September 14th, 2011
Most digital SLRs have four main modes which include, aperture priority (A or Av), shutter priority (S or Tv), program mode (P) and manual mode (M). There can be others as well but they tend to be automatic or scene selection modes where the camera makes all the decisions for you. For the purpose of this lesson I’ll just cover the four settings that leave some control to the user.
Program mode (P)
The cameras P mode is one step up from fully automatic it’s the one that everyone reaches for when they first start taking things a little more seriously. The camera still makes a lot of decisions for you but you do have some control over the final settings. In P mode you can still choose the ISO sensitivity of the sensor, the metering mode, the focusing points and the white balance. The aperture and shutter speed are all decided by the camera, however you have got the option to apply under or over-exposure using exposure compensation. You can also change the combinations of shutter and aperture settings that the camera chooses to create the same exposure, but the camera will always choose a combination to give what it thinks is the correct exposure based on the metering mode you have selected. This is where you can run into problems for one it can be time consuming constantly jogging through all the combinations and two the camera doesn’t always get it right.
Where I do find P mode useful is when I’m using a flash, flash photography can be particularly tricky to master and sometimes it’s easier just to leave the decision to the camera.
Shutter Priority (S or Tv)
Shutter priority is a partially manual mode, you select the shutter speed of the camera and the camera will automatically choose the aperture for you. The camera’s choice of aperture will depend on the metering mode the user selects to expose the scene. Basically the camera will select an aperture that it thinks will give a correct exposure based on the shutter speed selected by you. Shutter priority is great for situations where you want to have creative control over any motion in your photographs. To capture a fast moving object such as a motorbike or car you can select a fast shutter speed which will make sure you freeze the action without any motion blur, by doing this in shutter priority you only have to worry about the speed setting, the camera will take care of everything else. Alternatively by selecting a slow shutter speed you can choose to show some motion in a photograph such as the silky water you get in some landscape photographs. Slow shutter speeds are also used in night photography and for interesting lighting effects such as traffic trails and star trails.
Using a slow shutter speed allowed me to get the milky water effect in this landscape photograph
A fast shutter speed helps freeze action such as the horse jumping in this photo
Aperture Priority (P or Pv)
This is probably the mode that I use the most, it gives you control over the aperture of the camera which in turn gives you control over the depth of field. The depth of field is a great tool for photographers as it controls how much of an image is in focus and therefore has a huge impact on the final look of the photograph. The aperture is basically a diaphragm inside the cameras lens which opens and closes depending on the settings you select. The larger the aperture the smaller the depth of field (less in focus) and the smaller the aperture the larger the depth of field (more will be in focus). To confuse things a little bit a small aperture means a higher f number on the camera and a large aperture means a smaller f number. F-Number, also known as a focal ratio, is the ratio of the diameter of the lens aperture to the length of the lens. The more you open up the lens (smaller f number) the more light gets into the camera and so the faster the shutter speed you can use. If you close down the aperture (higher f number) you reduce the amount of light coming into the camera and so you will need a longer shutter speed to achieve the same exposure.
Enough technical stuff how does it work in practice? A good example of when to use a shallow depth of field (large aperture or small f number) would be in portrait photography when you want to isolate the subject from the background. By focusing on the your subject and choosing an aperture of say f4 or less you can keep the subject nicely in focus whilst throwing the background out of focus which will draw your attention to the subject.
For landscape work large depth of field can give you an image which is in focus from the from the foreground to the background creating a scene which is nice and sharp to look at. To successfully achieve this you could experiment using apertures of f 16 or greater and focus about 1/3 of the way into the scene you want to capture. For more information on this you can google hyperfocal distance, I won’t get into that here but it is worth looking up if you want to find out more about what is going on.
The reason I find aperture priority the most useful setting is because a lot of the time it is the depth of field that want to control in my photographs and with modern metering systems I find the camera more often than not gets the exposure right without me having to worry about the shutter speed. There are times when the camera doesn’t always get it right and this is when I would switch to manual mode.
Large apertures (low f number) help isolate your subjects from the background creating a shallow depth of field.
Scenes like this can be captured using a small aperture (high f number) to create a large depth of field keeping everything sharp from front to back.
Manual Mode (M)
This is the mode that most beginners stay well clear of but actually it’s not that scary. In this mode you have control over all the settings of the camera, the camera makes no decisions for you, so if you take a photo that’s under or overexposed it’s all your own fault!! So how do you know when the exposure it correct? That’s easy you use can either use the cameras built in meter or you can use a handheld light meter. Most of the time you will probably use the camera’s meter and to do this you just need to adjust the shutter speed and aperture setting until the meter shows the correct exposure. The exposure meter can be seen through the viewfinder of the camera and shows a scale from –2 to +2 with 0 in the middle, the 0 is where the camera thinks the correct exposure should be. All you need to do is set the aperture and shutter speed until this scale is set at zero, anything above or below will overexpose or underexpose the image according to the cameras calculations.
So when would you want to use manual mode? When you set the camera in manual mode nothing changes unless you change it, so once a combination of shutter and aperture have been set the camera will continue to use these settings for all the photographs until you decide to change them. This is great for scenes where the lighting is fixed such as studio setups etc. It’s also great when the lighting can fool the cameras meter such as strong backlighting or high contrast scenes where the dynamic range of the camera is being stretched too far. For these scenes you can choose what part of the photograph should be correctly exposed and set the camera accordingly.
The great thing about digital photography is the immediate results you get, you have nothing to lose with trying things out and experimentation is the key. So next time you’re out, turn off that auto mode and try playing with some of the modes above and you’ll be amazed at how much more creative you can be when you’re the one making the decisions!