When’s it best to use the Tv mode on your Canon D-SLR?
Fast track your photography skills with our crash course in setting shutter speeds.
Why is the shutter speed so important?
While the aperture value controls the amount of light your camera’s sensor receives, the shutter speed determines how long the sensor is exposed to light. Exposure time is usually measured in fractions of a second (1/250 sec, for example), but it can be up to several minutes, depending on the light levels, choice of aperture and ISO setting (a measure of how sensitive to light the sensor is). As well as ensuring that the sensor receives enough light to make a good exposure, the shutter speed affects how movement, of both the subject and the camera, is captured. Fast speeds, such as 1/2000 sec, can be used to freeze fast-moving subjects, while at slower speeds – 1/2 sec, say – anything moving during the exposure will appear blurred in the shot. And the whole picture will be blurred if the camera is moved during a slow exposure, however slight this movement – even a tenth of a second is a long time in exposure terms. So it’s important to keep an eye on the shutter speed in every shooting mode to make sure you capture sharp images.
Fast shutter speed – 1/1000 sec Slow shutter speed 1/100 sec Very slow shutter speed 1 sec
For freezing fast motion For panning your camera For artistic effects such as zoom blur
To take direct control of the shutter speed, you should switch your EOS to ‘Tv’ mode. Time Value (aka Shutter Priority) is a semi-auto exposure mode that enables you to dial in how long you want the exposure to be. This setting will be locked in, and the camera will select an appropriate aperture to make a standard exposure. Using this mode means you can react faster to situations than if you were shooting in full Manual mode, where you have to select both the shutter speed and the aperture. It’s for this reason that Tv mode is a great choice for photographing sports and action, whether it’s a football match or your kids playing in the park; you can choose a fast shutter speed to give you crisp shots, and let the camera open and close the aperture to compensate for changing light levels. If you used Av (Aperture Value) mode in this instance, you’d have no control over the shutter speed and you might end up with blurred results. For a similar reason you should try and avoid your camera’s Sports scene mode – you get zero input on the shutter speed, nor the ISO or the aperture. The camera tends to pick a very fast shutter speed and high ISO combination, which might not suit the conditions, or the effect you want.
Shutter speeds and panning
Panning is a popular technique for shooting sports, moving wildlife and other action as the motion blur captures a sense of movement. You move your D-SLR at the same speed as the subject while you shoot. Because the subject stays (more or less) in the same position within the frame, they stay sharp, but the rest of the picture becomes blurred, as long as the shutter speed is slow enough. Choosing the shutter speed for panning all depends on how fast the subject is moving – and how good your D-SLR technique is! If the shutter speed is too fast for the subject then the background won’t be very blurred, if at all; if it’s too slow, you’ll end up with a very hazy frame – albeit one full of energy.
1/50 sec 1/800 sec 1/100 sec + flash
You can use a ‘blip’ of flash in combination with a slow shutter speed to get the best of both worlds: sharpness and blur. You’ll need to be close to your subject to do this with your camera’s built-in flash, though.
Finding the ‘right’ speed
How do you decide which is the ‘right’ shutter speed for a moving subject? Well, it’s both a technical and a creative decision. Technically, you need to take into account the subject’s speed, direction of movement and their size in the frame. A close-up subject requires a faster shutter speed than a distant one moving at the same speed, as it moves a proportionally greater distance across the frame during the exposure; for the same reason, subjects moving across the frame need a shorter exposure than those moving towards or away from you. Speed’s the biggest consideration: a car travelling at 100mph, for instance, will need a faster shutter speed to freeze its movement than one travelling at 30mph. The creative decision in all this? You need to decide if you should forget sharpness and ‘embrace the blur’ by using a slower shutter speed. The results can be unpredictable, but can also be aesthetically pleasing.
1/40 sec 1/10 sec 1/5 sec 0.8 sec
STEP BY STEP - Avoid underexposure in Tv mode
You need to keep an eye on the aperture value in Tv mode, especially when you’re shooting at fast speeds.
1. Lens choice
Choose your ‘fastest’ lens if you’re shooting action. The maximum aperture is indicated on the front of the lens – this lens changes from f/3.5 to f/5.6 as it’s zoomed.
2. Select the speed
Select Tv on the mode dial, then use the main dial to set the shutter speed, or press the Q button and set the shutter speed on the Quick Control Screen. We chose 1/1000 sec.
3. Aperture alert!
A len’s aperture range is fixed. If the camera can’t select a wide enough aperture to match a fast shutter speed, the aperture value flashes on the LCD screen and in the viewfinder.
4. ISO to suit
To avoid this picture being underexposed, we need to increase the ISO value. We chose ISO800, making the sensor three times more sensitive to the limited amount of light.
Stopping the shakes
Blurred photos are often caused by the shutter speed being too slow for you to hold the camera steady during the exposure. Using a tripod solves this, but even then you need to use good technique, such as firing the camera with a remote release. If you have no option but to shoot handheld, base the shutter speed on the focal length of the lens – so at 200mm, you’d need to dial in a shutter speed of at least 1/200 sec for sharp pictures. Image stabilized lenses let you shoot at slower speeds; the latest Canon 70-200mm f/2.8 gives you an extra four stops of ‘handholdability’.
A 400mm lens was used handheld at 1/40 sec, when it should have been 1/400 sec. The result is one soft shot!
This entry was posted on Tuesday, November 27th, 2012 at 12:06 pm and is filed under Canon D-SLRs. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a comment. Pinging is currently not allowed.