Sunstars

Gary Hart Photography: Autumn Morning, Half Dome and Sunstar from Sentinel Bridge, Yosemite

Autumn Morning, Half Dome and Sunstar from Sentinel Bridge, Yosemite
Sony a7RIV
Sony 24-105 G
1/15 seconds
F/20
ISO 100

As striking as they might be, some people find sunstars (AKA, diffraction spikes, sunbursts, or starbursts) gimmicky and cliché. When I (and pretty much any other landscape photographer) arrive at a location, of course I hope for some combination of dramatic clouds, vivid color, and soft light. But when the sun dominates the scene, it turns out that including a sunstar is usually the best way to get the most out of the moment.

Adding a sunstar to a photograph does have its challenges: Including any part of the sun in your frame introduces lens flare, not to mention extreme (often unmanageable) contrast. And poorly executed, a sunstar creates an unappealing eye magnet that overpowers the rest of the scene. And while a sunstar doesn’t capture the literal experience of watching the sun’s arrival or departure, it’s almost always better than a washed-out blue sky.

For a long time I considered sunstars merely a lemonade-from-lemons solution—the best way to play a poor hand. But over time I’ve come to appreciate a sunstar’s ability to represent the brilliance of gazing directly into the sun—minus the corneal damage. Like blurring whitewater and waves or freezing airborne droplets to convey motion, a sunstar can serve as a proxy for a natural phenomenon that’s impossible to duplicate in a still photo.

The truth is, the sun is a powerful conveyer of emotion. We all have fond memories of watching the day’s first or last rays as the sun peeks above, or slips below, the horizon. And who doesn’t feel relief when moving from sunlight to shade on a blistering summer afternoon, or from shade to sunlight on a chilly winter day? A sunstar can freeze these natural transitions in a still image, subconsciously stirring their associated emotions.

So what’s going on?

A sunstar forms when brilliant, direct sunlight (or any other bright light) diffracts (spreads) as it passes through the overlapping blades of a lens iris (its aperture). These are the blades that open to admit more light (small f-number), and close to limit light (large f-number).

It’s true that the more circular the aperture opening, the more pleasing a lens’s bokeh. But it’s impossible to get past the fact that you can’t make a perfect circle by connecting a series of straight lines (which is what each aperture blade is). Adding blades helps keep the aperture iris more circular, but as the lens stops down (smaller aperture) to allow less light to pass, the angle between adjacent blades steepens and the more the emulated circular shape (remember, it’s never a true circle) becomes a more obvious polygon—connected straight edges, one for each blade, with each blade intersecting its adjacent blades at identical angles totaling 360 degrees.

As sunlight crosses the straight line made by each iris blade, diffraction spreads spikes of light in both directions perpendicular to the blade. If the lens has an odd number of iris blades, each spike will appear in your sunstar—2 spikes for each iris blade. Lenses with an even number of blades consist of pairs of exactly parallel blades opposite each other around the opening; the diffraction spikes of each matching pair overlap, so you’ll see just one spike for each blade. In other words, the amount of spikes in your sunstar is a function of the number of iris blades in your lens: with an even number of blades you’ll see one spike per blade; with an odd number of blades, it will be 2x the number of blades.

Light diffracts (spreads) as it passes through a small opening—the smaller the opening, the greater the diffraction. Since diffraction reduces resolution, we usually we try to choose apertures that minimize diffraction. But when a sunstar is the goal, a small aperture makes the sunstar more distinct.

Sunstar how-to

If you’re still with me, you’ll be happy to know that creating a sunstar is much more straightforward than understanding its optics. Here’s a quick recipe:

Start with a brilliant point of light: You can create a sunstar with any bright light source—the moon, stars, or even an artificial light such as a lighthouse, or car headlights—but I’m going to talk about the brightest, most ubiquitous, and easiest light source: the sun. Rather than using the entire sun, it’s usually best (but not always—you decide the look you prefer) to block most of the light with the horizon, a cloud, or some terrestrial feature, such as a rock or tree. And clouds and atmospheric haze can reduce the brilliance enough to significantly limit your sunstar. Sometimes I’m not even aware of clouds or haze until I see the sunstar spikes are faint, spread out, or non-existent.
Different lenses will yield different results: Experiment with your lenses to see which one gives the most pleasing sunstar effect. As a general rule, wide lenses are better, and the better the quality of the lens, the better its sunstar effect. Prime lenses tend to do a better job, but today’s best zooms create beautiful sunstars too, especially at their widest focal lengths. Remember, the number a sunstar spikes is determined by the number of diaphragm blades.
Remove filters: The more glass between the sun and your sensor, the more reflections and lens flare you’ll get, so remove your polarizer (which has no benefit anyway when you’re pointing at the sun) and UV filter. If you must use a graduated neutral density filter to hold down the dynamic range, go ahead.
The smaller your aperture, the better your sunstar: A wide-open aperture is a nearly perfect circle (not good for sunstars), but the angle between the diaphragm blades increases as the diaphragm closes down, improving the sunstar as the angles increase. For my sunstars, I generally stop down to f/16 or smaller (larger f-number)—usually f/18 or f/20.
Size matters: The larger the visible portion of the sun, the bigger the sunstar, but also the more lens flare and blown highlights. Conversely, if most of the sun is blocked, you’ll get a smaller sunstar, but it will also be more precise and delicate. There’s not absolute ideal size, it’s more of a balancing act to find the right mix for your taste and situation.
Composition: The extreme dynamic range of a sunstar image makes it essential to photograph the scene the way your camera sees it, not the way your eyes see it. I generally set up my composition before I meter, brightening the foreground enough to make it plainly visible in my mirrorless LCD (ideally I do this before the sunstar appears). If you’re new to sunstar photography, or don’t have a camera with lots of dynamic range, a silhouette or high key image are good options. Start with a foreground shape, or shapes, that standout against the sky—for silhouettes, meter on the sky and underexpose; for high key, meter on your foreground subject and overexpose slightly (to turn the sky white or nearly white—see poppy example in the gallery below).
Manage the highlights: With the sun actually in your frame, you’re invariably dealing with a sky that’s much brighter than your foreground—overexposed highlights and underexposed shadows are virtually unavoidable. To maximize the usable data you capture, start with a raw—a jpeg file just doesn’t have enough dynamic range to handle the extreme highlights and shadows of a sunstar image. Nevertheless, it’s likely the image will look like crap on your LCD—even in a properly exposed sunstar image, the highlights will probably look too bright and the shadows will look too dark. On the other hand, if the sky looks great, the shadows are probably hopelessly dark (unrecoverable); if the highlights look great, the sky is probably hopelessly bright. When I’m exposing for a sunstar, I watch the histogram (a benefit of mirrorless photography is the pre-capture histogram in my viewfinder) and try to find a balance between the extreme highlights near the sun, and the dark shadows of the surrounding scene. In most of my photography don’t bracket for exposure, but sunstars are one significant exception. Since the dynamic range is so extreme that the histogram shows both shadows and highlights completely clipped (blown), I try to start with an exposure where their both more-or-less equally clipped, then bracket over at least a 6-stop range (3 stops up and down from my midway starting point) in 2/3-stop increments, changing exposures as rapidly as possible to give me a good number of different exposures to choose between.
Processing: I promise that you’ll need to do some processing to get the most out of the highlights and shadows, but take a look at my gallery below—each image was captured with one click (no HDR or any other multi-image blending), and most (all?) were captured without a GND filter. My usual processing approach is to start with one of the frames near the middle of the exposure range that I used, pull the Highlights slider all the way to the left (-100) and pull the Shadows slider all the way to the right (+100). Then I pull the exposure slider to the right until satisfactory detail appears in the shadows. If this brightens my highlights too much, I discard these changes and move to a darker image. Following this approach, I can usually find at least one frame with usable shadow/highlight balance.
Practice: You can practice sunstars any time the sun’s out. Just go outside with your camera, dial in a small aperture, and hide the sun behind whatever object is convenient (a tree, your house, etc.).