How often are you faced with a situation where you want to make a portrait image and the light is extremely low? Normally, when we attempt shooting portraits handheld in bright light, we set the shutter speed to something very high. The idea is to freeze any movement that the model or the hands make while the exposure is being made. It invariably results in a sharp image. However, in low light situations, the lack of light is an impediment to using fast shutter speeds. In order to shoot hand-held portraits in such low light situations, we have to adopt a few techniques.
Related Post: Best Portrait Photography Lenses
Here are a few techniques that you can use:
1. Use wide aperture: Advantages
To achieve a fast shutter speed we need to set the aperture to something as wide as f/2.8 or if possible even wider. It helps in two ways. First, it allows us to use a fast shutter speed (shutter speed and aperture have an inverse relationship, increasing one will warrant deceasing the other).
A wide aperture signifies that the lens is opened to its maximum to let in more light. With a lot of light, if the lens is open even only for a small amount of time, enough light is captured for a proper exposure.
This is where a dedicated fast prime portrait lens scores over a kit lens.The other major advantage is that much of the background can be rendered blurred. Blurring the background helps us to isolate the subject from the background. This is not a mandatory requirement but it looks quite well in the final image. The quality of the background blur is popularly referred to as Bokeh. The word Bokeh has been taken from the Japanese dictionary.
2. Using a kit lens: Pros & Cons
There is one problem in all these. Not everyone has a fast prime lens. There are cheaper alternatives but then you only get what you pay for in the final results. Beginners mostly have a kit lens to fall back on. The biggest drawback to using kit lenses is that you cannot open it wide enough. You are pretty much stuck at f/3.5 and that too at the wide end. At the tele end it can open up to only about f/5.6 to f/6.3. These are unsuitable for low light portrait photography.
Related Post: Zoom Lenses vs. Prime Lens
Interestingly, the first and the most obvious solution to this problem is to slow down the shutter speed. Slowing down the shutter speed results in more light to be captured over a longer period of time. More light means you get a proper exposure for the subject, despite the lack of ambient light. But didn’t we just finished reading a paragraph on the evils of slow shutter speed? Yes we did and this is where image stabilization comes into the picture.
3. Use Image Stabilization
Your trusty image stabilization is like a life-line when shooting in low light situations. If your lens comes with image stabilization, by all means use it. What image stabilization does is it uses several elements, gyros and other software to keep an image in focus if the camera moves along the vertical axis.
Modern lenses routinely can stabilize an image and give you the flexibility to use a shutter speed of two stops or slower. In other words you can use a shutter speed that is two stops slower than usual when image stabilization is turned on.
4. Using higher ISO number
Notwithstanding what we learnt in the above paragraph about slow shutter speeds and image stabilization, what else can we do to tackle the problem of low ambient light; especially when we are working with a slow lens and thereby cannot set a wide aperture? The answer is we need to use a combination of slow shutter speed and higher ISO number.
Higher ISO has always been a taboo for photographers, not just digital but also film shooters. Today, however, with the kind of advancements that has been achieved in digital image sensor technology, image processing engines and post-processing software, using higher ISO is no longer a taboo. Setting a higher ISO actually, allows you to get a sharp portraits images without having to slow down the shutter speed and thereby inducing image blur.
What ISO to use? It all depends on the amount of light there is in the scene and the kind of image that you have envisioned. To start off, I sometimes crank the ISO all the way to 1600. It gives me a good breathing ground if I am using a slow lens. Depending on the exposure that I get I then dial it down. It’s all about balancing the depth of field, a shutter speed so that I can hand hold and then use the right ISO to balance everything.
Another way to achieve that balance is to consider what shutter speed you need for your shot. As you are aware shutter speed controls how much of the ambient light is captured. Let’s say that ambient light is really low, just street lights at a corner. You may have to use a very slow shutter speed, something like 4” to be able to capture enough light for the shot. This is impossible to be achieved handheld. Thus you need to crank the ISO higher to bring down the shutter speed to something manageable like 1/30 of a second. There are, however, some other parameters to consider as well.
5. An alternate method would be to use a tripod
A tripod eliminates any chances of the camera moving in your hands. But mind you, this is not an insurance against your subject moving. Just like image stabilization a tripod is for stabilizing the camera/lens and not the subject. If your subject is moving, use continuous auto-focus with a dynamic area AF mode.
Related Post: Best DSLR Tripods for Photography Beginners
6. Shutter speed – focal length relationship
In the previous paragraph, we learned how cranking ISO high allows you to speed up the shutter speed. This obviously comes from the inverse relationship between the exposure triangle elements. But what should be a manageable shutter speed in any situation? E.g., can we hand-hold a 1” exposure? No.
Our hands cannot hand-hold an exposure that is less than 1/30 of a second.
This is a general truth though individually some people may have steadier hands. The trick is never to use a shutter speed that is slower than the inverse of the focal length. Meaning, if you are using a 50mm lens, try not to use a shutter speed less than 1/50 of a second. Image stabilization, however, changes that equation. If you don’t have image stabilization always carry a tripod or at least a monopod with you.
7. Use the built-in flash
Finally, we come to the flash bit. Flash is a very powerful tool. In low situations, a flash not will give you a proper exposure but also helps you to freeze the movement of the subject and produce a sharp image. But simply firing the flash will not be enough. You will also need to sync the flash so that it fires towards the end of the exposure. In other words, you will have to use rear-curtain sync method.
Hope these above tips was an informative read and the tips help you to shoot sharp portraits in low light conditions.