Cameras are stupid! Harsh thing to say, I know. Especially coming from someone whose business is based around cameras. But it's true, cameras are not intelligent. They struggle to make decisions on their own and they are limited as to what information they can ascertain about their surroundings. I've discussed the need to be able to white balance or shoot in RAW which comes from the inability of a camera to realise it is underwater and at a certain depth, in water of a particular tint and then automatically work out what the colours should look like.
The more control over the settings of your camera you have the more you can choose how your images appear. Many shots in underwater photography are unachievable with a camera set on automatic.
There are three primary settings that have a big impact on how your images appear.
ISO in basic terms is the sensitivity of the camera. The higher the ISO is set the less light the camera needs to produce an image, but as the ISO rises quality starts to decline. Depending on the sensor size and other issues some cameras will start to get noise in their images at lower ISO's than others. Increasing ISO allows you to adjust other settings which will reduce the amount of light reaching the sensor. Many cameras allow ISO to be adjusted in most of their modes apart from Auto.
Like all the settings discussed in this blog ISO can be used in land photography as well. To achieve the image of this lion taken on a dull South African winter's morning I raised ISO to 2000 to allow me to keep shutter speed high while using a camera with a long lens hand held.
Aperture is how wide the opening of the lens' iris is. This is denoted by an f number, the lower the number the wider the aperture. Camera lenses have stated minimum and maximum apertures. The wider the aperture can be the more light can reach the sensor, but also the shallower the depth of field. Depth of field decides how much of the foreground and background in an image will be in focus. Shallow depth of field can be used to isolated the subject and is one method for dealing with unattractive backgrounds that would otherwise detract from the image.
In the picture below, a wide aperture was used to give a shallow depth of field so that not much more than the eyes of this ribbon eel are in focus.
Thirdly Shutter Speed
Shutter speed is how long the shutter is open for when an image is taken. It is measured in seconds, usually as fractions but can be set to multiple seconds or even minutes in some cases. Adjusting shutter speed affects the exposure of an image taken using available light and also whether blur occurs from movement in the image. When using flash the shutter speed can be used to control the exposure of the areas of the image not lit by the flash. Using fast shutter speeds can give dark or black backgrounds to macro shots even in shallow water during the day.
This image of a scorpion fish was taken using one strobe with the cameras shutter speed as high as possible. In this case the camera was a mirrorless one and flash sync speed (the fastest shutter speed at which you can use the flash without getting shadow from the shutter curtain in your shots) was 1/160. With compact cameras that do not have mechanical shutters like mirrorless and DSLR cameras you can set shutter speed as high as the camera will go and still be able to use the flash. This makes it easier to achieve a black background (more on flash in the next instalment).
In wide angle shooting adjusting shutter speed is a good way of controlling what is visible in the background and the shades of blue or green in the water. The light from the flash will freeze the subject but with a slow shutter speed you will still get motion blur in front of or behind the subject depending on what curtain setting you have the flash on.
In the image below strobes were used to light the foreground while the shutter speed was adjusted to achieve the blue colour and surface effect in the water.
Hopefully you now have more idea how being able to adjust these settings yourself can improve your underwater images. Many cameras on the market that are sold with underwater housings or are waterproof don't allow you to adjust all these things independently. The very popular Olympus TG4's and 5's for example lack the ability to manually control shutter speed.
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