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.
Although the shutter speeds and apertures are interchangeable as far as exposure is concerned, double the time the shutter is open and halve the size of the lens aperture to get the same exposure, 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 on the next page.
An Explanation of Shutter Speed
Shutter Speed refers to the amount of time the shutter is open. This is usually measured in fractions of a second, a 'normal' (hate that word!) shutter speed would be around 1/125th of a second with a standard lens or mid-range zoom lens on the camera. Unless you have extremely shaky hands, that will give you a sharp picture most of the time.
The shorter the time that the shutter is open the sharper the photo will be. If you are taking fast moving objects such as cars, cyclists or people running you need to select fast shutter speeds to capture the sharpest picture you can.
Panning the Camera
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 sharp and blur the background, so a careful selection of the right shutter speed to do both is necessary. You will 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 look very attarctive, it can also get you out of trouble when there is a lot of background 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.
You also need a steady hand of course and, as with everything else in life, practice makes perfect. When I took the picture above, we had a 'tame' cyclist who was willing to ride past us as many times as we wanted. I started with a 'safe' shutter speed of around 1/180th of a second and, as I got more confident, gradaully worked my way down to 1/45th of a second to increase the background blur as much as possible while still keeping the head and torso of the rider sharp. I think you'll agree that the picture does give you a good sensation of speed.
Zoom in on your Camera Screen to Check the Focus of your Shot
After you have taken the picture, if you have a zoom facility on your camera screen, now is the time to get familiar with it. I had my digital camera for quite a while before I realized that, while reviewing my pictures, I could zoom in to check the sharpness. Now I use it all the time. Zoom right in as far as you can then move the view around (normally by using the four arrow buttons) to check that the important bits of the picture are really sharp. It's much better to do this while you have the opportunity to take another picture than to wait until you get home and it's too late.
It's not only moving objects that 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. blur due to 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 did it on purpose :-).
Tip - When the shutter speed is important, as with fast-moving objects, it's a good idea to set the camera to 'Shutter Speed Priority' mode, usually designated by a Tv symbol. This is where you select the shutter speed and the camera selects the appropriate aperture according to the light reading.
Use a tripod when Shooting at Slow Shutter Speeds
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. See the photo 'Boulevard du Temple' on this page.
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.
Two Different Shutter Speeds
Finally here are two photos of the same fountain shot at different shutter speeds. The top picture was taken at a fairly fast speed, about 1/500th of a second and has frozen the drops of water in mid air.
The bottom photo was taken using a slower shutter speed, in other words the shutter was open for a longer time, which has allowed the fast moving water to blur a little. I don't remember what the shutter speed setting was for this shot but I would guess it was about 1/30th of a second because the camera was handheld and the bowl is quite sharp. At shutter speeds slower than 1/30th of a second it is quite difficult to hold the camera steady enough to get a sharp image. You need to use a tripod as I said above. The bowl of the fountain remains more or less the same in both photos because it did not move.
At the risk of labouring the point, i'd like to say again that whilst adjusting the shutter speed you need to adjust the aperture in the opposite direction to ensure that the same amount of exposure is given to the shot. If you use the 'shutter speed priority', Tv, setting on your camera this will be done automatically for you.
Getting away from the auto settings.
An explanation of the mechanics of exposure and the side effects of choosing different aperture/shutter speed combinations.
Overriding the automatic metering system.
What they are trying to tell you.
Setting up your camera to take a series of pictures at different exposures.
Another piece of the exposure puzzle.
An explanation, strictly for the jargon heads.
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