Of the many issues around fstop (aperture) and shutter speed, creative use of motion is one of the most interesting. Usually it is discussed with regard to achieving a pleasant but unnatural cream effect in flowing water, or in the opposite context, “freezing” fast motion.
Decreasing the amount of light that reaches the sensor/film can be achieved by using filters, using a slower film (or lower ISO setting) or by simply working where and when the light levels are naturally lower - indoors, in a rain forest, in the later part of the day. Reduced light levels are usually cited as a problem to be overcome, by using wider apertures and/or slower shutter speeds to achieve a proper exposure. In this Intel, we will be considering it an advantage because it allows slower shutter speeds.
If the available light requires a slower shutter speed, subject movement comes into play as a creative element in the photograph. In a studio, the lighting can be controlled to some extent, and you can simply slow down the shutter speed to whatever will give you the proper exposure and even zoom the lens during an exposure for special motion effects. In the outdoors, it will be wind or maybe water movement, or perhaps a running horse that provides the extra element. Before exploring long exposure, we need to look at two issues: reciprocity failure and noise.
Reciprocity Failure - Film photographers have to deal with a problem called reciprocity failure at long exposures. in this context, “long” can mean as little as 2 seconds. Reciprocity is the ideas that shutter speed and aperture are reciprocal values. If you double the shutter speed, and halve the aperture, the exposure stays the same: 1/50 at f16 is the same as 1/100 at f22. At very long speeds, this relationship breaks down - the reciprocity law fails. The result of this is that as film is exposed for a longer period of time, it becomes less sensitive to light, and even compensating with a wider aperture, the colour balance of the film shifts. This is a problem of the film, not of the camera.
Noise - Luckily, digital cameras don't have that problem as they can handle exposures of many seconds or longer without a shift in colour. However, digital cameras do have to deal with the problem of noise that inherently crops up as stray pixels during longer exposures. Noise is most obvious in regions of regular colour. You can see it in skin tones or on a wall in the background, for instance. How can you fix, or at least minimise, this problem
Minimising Noise in the Camera - The lower your ISO, the less noise you'll get in your photos. Therefore, if you are trying for slow shutter speeds, you are in luck, because in low light, that is what you will have.
Be sure to turn off your camera’s auto ISO setting and set the lower practical ISO yourself, otherwise, sensing low light levels, your system will boost ISO to the maximum; just what you don’t want!
If longer exposures still result in noise, check your camera's settings for a noise-reduction mode. Many digital cameras--especially models that support very high ISO levels--have a menu setting that reduces noise when the ISO is set at 800 or higher. It can be a good idea to turn this on at lower ISO, but do not take it for granted. All noise reduction systems reduce picture sharpness. Some are more “aggressive” than others in their efforts to reduce noise, and the result can be quite a severe loss of detail.
If you have the choice, use your RAW setting. If not, and you are less than thrilled by the noise reducing smear produced in your camera, turn it off and use the more powerful software in your computer to manage your noise problem.
Software Noise Reduction - Major image editors, including Corel's PaintShopPro and Adobe's Photoshop Elements, have noise-reduction tools. They have become remarkably effective in recent years, and in my experience, are now as good as the stand alone programs like Noise Ninja or Pure Image. If you do not have a good image editor (you should have!), then a stand alone is a good investment, if only because Pure Image, for instance, includes extra functions like Shadows and Highlights Level, (adjusts the shadows and highlights to give a dull image punch), Exposure Compensation (to fix exposure by bringing up details from shadows or tone down overexposed images), Colour Temperature Filter (adjusts image towards warmer or cooler tone and fix a colour cast from flash or wrong White Balance). and Colour Boost (to lift colours to make your image Vivid - this is NOT the same as a conventional saturation) - in other words, good noise software can substitute for some of the features of an standard image editor.
Motion - Capturing movement is standard practice if you are photographing sports or other fast moving subjects However, when it comes to creative photography, sometimes our goal is to emphasise movement rather than stop it - almost every type of photography can benefit from the emphasis of movement in a shot - even when the movement is very small, slow and/or subtle.
Slow Down - Your shutter speed, that is. As we said at the outset, being able to shoot with a slower shutter speed is an advantage of having less light. Movement is represented by blur. When the shutter is open is long enough your camera lets you ’see’ the movement of your subject as ghosting or blur.
At 1/1000 of a second the subject has to be moving very fast before you will see any motion blur; while if you select a long shutter speed (say, 5 seconds) you don’t need your subject to move very much at all before you start to see blur.
It isn’t the actual speed of the subject that matters, but the relative movement across the image plane. So the jet aircraft a 600 mph can be stopped at 1/50 sec. when it is a mile away and moving towards you, while the woman walking 3 metres away will be a blur as she crosses parallel to the plane of your focal plane at 1/200.
Obviously, then, the shutter speed that you need to show motion as a blur or a trail will vary a lot depending upon the speed of your subject, how much blur you want, and how well lit the subject is. The key is to experiment (something that a digital camera is ideal for).
There are two ways to get a feeling of movement in your images - have your subject move or have your camera move (or both).
A Stable Camera - Any movement in your camera for this kind of work most be controlled. If your camera isn’t perfectly still, it won’t be just the subject that shows motion: the whole frame will look fuzzy or like it’s moving as a result of using a longer shutter speed.
You need support: a tripod is the best option, but if you don’t have access to one, have your camera sitting on a stable object. A cable or other remote shutter release, or the self timer, will improve your chances of successful slow shutter photography, and in some cases, locking the mirror of your SLR up before taking the shot helps...the “slap” of the mirror whipping out of the way can be enough to spoil the picture.
Shutter Priority Mode - Changing the 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. You could use manual mode, but this is exactly what Shutter Priority Mode was designed for. Shutter Priority allows you to concentrate on getting the ideal shutter speed knowing that the camera will sort out the correct aperture for a well exposed photo.
Long Shutter Speeds in Bright Light - Obviously, a smaller aperture helps; but in bright light, even at the smallest aperture, you may not be able to get a good exposure at the shutter speeds you want. You have several options:
A Lower ISO -ISO refers to the sensitivity of your medium to light. The higher the ISO number the less light is required to make a good exposure. ISO numbers are linear: double the ISO, halve the exposure. Therefore, if you choose a low number and you’ll be able to use longer shutter speeds. Films with speeds in the 25 ISO range are excellent for this approach. Digital photographers are less well served, with most unable to set an ISO below 200. Canon SLRs and the most recent top-line Nikons go down to 100 ISO, but that’s about it.
Neutral Density and Polarising Filters - Imagine you’re shooting a waterfall in a brightly lit landscape. You want to use a shutter speed of 2 seconds. You have cut your ISO to the minimum, but you are still going to end up with a badly over exposed image. A ND filter is your best friend. These filters cut down the amount of light passing through your lens without affecting the colour. This allows you to use a slower shutter speed. Think of them as sunglasses for your camera - I’ve heard of people actually using sunglasses when they didn’t have an ND filter handy, but I’ve no idea what sort of image those small, curved lenses produced!
A polarising filter will have a similar impact but polarisers do more than cut out some light. They reduce reflection and can change the colour of a sky which may or may not be the look you’re after.
Slow Synch Flash - So far we have been using slow shutter speeds in daylight. In darker situations (not necessarily night-time) we can use the very fast flash of a strobe (i.e. your electronic flash gun) combined with a longer shutter speeds. Elements in the shot lit by the flash (at 1/1000 and faster) will be “frozen” while others will be blurred by their motion.
Some cameras allow you to set exposure length and flash strength but on many compact cameras slow synch is hidden behind the less intimidating name ‘night portrait mode’ or similar. It usually comes with the advice to make sure your subject doesn’t move after the flash fires, or they will have a ghost image, too - that is really only true if the ambient light is g=fairly bright, and anyway, you might want the effect! Experiment!!
Rear and Front Curtain Sync - More advanced cameras offering slow sync flash might also let you choose between ‘rear curtain sync’ and ‘front curtain sync’. These two modes determine whether the flash fires at the beginning of the exposure or at the end, and only apply to shutters which work like a blind travelling across the film/sensor plane.
At ordinary shutter speeds, these “focal plane shutters” expose the sensor in a strip, bit by bit. For flash, a first blind opens, the flash fires, then a second blind closes to shield the film/sensor from any more light. Standard flash is synchronised so that it fires when the blinds are fully open. Since the curtain moves across the sensor left to right (or up to down), one side of the image receives a little more exposure than the other.
Rear Curtain Sync tells your camera to fire the flash at the end of the exposure. ie when you press the shutter your lens opens up and starts collecting light and just before it closes the flash will fire to light up and freeze your main subject.
With Front Curtain Sync the opposite happens: your camera to fires the flash immediately and the shutter remain open afterwards capturing ambient light.
Front Curtain Synch is the standard, but shoot a moving subject with this and you will see a motion trail ahead of the subject as though they were going backwards!
Faking Motion - Image editors have several tool that allow you to simulate motion. Some are filters that affect the entire image, others can be applied selectively to parts of the image. I only mention them here for interest sake, and I may address them in detail in a separate post.
for now, there are techniques and ideas enough to go on with!
