of 100 the sensor will absorb little light, while at a setting of 1600 it will absorb a lot of light. The great advantage of the digital SLR camera is that the ISO setting can be changed for each photograph, whereas with a film camera the ISO setting is fixed for any roll of film.

The Olympus E520 has ISO numbers:

100     200     400     800     1600
        --->       increasing sensitivity to light

Each change in ISO setting will either increase or decrease the shutter speed by one full stop i.e. the amount of light reaching the sensor will either halve or double. A change in ISO from 200 to 400 will double the amount of light that will reach the sensor (and the shutter speed can be halved for the same exposure); a change to ISO 100 will halve the amount of light reaching the sensor (and the shutter speed will need to be doubled to achieve the same exposure).

Unfortunately as the ISO setting is increased so will the digital ‘noise’ in each photograph. This makes the photograph look speckled rather than smooth. With film this is called ‘graining’. Noise also disrupts the clean line of an image so that it may appear slightly unfocussed.

The 2 images below are examples of 'noise', both being taken at ISO 1600.

Notice the 'graininess' at the top of the photo

Notice the lack of clarity and graininess of the squirrel's fur.



References:
Collins Complete Photography Course. John Garrett and Graeme Harrris. 2008. Harper Collins Publishers. ISBN: 978-0-00-727992-0
Get the most from your digital SLR. The Digital SLR Guide. Chris Roberts. 2008. Downloaded from the Internet March 2009.

Shutter Speed

What is Shutter Speed?

Shutter speed is the amount of time that the shutter stays open.

The shutter is located in the camera just in front of the sensor and consists of two separate curtains – as the shutter release button is pressed one curtain opens to expose the sensor to light, followed by the second curtain closing to block the light.

Most shutter speeds are measured in fractions of a second – so a shutter speed of 60 means that the shutter remains open for 1/60^th of a second. Thus the smaller the number the longer the shutter remains open – the slower the shutter speed.

The fastest shutter speed of the Olympus E520 is 1/4000^th of a second.

4000  2000  1000  500  250  125  60  30  15  8  4  2  1

 Very fast                                                        slow

1/4000^th sec                          1/125^th sec                 ¼ sec

The shutter speed settings are in steps each of which halves or doubles the length of time the shutter remains open – or the exposure time of the sensor to light.

A change in shutter speed from 250 to 125 (or 1/250^th second to 1/125^th second) doubles the exposure time; whereas changing the shutter speed to 500 (1/250^th second to 1/500^th second) halves the exposure time.

Shutter speeds can be longer than 1 second; the annotation for these is that the speed is followed by a quote mark “. Thus a shutter speed of 2 seconds is displayed as 2”.

The Olympus E520 can have a shutter sped as slow as 60 seconds (60”).

There is also a shutter speed setting called ‘bulb’. In this mode the shutter release is pressed once to open the shutter and a second time to close the shutter. The amount of time the shutter remains open is determined by the operator. With this setting movement can be tracked e.g. stars in the sky, car lights on a road.

Shutter speed and motion.

Shutter speed has a direct effect upon the recording of motion within a photograph.  An image in motion will be frozen at a fast shutter speed, whereas the same image taken at a slower speed will probably be blurred.

I plan to take photos within my garden of birds and animals whose movement is not only fast but also unpredictable – for this I will need to use a fast shutter speed. I also plan to take photos of plants and trees which might be quite still so a slower shutter speed can be used – but even leaves blowing in a gentle breeze can be blurred with a slow shutter speed.

Shutter speed and the hand held camera.

When holding a camera in your hands a very slow shutter speed will cause blurring of the whole image. If using a shutter speed of 4 (1/4 second) the shutter remains open for a relatively long time with the effect that camera shake will cause blurring. For this situation the use of a tripod to stabilise the camera and prevent camera shake is essential.

Shutter speed and focal length.

Focal length is the measurement in millimetres from the optical centre of the lens to the camera’s sensor.

If a camera is hand held (without use of flash) using a shutter speed slower than the reciprocal of the focal length will result in a blurred image.

Focal length	1/focal length	Closest shutter speed
28mm	1/28	1/30th second
50mm	1/50	1/50th second
100mm	1/100	1/100th second
300mm	1/300	1/320th second

The Olympus E520 contains an image stabilisation system. Image stabilisation will to a certain extent counteract the movement of the hand held camera. This means that shutter speeds slower than the reciprocal of the focal length can be used without blurring – but only for stationary objects.

The table above becomes:

Focal length	1/focal length	Closest shutter speed
28mm	1/28	1/15th second
50mm	1/50	1/30th second
100mm	1/100	1/50th second
300mm	1/300	1/160th second

References:
Collins Complete Photography Course. John Garrett and Graeme Harrris. 2008. Harper Collins Publishers. ISBN: 978-0-00-727992-0
Get the most from your digital SLR. The Digital SLR Guide. Chris Roberts. 2008. Downloaded from the Internet March 2009.

Aperture

What is aperture?

Aperture is the width of the opening in the camera lens.

The camera lens contains an iris diaphragm constructed of metal leaves that open and close to give a smaller or larger opening through which light enters the camera to reach the sensor.

It is can be compared to the iris of the human eye: when it is very sunny the pupils (lens) constrict to limit the amount of light reaching the retina (sensor); in the dark of night the pupil will dilate to increase the amount of light reaching the retina.

Aperture size is measured in f-stops, with the smallest f stop of the lens having the largest aperture (or opening) and the highest number being the smallest aperture. The reason for this is that f stops are measured in fractions:

 f-stop             =                                  focal length of the lens                  

                                                diameter measurement of the aperture

The common scale for apertures is:

1.4       2.0       2.8       4.0       5.6       8.0       11        16        22        32

wide open                                                                              very narrow

            f/2.8                                        f/8.0                            f/22

With each value quoted above the aperture size either halves or doubles. A change in f-stop from 4.0 to 5.6 will halve the aperture size and hence the amount of light reaching the sensor, whereas changing from 4.0 to 2.8 will double the aperture size.

In addition the Olympus E520 uses third-stop increments;

4.0       4.5       5.0       5.6       6.3       7.1       8.0       9.0       10        11        13        14        16

This allows more flexibility in aperture size, but the relationship between the f-stop numbers remains constant.

The 14-42mm Zuiko lens for the Olympus E520 camera has a maximum aperture of f/3.5 down to a minimum aperture of f/22. However since this lens has a variable focal length (14 up to 42 mm) the lowest f-stop value increases as the focal length increases. (f/ 3.5 at 14mm; f/5.6 at 42mm). Thus when the lens is fully extended the maximum aperture decreases (f-stop increases).

f-stop values are specific for individual lenses. The low values of 1.4 or 2.0 are generally only obtained with the most expensive lenses.

References:
Collins Complete Photography Course. John Garrett and Graeme Harrris. 2008. Harper Collins Publishers. ISBN: 978-0-00-727992-0
Get the most from your digital SLR. The Digital SLR Guide. Chris Roberts. 2008. Downloaded from the Internet March 2009.