Shutter Speeds and Apertures

Depth of Field explained. Panning at slow shutter speeds. Blurred pictures. Selective focus. Blur the background. Tricks and tips for working with shutter speeds and apertures.

Shutter Speed

Although, as discussed in exposure, the shutter speeds and apertures are interchangeable as far as exposure is concerned, they each have their own unique effect on the picture. Let's take a look at shutter speeds first as their effect is easily understood. We'll look at apertures further down the page.

The shorter the time that the shutter is open the sharper the photo will be.

If you are photographing fast moving objects such as cars or people running you need to select fast shutter speeds to capture the sharpest picture you can. One exception to this is when you are panning the camera with the subject, the object of the exercise here is to render the subject sharply and blur the background, so a careful selection of the right shutter speed to do both is necessary. I often find that a little blur in the right places on a picture gives a greater sense of movement than if everything is pin sharp. This blur, however, must be in the right places, normally we want to see the head and torso rendered sharply but, if the feet and hands are blurred, it can often be a good thing. Blurring the background can also get you out of trouble when there is a lot of clutter that will detract from the main subject. Getting the shutter speed right to render the correct balance of sharpness and blur on any given subject can really only be determined through trial and error. One of the great advantages of the digital camera with it's instant playback is that this learning process can be a lot shorter than it was before. If you have a zoom facility on your playback of pictures, now is the time to get familiar with it. I had my digital camera for quite a while before I realized that I could review my pictures and zoom in to check the sharpness.

Not only moving objects suffer from too slow a shutter speed. If you are holding the camera in your hand rather than having it mounted on a tripod, you will see the telltale signs of 'camera shake' (i.e. the movement of the camera) at shutter speeds longer than 1/125th of a second. A secure pair of hands will be able to get away with 1/60th or even 1/30th of a second but the camera would be better mounted on a tripod. Once again I will say at this point that the difference between a mistake and an effect is usually the degree. A small amount of blur would be considered a mistake, whereas really blurred streaks of light can be an interesting effect. It's all a question of convincing the viewer that you intended to do it.

Tip - When the shutter speed is important as with moving objects, it's a good idea to set the camera to 'Shutter Speed Priority' mode. This is where you select the shutter speed and the camera selects the appropriate aperture according to the light reading.

Of course, if you are taking photos of static objects like houses with a camera mounted on a sturdy tripod, you can leave the shutter open as long as you want without blurring. An interesting by-product of this, if you get to see really old photos taken in the first part of the 19th century, you will see that there are almost no people in the photos at all. That is because the exposure times were so long that the people had walked through the scene without being rendered. For the same reason the really early pictures, in the time of Niépce, the late 1830's, have almost no shadows because the plates took all day to expose and the sun moved across the sky illuminating the scene from both sides.

Apertures

As well as letting more or less light into the camera the size of the aperture you choose governs the 'Depth of Field'. Depth of field means the amount of the picture, from foreground to background, that is in sharp focus. A smaller aperture will give you a greater depth of field and a larger aperture will give you a more restricted depth of field. This characteristic can be used to good effect in many ways.

If you are photographing vast landscapes on a sunny day, the chances are that everything will be in focus and you will not notice this phenomenon at all. Depth of field, or the lack of it, is much more noticeable when taking close-ups. As I mentioned in the section on moving subjects, it is often desirable to render the background of your picture out of focus. This is easy to achieve by selecting a larger aperture to restrict the depth of field.

Conversely, when photographing very small objects (as in the picture opposite) getting everything in focus can be quite a challenge and may require a very slow shutter speed in order to be able to use the smallest aperture available. The focal length of the lens makes a difference to the depth of field available, the longer the lens the more restricted the depth of field. A wide angle lens will give you almost limitless depth of field.

Tip - If depth of field is important to either make sure everything is in focus or to throw some things out of focus, select the 'Aperture Priority' mode on your camera. In this mode you select the aperture and the camera selects the shutter speed according to the available light.

Tip - If you are shooting in bright light and want to restrict the depth of field, use a neutral density filter in front of the lens to reduce the light entering the lens. These are available in different densities, 2x, 4x, 8x etc. each one cutting the light in half, quarter, eighth etc. In extreme circumstances you can screw a couple of them together. Although they are 'neutral density' filters and should not effect the color balance, if you use two or more together you might need a little color correction at the printing stage.