There are a host of complexities associated with photographing bright lights, not least of which is how to make areas of a photo that are likely to be over-exposed appear visually pleasing. In landscape photography, the sun often sits at the heart of this challenge and one way to deal with the blazing orb is to make use of a phenomenon known as the starburst effect.
The starburst effect, otherwise branded the Star Effect, Sun Star, or Sun Flare, is an optical anomaly produced by the influence of the aperture blades on the light entering a lens. Among the many curious properties of light, its habit of changing direction when confronted by an obstacle – such as an aperture diaphragm – continues to delight and perplex physicists to this day. It is important to understand that light waves only travel in straight lines; however, when they encounter an obstruction, their course suddenly changes. A light wave travelling towards an obstacle in a given direction departs from that obstacle – still traveling in a straight line – but now in a new direction.
The apparent bending of light around a barrier is known as ‘diffraction’, while the pattern made by the diffracted light is known as an ‘interference pattern’. A starburst is little more than the physical manifestation of one of these interference patterns and there are two key characteristics of an aperture diaphragm that dictate its appearance – the size of the opening and the number of blades.
Despite all the complicated physics that explain why a starburst exists, for photographers wanting to create the effect, the method could not be more straightforward. All it requires is a high contrast scene – a sunset or streetlights at night – and the choice to use a small aperture setting. The degree to which light is diffracted is directly related to the size of the obstacle it encounters. Force a lot of light through a small hole and you get a lot of diffraction, making the resulting interference pattern easier to see.
By comparison, the number of blades that make up an aperture diaphragm only truly influences the aesthetic of the starburst. The greater the number of blades the higher the number of rays – although this widely held truth can be a little misleading. An even number of blades creates rays that overlap and, consequently, an odd number of blades always produces more visible rays than the next biggest even number. Typically, more expensive lenses use more blades in their diaphragms in an attempt to approximate the ideal – a circular aperture. Although purely a subjective matter, a high ray count, as it were, is ordinarily viewed as more pleasing than images with fewer rays.
A third significant but less spoken of requirement for a good starburst is contrast. Diffraction is a phenomenon that takes place at all aperture settings and under all lighting conditions, although the effect is, more often than not, invisible. Observing an interference pattern essentially demands using a smaller aperture than one ordinarily would for the given lighting conditions and, even then, the effect is very subtle. For diffraction to truly become apparent, a scene must possess a bright light source behind a substantially less bright foreground. The greater the contrast between the source and the foreground luminance, the longer the starburst’s rays will appear.
As with everything in life, there is no such thing as a free lunch, and using a small aperture to create a starburst is not without its drawbacks. Diffraction is not something that any lens manufacturer hungers after but is rather an unavoidable physical limitation that they would sooner be without. Whether visible or not, the presence of any diffraction at all in a lens reduces the resulting image sharpness – the greater the diffraction, the softer the final photograph. Most lenses have a distinct point at which diffraction becomes the biggest contributor to any loss of image sharpness – normally at around f/11. When you consider that to create a tight and well-defined starburst requires shooting with an aperture setting more in the region of f/22, the magnitude of the sharpness problem becomes apparent.
For those of you who are in the habit of pixel-peeping, the loss of sharpness required to shoot a starburst might be too much. There can be no arguing away the negative impacts of the technique. With that said, the starburst effect can be a spectacular addition to a photograph when used appropriately. It possesses the ability to almost single-handedly evoke a sense of awe in the audience, a quality that far outranks technical perfection in terms of importance. Crucially, the ability to experiment with and use the starburst effect is something that every photographer enjoys. There is no need for additional gear or elaborate post-processing. The next time you see the sun dropping below the horizon, simply narrow your aperture and point your camera in its direction. You may be amazed at the results you achieve.