ISO

ISO 1600, f16, 30sec
ISO 3200, f16, 20sec

ISO 6400, f16, 10 sec
ISO stands for International Standards Organisation. Changing the ISO rating alters the strength of the signal passing through the sensor. The ISO rating, along with the shutter speed and aperture, plays a vital part in how the exposure is calculated. All three are linked together, so changing one has a bearing on the others.
Changing the ISO works in much the same way as that of shutter speeds and apertures. Going up a full stop (100 – 200) halves the exposure, while going down a stop (800 -400) doubles the exposure. The lower the ISO the less sensitive the sensor is to light and the more light is required to give the correct exposure, through a longer exposure time and/or wider aperture. Increasing the ISO boosts the signal travelling through the sensor and effectively increases the sensitivity, meaning that a faster shutter speed and/or smaller aperture gives the correct exposure.

To see my experimental images click here

These photos were taken at Darley park and these simply explain by just changing the ISO and keeping the aperture and shutter speed the same that the lower the ISO number the less sensitive the sensor is to light and the photo can be under exposed. The higher the ISO number the more sensitive the sensor is to light and the photo can become over exposed. That is just the basics to ISO's. If you were for example to take a picture of a mountain biker on a bright day and wanted to freeze the action you would use a high ISO to increase the sensors sensitivity to light along with a wide aperture to compensate for a fast shutter speed (to freeze action) which equals a short exposure time. The complete opposite is used to show movement in objects like water or a windmill turning. A low ISO along with a narrower aperture and a long shutter speed.

I have demonstrated this using a little bit of my initiative as I don't have a tripod or any other fancy equipment to be able to take photos with a slow shutter speed. So I turned on my kitchen tap balanced my camera on the kitchen side and took photos of the running water using a low ISO with a slow shutter speed and a high ISO with a fast shutter speed and also having to adjust aperture to try and get the best exposure. Click here to see these. The photos with the fast shutter speeds, freeze the movement of the water and gives the water texture also these photos I think are under exposed and I may of needed to use a flash to get a better exposure, the slower shutter speeds give the water a smooth effect and the pictures are better exposed.

Shutter speed

Shutter speed allows you to control whether to freeze its motion by selecting a fast shutter speed, or record it as a blur or a streak by selecting a longer shutter speed.
To keep an image sharp whilst holding the camera, a faster shutter speed is needed. The exact shutter speed is not a constant – it is largely dependant on the lens setting used.
Freezing movement; shutter speed plays an important part in capturing a moving object into a still image. The less time a shutter is open, the less the subject will move within the frame and the sharper it will appear. There are also other factors to consider, firstly the actual speed of the subject does not necessarily indicate how fast the image will change in the view finder. If a subject is moving directly away or towards the camera the image will change more slowly than if it were moving across the frame, and a slower shutter speed will be required to freeze it. The size of the image is also important. E.g. a train on the horizon will not seem to move as fast as a flower swaying in the breeze right in front of the lens. The longer the lens setting and the closer you are to the subject the faster the shutter speed you need.
Using a slower shutter speed can create a different type of image. An artistic approach to moving subjects is to use a slower shutter speed which suggests movement and action. Also using a slower shutter speed to capture moving lights such as fireworks will give a very artistic image.

I experimented in the studio with shutter speeds. I used ISO 200 for all images and the aperture ranges from 9-14 and the shutter speeds range from 2-6 secs. To see images click here. The first three images I tried changing the shutter speed but with the set up I had in the studio which was one Bowens 1000 with a spill kill/open disk reflector attached to it, it didn't work. What I wanted to try and capture was the movement of the ball but the flash prohibited this. The flash would fire when the shutter was pressed but the light wasn't constant. The shot of light froze the movement and the constant dim light from the flash unit once fired showed some movement of the ball. It was suggested by Steve that I was to use the bulb setting on the camera (which are the rest of the images) where the flash unit is set off manually and the shutter button depressed for the amount of time wanted. To get two points of movement the flash is to be set off twice and the shutter button released after the second flash, the same for three points of movement but the flash to be set off three times. For these set of images I set the camera to ISO 200 and used an aperture of 9 or 14 with a shutter speed of 2-6 secs. Although it was very difficult to try and catch the ball in the dark and so some of the facial expressions are quite comical I think it shows shutter speed and the use of studio lighting very well.

Aperture

Aperture is used in portraiture to control depth of field and determine how much of the scene appears sharp. For portraits a wide aperture can be used so the background behind the subject is thrown out of focus. (ie. F3.5 – 4.5)
The amount of depth of field is not a constant – it depends on three main factors; the aperture, the focused distance, and the actual focal length of the lens.
The size of the aperture used is the most important factor in the control of depth of field. Making the aperture smaller increases depth of field, while widening restricts it.
The distance to the subject also has an effect. At close distances, all lenses offer less depth of field than when they are focused further away.
The focal length of the lens affects the range of distances that appear sharp. The amount of depth of field dramatically reduces as focal length lengthens.

Click here to see a few more experimental images

I took some pictures of beer bottles to try and explain aperture. I focused on certain bottles to get different depths of field. I found that if I focused on the first bottle the rest gradually became more unfocused and vise versa if I focused on the last bottle the the ones closer to the camera were more out of focus. I sat quite close to them and used the zoom on my camera so that it would make more of a noticeable difference. If I sat further away and used less zoom there wasn't as noticeable difference in the depth of field shown here. I used aperture 4.5 and 5.6 on all of the photos and altered the ISO and shutter speed to get the right exposure. I started off with aperture 4.5 on ISO 200 with a shutter speed of 1/250 which made the picture too dark so I increased the ISO to 400 kept the aperture the same and used a slower shutter speed of 1/125 which gave a good exposure. The following images were taken with an aperture of 5.6 and ISO 800 and to get the best exposure the shutter speed was set at around 1/200.