Using full manual mode on your DSLR camera can seem like a daunting prospect. In this mode, the camera gives the user full control of all settings, and there can be a fair amount to remember.
Let's look at the three key components of using manual mode.
Aperture controls the amount of light that enters the camera through the iris in the lens. These amounts are represented by "f-stops," and a large aperture is represented by a smaller number. So, for instance, f2 is a large aperture and f22 is a small aperture. Learning about aperture is an important aspect of advanced photography.
However, aperture also controls depth of field. Depth of field refers to how much of the image surrounding and behind the subject is in focus. A small depth of field is represented by a small number, so f2 would give a photographer a small depth of field, while f22 would give a large depth of field.
Depth of field is extremely important in photography, and it should be one of the first things that a photographer considers when composing a photograph. For instance, a beautiful landscape shot won't be quite so pretty if a very small depth of field is accidently used!
Shutter speed controls the amount of light entering your camera through its mirror -- i.e., through the hole in the camera, as opposed to the lens.
DSLRs allow users to set the shutter speed from settings of around 1/4000th of a second through about 30 seconds ... and on some models "Bulb," which allows the photographer to keep the shutter open for as long as they choose.
These are obviously just a couple of examples. However, slower shutter speeds mean that photographers won't be able to hand hold their cameras and will need to use a tripod. It's widely accepted that 1/60th of a second is the slowest speed at which it's possible to hand hold.
So, a fast shutter speed only allows a small amount of light into the camera, while a slow shutter speed allows a lot of light into the camera.
ISO refers to the camera's sensitivity to light, and it has its origins in film photography, where different speeds of film had different sensitivities.
ISO settings on digital cameras typically range from 100 to 6400. Higher ISO settings allow more light into the camera, and they allow the user to shoot in low light situations. But the trade-off is that, at higher ISOs, the image will start to show noticeable noise and grain.
ISO should always be the last thing that you change, because noise is just undesireable! Leave your ISO on its lowest setting as a default.
Putting Everything Together
So, with all these things to remember, why shoot in manual mode at all?
Well, it's usually for all of the reasons mentioned above -- you want to have control over your depth of field because you're shooting a landscape, or you want to freeze action, or you don't want noise in your image. And those are just a few examples.
As you become a more advanced photographer, you will want to have control over your camera. DSLRs are brilliantly clever, but they don't always know what you're trying to photograph. Their primary objective is to get enough light into the image, and they don't always know what it is you're trying to achieve from your photo.
So, here's the trade-off to remember: If you are letting a lot of light into your camera with your aperture, for instance, you'll need a faster shutter speed and a low ISO, so that your image isn't over-exposed. Or, if you use a slow shutter speed, you'll likely need a smaller aperture as the shutter will be letting plenty of light into the camera. Once you have the general idea, you can easily figure out the various settings you need to use.
What settings you'll actually need will also depend on how much available light there is. For instance, I live in the U.K, where the weather is generally pretty gray, and I often struggle to get enough light into my camera. In direct contrast, when I lived in Africa, I often had to watch out for over-exposure, and using a small depth of field (and therefore a large aperture) could sometimes be a real challenge! There are no absolutes with settings, unfortunately.
Achieving the Correct Exposure
Fortunately, knowing whether you have the correct exposure is not completely reliant on guesswork. All DSLRs have metering and an exposure level indicator. This will be represented both in the viewfinder, and either on the camera's LCD screen or the external information screen (depending on what make and model of DSLR you have). You'll recognize it as a line with the numbers -2 (or -3) to +2 (or +3) running across it.
The numbers represent f-stops, and there are indentations on the line set in thirds of a stop. When you've set your shutter speed, aperture, and ISO to what you require, press the shutter button halfway and look at this line. If it's reading a negative number, it means your shot will be under-exposed, and a positive number means over-exposure. The goal is to achieve a "zero" measurement, although I tend not to worry if it's one-third of a stop over or under this, as photography is subjective to your own eye.
So, if your shot is going to be vastly under-exposed, for instance, you'll need to let some more light into your shot. Depending on the subject of your image, you can then decide whether to adjust your aperture or shutter speed ... or, as a last resort, your ISO.
Follow all of these tips, and you will soon have full manual mode under control!