A beginner's guide to shutter speeds
This week: Our friend Ian wants to know about Shutter Speeds
Shutter speed? What’s that all about then? Well, one way in which you can take control of the exposure is to change the amount of time the camera’s image sensor is exposed to the light. You do this by adjusting how quickly the shutter opens and closes - hence the phrase shutter speed. No, you’ve lost me. What’s a shutter? Now we are getting into the mechanics of how your camera works. On most cameras there is a pair of metal blades that cover the image sensor. Like curtains, these block out the light until you are ready to take the image. When you press the button to take a photo (also known as the ‘shutter button’) the shutters open and lets the light in for a brief time, then close again, ending the exposure time. It’s the shutter speed that sets how long the sensor is exposed. So what shutter setting should I use? If you are using one of the fully automatic modes (e.g. AUTO or Program (P) mode), the camera will decide what shutter speed to use based on what it thinks you are trying to do but that’s not always the best one to achieve the look you want, particularly if there’s a moving subject in the shot. Your camera might also have an automatic sports ‘scene’ mode (typically shown as a little running stick man icon) which will set a relatively fast shutter speed to try and freeze the action but again, that’s letting the camera make the choice for you. As you take more control of your camera, the two modes that let you choose and set the Shutter Mode are the fully manual (M) mode or the semi-automatic shutter priority (S) mode. All you Canon owners wondering where the S mode is, it’s called Time value (Tv) mode – nothing like standardisation, eh? Once you’ve turned the mode dial to your chosen setting you can then adjust the shutter speed by turning the exposure dial – this can range from 30 seconds to 1/4000th of a second or faster, depending on your camera.
Can’t I just set a shutter speed and leave it? Unfortunately it doesn’t quite work like that. Not only does your shutter speed depend on the amount of light available, it also depends on whether the subject is moving or not. As shutter speeds get longer in duration, there’s more opportunity for your subject to move during the shot which leads to motion blur. The image below is of a slow moving ‘light sculpture’ – it’s not a matter of right or wrong, more that the choice of shutter speed really alters the effect achieved with the photo.
Well, tell me what to use then…
It really does depend on the amount of available light, you camera and lens and the type of effect you are trying to achieve. Judging the correct shutter speed for a given situation is something you only really learn from experience. You should really experiment, perhaps try different shutter speeds on still and moving subjects and see what effect it has on…
JUST TELL ME!
OK, OK. The following are really no more than a rough guide for a series of typical subjects. Do be aware that other facts like the type of lens used (e.g. a wide angle, portrait or telephoto) can have a big effect on how easy it is to freeze or blur a subject – as a rule of thumb, the longer the focal length, the easier it is to blur motion, whether its desired or not!
Right, got that… anything else I should know? Well, freezing subject motion is important but there’s also hand shake / camera shake to consider – basically the slower the shutter speed, the more likely that YOU will cause the camera to move slightly during the shot. You might think you are perfectly still but even just pressing the shutter button slightly which can be enough to shake the camera, blurring the shot! By using a higher shutter speed you can minimise this. It’s a particularly a problem when using a telephoto zoom lens (e.g. a 200mm telephoto) as zooming into you subject amplifies small camera shakes. As a general rule, a shutter speed of 1 divided by the focal length of your lens times your cameras crop factor minimises camera shake effects. If you have an aps-c or non-pro digital DSLR camera, your crop factor is typically 1.5x (Sony, Nikon) or 1.6x (Canon). So, for a Sony crop camera with a 50mm lens, a suitable shutter speed would be 1 divided by (50 time 1.5) or 1/75th of a second. For a 200mm lens that becomes 1/300th of a second (or 1/(200x1.5)). As a rough guide you can roudn these numbers up or down depending on what shutter speeds are selectable on your camera. Using our Sony 1.5x APS-C crop camera as an example;
OK...shaky hands = bad Yes but fortunately we have stabilisation technology! many lenses and cameras also have a feature to stabilise the lens to avoid this type of camera shake called shake reduction (SR), vibration reduction (VR), steady shot (SS) or Optical image stabilisation (OIS) etc depending on your camera brand. Basically the camera senses your slight camera shake and very quickly moves the lens or sensor in the opposite direction to compensate for the shake effect. The technology has advance a lot in recent years so whilst an unstabilised 200mm lens might require 1/300th of a second to avoid camera shake, with stabilisation getting shake-free hand held shots at shutter speeds as slow as 1/30th of a second is quite achievable. Just be sure to check that your lens / camera has stabilisation and that it’s switched on (usually a switch on the lens itself or an option in the cameras shooting or function menu). You can minimise camera shake by holding your camera and supporting your lens securely and bracing yourself by leaning against something solid like a wall. Or you can use a sturdy tripod and shutter remote to avoid hand shake or even touching the camera whilst taking a photo – if you don’t own a remote you can still use the self-timer built into you camera to avoid that shutter button shake effect. However, as great as image stabilisation and tripods are for avoiding camera shake… they have ZERO effect on how you freeze the motion of a subject! Don’t assume that just because you can hand hold your telephoto lens at 1/30th of a second without camera shake or stick your camera on a tripod that you can freeze a bird in flight at such a slow shutter speed. Also, using stabilisation and very high shutter speeds or stabilisation and a tripod at the same time can occasionally CAUSE image blur as the stabilisation tries to over compensate for tiny or absent camera shakes so do check your settings if you get unexplained camera shake effects under these circumstances.
OK… is that it then? Well, it’s actually quite important to understand how to balance shutter speeds, ISO and apertures – we often refer to this balance as the EXPOSURE TRIANGLE – but that’s a blog in itself! Maybe we’ll get to that in a few weeks’ time.
The opinions in this blog are solely those of the Photo Doctor and do not necessarily reflect those of Medway DSLR camera club or any member of the committee. In fact the Photo Doctor constantly argues about technical stuff with them. They normally give in and admit he's right in the end...