When shooting in manual there are 3 main settings which determine the outcome of your image. The ISO, aperture and shutter speed.
These setting can be very confusing when you first start using them instead of the “auto” mode or one of the built in underwater settings your camera has. Learning how to use these properly and understanding the relationship between them will make a big difference in the overall quality of your images.
The Shutter Speed indicates the speed in which the curtain opens then closes, and each shutter speed value also represents a “stop” of light. The shutter speed is measured in fractions of a second and affects the amount of ambient light entering the camera. A shutter speed of 1/60 means that the shutter is open for one sixtieth of a second. Cutting the shutter speed in half (in this case to 1/120 ) would increase the ambient light exposure by one stop which results in twice as much light getting in.
The Aperture controls the lens’ diaphragm, which controls the amount of light traveling through the lens to the film plane. The aperture setting is indicated by the f-number, whereas each f-number represents a “stop” of light. As you reduce the aperture, the F-stop increases in number (e.g. F8, F11, F16) and the amount of light that enters through the lens decreases. This can be a bit confusing but basically a small F-stop (e.g. – 2.8) is a large aperture – as the F-stop number gets larger (e.g. – F22), the aperture gets smaller. Decreasing the aperture by one “stop” will let in 50% less light.
In very basic terms, ISO is the level of sensitivity of your camera to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called “image sensor” or simply “sensor”. It is the most important (and most expensive) part of a camera and it is responsible for gathering light and transforming it into an image. With increased sensitivity, your camera sensor can capture images in low-light environments without having to use a flash. But higher sensitivity comes at an expense – it adds grain or “noise” to the pictures.
The graphic below can make it easier to understand. Each side of the triangle represents a component of the amount of light contributed to the overall exposure of a given scene. The longer the side of the triangle, the more light contributed. If you increase/decrease the length of one side of the triangle, you must equally increase/decrease, respectively, the length of another side, or split the length proportionally between the other two sides.
There are several websites I’ve used which have excellent articles explaining the relationship between these settings and how to use them to create the best effect.
www.uwphotographyguide.com is an excellent resource. An online book and magazine providing underwater photography tutorials full of useful tips and techniques by Scott Gietler.
www.backscatter.com is another great site with lots of articles, tutorials and underwater photography equipment for sale.
I’ve also used www.divephotoguide.com quite a bit. Lots of information and tutorials on different shooting techniques and there’s also a monthly underwater photography contest you can enter.
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