Sunday, August 19, 2012

Motion Blur


Motion-Blur

Capturing movement in images is something that many of us photographers only think to do when we are photographing sports or other fast moving subjects.
While there are many opportunities in sports photography that emphasize the movement of the participants – almost every type of photography can benefit from the emphasis of movement in a shot – even when the movement is small, or very  slow .
Here are some tips for capturing movement:
1. Slow Down Your Shutter Speed
The reason for movement blur is the amount of time that the shutter of a camera is open long enough to allow your camera’s image sensor to ‘see’ the movement of your subject.
So the number one tip in capturing movement in an image is to select a longer shutter speed.
If your shutter speed is fast (1/2000th of a second or faster) you’re not going to see much movement (unless the subject is moving very fast) while if you select a longer shutter speed (5 seconds or so) you don’t need your subject to move very much at all before you start to see blur.
How long should your shutter speed be? – Of course the speed of your subject comes into play. A moving snail and a fast moving car will give you very different results at the same shutter speed.
The other factor that comes into play in determining shutter speed is how much light there is in the scene you are photographing. A longer shutter speed lets more light into your camera and runs the risk of blowing out or overexposing your shot.
 We’ll cover some ways to let less light in and give you the option to have longer shutter speeds below.
So how long should your shutter speed be to get movement blur in your shot? There is no ‘answer’ for this question as it will obviously vary a lot depending upon the speed of your subject, how much blur you want to capture and how well lit the subject is. The key is to experiment, using you’re digital camera is ideal as you can take as many shots as you like without it costing you anything.

2. Secure Your Camera
There are two ways to get a feeling of movement in your images – have your subject move or have your camera move (or both).
In this type of shot you need to do everything that you can to keep your camera perfectly still or in addition to the blur from the subject you’ll find that the whole frame looks like it’s moving as a result of using a longer shutter speed. Whether it is by using a tripod or have your camera sitting on some other still object (consider a shutter release cable or using the self-timer) you’ll want to ensure that camera is perfectly still.

3. Shutter Priority Mode
One of the most important settings in photographing an image which emphasizes movement is the shutter speed (as outlined above). Even small changes in shutter speed will have a big impact upon your shot – so you want to shoot in a mode that gives you full control over it.

This means either switching your camera into full Manual Mode or Shutter Priority Mode. Shutter Priority Mode is a mode that allows you to set your shutter speed and where the camera chooses other settings (like Aperture) to ensure the shot is well exposed. It’s a very handy mode to play with as it ensures you get the movement effect that you’re after but also generally well exposed shots.
The other option is to go with Manual mode if you feel more confident in getting the aperture/shutter speed balance right.
How to Compensate for Long Shutter Speeds When there is too much light
As mentioned above one of the effects of using longer exposure times (slow shutter speeds) is that more light will get into your camera. Unless you compensate for this in some way, this will lead to over exposed shots.
Below I have suggested the three main methods for making this compensation (note – a fourth method is simply to wait for the light to change (wait for it to get darker). This is why many shots that incorporate blur are taken at night or at dawn/dusk):
1. Small Apertures
How do you cut down the amount of light that gets into your camera to help compensate for a longer shutter speed? What about changing the size of the hole that the light comes in through. This is called adjusting your camera’s Aperture.
If you shoot in shutter priority mode the camera will do this automatically for you – but if you’re in manual mode you’ll need to decrease your Aperture in a proportional amount to the amount that you lengthen the shutter speed.
This isn’t as hard as you might think because shutter speed and aperture settings are organized in ‘stops’. As you decrease shutter speed by a ‘stop’ you double the amount of time the shutter is open (e.g. – from 1/250 to 1/125). The same is true with Aperture settings – as you decrease the Aperture by one stop you decrease the size of the shutter opening by 50%. This is great because an adjustment of 1 stop in one means that you just need to adjust the other by 1 stop too and you’ll still get good exposure.
2. Lower Your ISO
Another way to compensate for the extra light that a longer shutter speed lets into your camera is to adjust the ISO setting of your camera. ISO impacts the sensitivity of your digital camera’s image sensor. A higher number will make it more sensitive to light and a lower number will make the sensor less sensitive. Choose a low number and you’ll find yourself able to choose longer shutter speeds.
3. Try a Neutral Density Filter
These filters cut down the light passing through your lens and into your camera which in turn allows you to use a slower shutter speed.
It is sort of like putting sunglasses on your camera (in fact some people actually have been known to use sunglasses when they didn’t have an ND filter handy).
For instance, if you’re shooting a landscape in a brightly lit situation but want a shutter speed of a second or more you could well end up with a very over exposed image. A ND filter can be very helpful in slowing the shutter speed down enough to still get a well-balanced shot.
It is the use of ND filters that enabled some of the shots in our previous post to get a lot of motion blur while being taken in daylight.
Another type of filter that can have a similar impact is a polarizing filter. Keep in mind however that polarizers not only cut out some light but they can impact the look of your image in other ways (e.g. cut out reflection and even change the colour of the sky – this may or may not be the look you’re after).
Two techniques to try – one technique to experiment with if you’re wanting to capture images with motion blur is to experiment with Slow Sync Flash. This combines longer shutter speeds with the use of a flash so that elements in the shot are frozen still while others are blurry. Read more about Slow Sync Flash. Another technique worth trying out is panning – moving your camera along with a moving subject so that they come out nicely in focus but the background blurs.

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