Shooting Starbursts and Sun Flares
Sometimes you need just a little something extra to get the perfect shot. Rendering the sun with a starburst effect isn't hard once you've learned how.
But before I get started here today, I need to dispense with my obligatory warning. You should avoid looking directly at the sun. It's bright. No doubt you've noticed. No doubt you'll notice all the more if you overdo it as doing so can damage your eyesight. To the naked eye, it can leave you with an after image that lingers for some time and follows your gaze as you turn your head. Viewed through a telephoto lens, it can burn your retina. If you go in for the vast landscape shot instead, you're somewhat better off since a wide angle lens decreases the intensity to a degree rather than magnifying it. Were the sun truly a point source of light, the lens wouldn't matter, but the size of the sun's disc does change with the choice of focal length, and thus does its capacity to damage your eyes. But still, be careful out there folks.
Now for the basics of what causes a starburst. The sun itself is blazing down without regard to you and your camera lens. It's not the sun that causes a starburst, it's your lens. More specifically, it's the aperture in your lens and an optical effect known as diffraction. As light waves pass through a lens, they get directed and focused. Passing near the blades of the aperture diaphragm, they get bent slightly off course from where they should be focused. This is diffraction. The effect is more noticeable at small apertures since those aperture blade edges constitute a greater proportion of the total area through which incoming light can travel at smaller apertures. That is to say, the ratio of the circumference to area goes up when the diameter of the hole decreases. And since that aperture opening changes size by means of overlapping blades, each blade edge causes its own diffraction, channeling the sun's brightness to form a single ray of the resulting starburst. Effectively, the light that should spread out uniformly from the sun's disc gets bent into rays along the lines of each overlap of the aperture blades. And thus a starburst is formed. If your lens aperture had no blades, such a distinctive starburst pattern wouldn't form.
At extremely small apertures, diffraction can become a cause of decreased apparent resolution and sharpness since it affects everything, not just the sun. Just how small is "extremely small" depends in large measure on the size of your image sensor, but on a Nikon DX (APS C) sized sensor its effects can become measurable by f/22 which most modern lenses are capable of shooting at. Larger FX sized (so called "full frame") sensors probably won't show much softening till you get to f/32 which some macro lenses can reach, but not most general purpose optics. Regardless, it isn't necessary to immediately go all the way to f/22 when trying to shoot starburst patterns. I often find f/16 completely satisfactory for the task at hand.
Exposure for starburst can be somewhat tricky at first. Since the sun is clearly so much brighter than anything else that will be in the frame, the tendency is to either over or underexpose starburst images, depending on where you meter. If you meter directly on or too near the sun, it will come out medium toned and everything else will be rendered too dark. Meter on the foreground landscape and the sun will be burned out white. Given that the eye is accustomed to seeing the sun as blazingly bright (hence my caveat at the outset about avoiding damage to your eyesight), you are better off opting for the latter exposure strategy. Don't worry about the sun and expose for the rest of the scene.
There is, though, an exception to this exposure rule. And it's a great way to have your cake and eat it too (or should I say "have your foreground and a well exposed sun too"). High Dynamic Range (HDR) photography involves digitally combining multiple in-camera exposures to create a composite image result that appears to exceed the exposure latitude of any one exposure. So long as your subject isn't likely to move much too quickly, you can shoot exposures ranging from a well exposed foreground and subject, to a well exposed sun, and everything in between, and then combine them later in the digital darkroom. You'll need to solidly mount your camera on a tripod to achieve good results. It won't matter much if your subject stays steady if your camera is moving all over. Then determine your starting point exposure for the foreground. Shoot progressive images starting from that exposure and continuing on until the result is completely black. Since a small aperture is essential to create the starburst effect, you're generally better off varying your successive exposures by means of shutter speed than by changing the aperture.
Don't stop think that you can stop early either. If you peak at a frame on the LCD camera back display and see a small starburst suspended in an otherwise black frame, you aren't done yet. If you do stop there, you're liable to find your resulting HDR image suffering from unnatural edges surrounding that final darkest frame starburst. You need usable exposures that extend all the way to complete darkness to ensure your HDR software (Lightroom, Photoshop, SNS-HDR Pro and others) have enough source material to work their magic.
In addition to shooting directly at sunset with the sun in the frame, you may find it advantageous to also shoot sufficient exposures of your chosen scene to create an HDR before the sun drops into the frame (assuming sunset, or of course after it leaves the scene at sunrise). Then, when you later combine what you end up with, you can achieve colorful clouds, golden hued subject matter, and your desired starburst. Glare from the sun can decrease contrast once it does enter the frame, so having some images to work with without it, but that will appear natural with it, can be a huge plus. I will sometimes combine a more or less single shot foreground shot an hour before sunset with an HDR sky and background shot at sunset. As you might be realizing at this point, you need to commit to a scene and stick with it for a reasonable timeframe in order to end up with the best results once you combine things. All this extra work isn't really cheating either (in my opinion) since the reason for doing it at all is to overcome the limitations of real world photography with real world cameras and lenses. I never attempt to create something that didn't exist. I'm only interested in creating images that could have been seen, if all those limitations could be removed.
Before shooting, make sure your lens glass is as clean as you can get it too. Glare can affect not only the scene before you, but the ability of your lens to render it clearly. A stray fingerprint or smudge can ruin an image with the sun in the frame, or at least greatly complicate your Photoshop touch-up efforts later.
You'll also get better results on days without discernable haze. Fog or haze in the sky can diffuse the sun's light sufficiently before it even gets to your stopped down lens to make the creation of a starburst far less likely.
You can also create starburst effects from light sources other than the sun, although I tend to find few compelling alternatives that don't end up looking like they were shot with a cheap starburst glass lens filter. Far too many beginning photographers fall for the marketing material from Tiffen and other filter makers, and end up believing that these silly filters are the way to shoot starburst images. Don't fall for it, and don't shoot images that look like you did.