An Introduction to Long Exposure Photography
Long exposure photography is a creative photography term and one that uses techniques that involve keeping the lens open for a long period of time and thereby capture a lot of light in the process. While doing so the photographer, usually capture a lot of motion blur as well. Thus, long exposure photography is not only about capturing a lot of light, but also motion which tend to produce creative blurry effects. Let’s have a deeper understanding of these terms and how we can create long exposure photos of our own with simple tools.
But before we go any further into long exposure photography techniques we need to have an understanding of the term ‘Exposure’. Exposure denotes the total amount of light that is captured by the sensor / film. It is a product of the length of time for which the lens remain open and the aperture of the lens. Aperture, as you are aware off, is the opening of the lens.it is controlled by the aperture diaphragm blades. When you press down the shutter release button the aperture diaphragm blades open up creating a hole through which light passes. The length of time for which the lens remain open to expose the sensor to light is controlled by the shutter mechanism of the camera. It is known as shutter speed.
You would probably be thinking at his point whether I missed referring ISO in this. ISO does not dictate the amount of light that reaches the sensor. It is concerned with what the sensor does after that light is captured. ISO denotes the sensitivity of the sensor to light. To explain ISO in film parlance we can state that ISO is equivalent to ASA. Just as we had different ‘speed’ films back in the days of film camera, we have changeable ISO feature on our camera. Back in the film days it was impossible to change the sensitivity of the film we shoot unless we pull out the film inside our camera and use a different film with a different speed.
What Happens When You Keep The Lens Open For A Long Time?
When you do that, i.e., keep the lens open for a long time, you are basically allowing the lens to capture a lot of light over a period of time. To achieve this set your camera on shutter priority mode (Tv or S depending on the camera you have) and select the time frame for your exposure. It helps if you have a camera that has a low noise signature such as the Sony A7R II.
Why Would You Do That?
There are a number of reasons really, for which you would want to keep the lens open for a long period of time. One of them is definitely when you are shooting in a situation where there’s not enough light to go around. You would try to maximize and get a better, more well exposed photo, given the conditions, by keeping the lens open for a longer than normal time frame. Another reason may be to deliberately get a creative blur effect going. Let’s look at a few examples and how the image undergoes a complete transformation when you actually use a long exposure.
Landscapes Using Long Exposure Photography Techniques
I love shooting landscapes. No denying that. I love it even more when I can use a long exposure to capture movement. Movement in the form of the clouds rolling in, water gushing by and people or cars moving in and out of the frame. There are a million different creative things that you can try out using long exposure techniques. It adds a dramatic effect to the whole image.
Use Of Neutral Density Filters In Long Exposure Photography
With landscapes, especially, those shot at daytime, you would need a neutral density filter. A neutral density filter ensures that the image is not ‘washed out’. This can easily happen when shooting at daytime when longer exposures are impossible without the help of additional tools like ND Filters.
What Are ND Filters?
ND filters are required almost always when shooting in bright conditions. Yes! It is possible to use the long exposure technique even when shooting in day light conditions. Thanks to these wonderful pieces of glass. ND filters are like shades for your camera. They work very similar to how your normal sunglasses would work. Except for the polarizing effect. There are other specialized filters for that. I will come to those in a moment.
A normal sunglass cuts down on the brightness of the scene thereby allowing our eyes to have a normal view of it, even though conditions are extremely bright. The same way a ND filter will cut down on the amount of light entering the lens, allowing the lens to ‘see’ longer without over-exposing the scene.
These filters are available in different light stopping powers. You would get ND filters of the power ND2, ND4, ND8 and so on. Each higher number basically halves the amount of light than the previous smaller one. That means a ND2 would stop one stop of light, ND4 will stop two stops of light (quarter of the original light reaching the sensor) and so on.
With each increasing light stopping you would be able to use a consequent slower shutter speed. Choose not one but several of these filters with different light stopping power. This is so that you have different options in your hand when at the location shooting long exposure photography. Let’s take an example.
Let’s say that you are set up to photograph a waterfall. The camera meters the scene at f/11 ISO 200 and shutter speed 1/100 of a second. At that exposure you will get a fairly good image of the scene. But that wouldn’t give you the exposure that you are after, a dreamy milky white effect to the water. For that you need to slow down the shutter and capture a lot of motion blur.
To do that set-up your camera on a tripod. Meter for the scene. Then add the ND filter. The filter you would select would depend on the shutter speed you would want for the effect you are after. A ND2 will increase the exposure time to 1/50. ND 4 to 1/25 and so on. For really dramatic effects select something like the ten-stop Lee big-stopper. After you add the filter set your requisite exposure. Basically it is mental math from here on, based on the initial metered exposure and the filter you have selected.
Photographing Brooks, Waterfalls Etc.
These are slightly tricky subjects because of two reasons. The water is a reflective surface and that means it is likely going to be at the bright right corner of the histogram when you meter it. Secondly, you will need to cut down on the glare. Thus you need both a ND filter and a circular polarizer.
Circular polarizers are another type of filters. These are used to cut down glare, reflections and haze especially when shooting landscapes, shiny surfaces such as water, automobiles and products set against shiny surfaces. In the example above I described how to use a circular polarizer together with a ND filter. These filters are a landscape photographers quintessential tools of trade. There are hardly a landscape photographer who would leave home without a ND filter set, circular polarizer and tripod.
The circular polarizer is frequently used in tandem with the ND filter. There are filter holders available that allow you to stack these two different filters. This is probably a better solution than manually trying to correct the glare later on during post-processing.
Long exposure photography do require a bit of post-production. This would include but are not limited to brightness adjustment, highlight adjustment, bringing up the shadows and contrast. In most cases these involve just a few mouse clicks and drags.