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Composing the Universe: planning your composition can raise your imaging to a whole new level.

The art of deep-sky astrophotography differs from most other types of picture-making. Astro-imagers learn the fundamental techniques of combining many long exposures to suppress noise while simultaneously increasing the signal to reveal ever-fainter objects in their images. Tools such as calibration frames, pixel rejection methods, and tri-color technique are mostly unheard of in other types of photography.

But many fundamentals of photography remain the same whether your subject is a distant galaxy or a picturesque landscape. Color balance, contrast, and composition come into play in every great image, no matter the subject. As imagers strive to raise their work beyond the point of simple picture-taking, composition and visual aesthetics become important considerations in the journey to create a truly memorable photograph. Here are some ways to consider your next target--before opening the shutter--that can add drama and power to your compositions and set them apart from the crowd.

Zeroing in on the Focal Point

In order to push our images to that higher level, it's important to ask ourselves the question that artists throughout history have asked themselves: What do we want the viewer to concentrate on? This is the focal point of the picture, the main subject that inevitably draws the eye and commands the most attention.

When planning a composition, I often mentally divide the picture into three components--the focal point, supportive structures, and background. These elements may be obvious, such as a galaxy (the subject) surrounded by a few bright stars (supportive structures), and the background of dimmer stars in a sea of black. But they might also include less obvious divisions, particularly when shooting sprawling nebulae. We might designate the subject by increased brightness and contrast, for example, or by highly defined structures or color emphasis.

Subtle structures in the image have importance, too, but they play a supportive role in directing the viewer's journey to the natural focal point by way of visual or directional cues. By doing so the viewing experience becomes an orderly passage in which the elements within the image function like coordinates in a GPS, guiding the viewer in a logical and satisfying journey through the image.

Happily, most astronomical subjects have a natural focal point. Examples include the bright nuclei of galaxies or the brilliant young stars within bright nebulae such as the Trapezium within M42, the Orion Nebula. But interesting targets exist that lack a natural focal point, such as a nebulous field that stretches beyond your camera's field of view. In this situation it becomes your task to establish the focal point through creative framing of the scene, using the supporting structures to create the illusion of a natural focal point.

The focal point doesn't have to occupy the center of an image. Many fine examples exist of asymmetric focal points in successful astro-images. One caveat: if the focal point is off center, then a supporting structure needs to occupy the area opposite the focal point. This could be a smaller, more distant galaxy juxtaposed against the brighter and larger galaxy subject, or a fainter open cluster of stars. The key is to allow the main focal point dominance in the image through positioning, brightness, or selective sharpening.

Creating Visual Flow

When viewers examine an image for the first time, they need visual cues to lead them through it, as alluded to above. This process is known as "flow"--the subtle directing of a viewer's eye through an image.

Offering engaging flow is essential because as astrophotographers we work with static subjects. We're forced to utilize the existing elements of our chosen scene while working with the variables we do have control over, including light, color, scale, depth, and symmetry. We can use all these elements to enhance flow. Framing is also critical. Astronomical scenes often have supporting structures such as dust clouds, stars, or distant background galaxies, for example, that the photographer can frame in such a way as to create a sense of flow in an otherwise static image.

Striking a Balance

Proper balance is one of the most crucial compositional elements. As a rule, pleasing balance results from appropriate contrast between the focal point, supporting structures, and the background. A group of bright stars framed along one side of an image, for example, can serve as an important directional cue, leading the eye to the focal point and helping to establish a dramatic composition.

On the other hand, while colorful star fields can be striking, if stellar intensities are too strong they can detract from an image's focal point and supporting structures. Imagers sometimes use several tools to suppress the intensity of stars in an image, including the minimum filter and the spherize tool in Adobe Photoshop. These tools are best applied selectively and sparingly to only those stars that detract from the focal point.

Depth of Field

One challenge in astronomical image-processing is creating the perception of three dimensions in a two-dimensional image. Often the highest praise for a stunning astrophoto is that it conveys a sense of depth and perspective.

If the focal point of an image has greater detail, color intensity, or contrast compared with the supporting structures, the viewer is given the perception of depth. Some targets, particularly when shooting a tight close-up within a large nebula or dense star-field, may require additional processing to impose that coveted sense of depth.

Selective sharpening of key areas in an image full of bright and dark nebulae can often add a vivid sense of depth to an image. To enable the viewer's eye to zero in on the subject quickly, you can leave regions within your photo "softer" than the area you've designated as the focal point. A similar approach works well when imaging galaxy clusters or star clouds within the Milky Way.

Complementary Colors

Color composition can also be integral to the success of an astrophoto. When shot in natural color, astronomical objects tend to display a limited palette of blues, reds, yellows, and blacks. A glance at a color wheel will reveal that certain colors have greater appeal when they appear opposite their complementary color. The bluish reflection nebulae that often appear adjacent to reddish emission nebulosity within the plane of the Milky Way, for instance, can contribute to a pleasing composition. Knowing the hues of objects in advance can often help you to create stimulating color contrast.

Astrophotographers working with narrowband filters have more leeway to take advantage of complementary color schemes, because they can assign each narrowband image to a different color channel to achieve dramatically different results than imagers working in RGB color.

Format Decisions

One of the simplest but most important processing decisions is how to manage the aspect ratio of your image. Should you present the image in landscape or portrait mode, or as a square? This choice can have profound effects on the visual impact of an image.

You'll want to ask yourself: what is the dominant axis of the structures in the image? If objects tend to run along the horizontal axis, then a landscape format will likely be in harmony with those structures and offer a more appealing viewing experience. A composition with mostly vertical structures will benefit most from a portrait composition. And fields in which the long axis runs diagonally or targets a well-centered, round focal point will likely present best in either square or nearly square format. Whatever orientation you choose, try not to fight the natural dominant axis of the object.

When I complete an image, I often experiment liberally with cropping--shrinking a field of view around a small galaxy, say, or getting rid of distracting secondary structures--as well as rotating the image to find the most appealing presentation. In astronomical imaging, one cannot change his or her viewpoint to the object, but managing the scene by way of framing, cropping, and rotating can produce some spectacular results.

Rules, Rules, Rules

In traditional photography the well-known rule of thirds and its variations are helpful guidelines for composing a picture. The rule of thirds suggests that when planning a composition, the photographer should divide the image into a grid of nine equal parts by mentally placing two equally spaced horizontal and vertical lines over the field. The photographer should then position salient compositional elements at the four points of intersection.

This compositional strategy produces a visual storyline with energy, direction, and flow accentuated by a more intriguing off-centered focal point. Significant structures need not fall precisely on the points of intersection to take advantage of this rule. Astronomical objects that benefit most from the rule of thirds are C- or U-shaped nebulae, galaxy clusters, and complex star-forming regions with juxtaposed star clusters and nebulae.

Composing Panoramas

One of the most daunting tasks in astrophotography is producing effective wide-field panoramas. By their nature they are exclusively mosaics, so you have greater opportunities to plan the composition and position key objects and focal points in advance.

Because of the extreme aspect ratio of panoramas, they often require some deviation from the standard compositional rules. The rule of thirds or a single focal point --mainstays for non-panoramic images--do not always work with positioning vital objects and structures within an astronomical panorama. You might position key objects or main focal points of the vista within the center third of the image, for instance, with supporting structures and background elements filling the outer thirds.

In sum, composing astronomical scenes can be challenging due to the limitations of photographing static celestial objects from our fixed viewpoint. But taking time to carefully plan the composition before beginning the first exposure can make the difference between an adequate image and a timeless treasure.

Learn more imaging techniques in author Robert Gendler's latest book Lessons from the Masters: Current Concepts in Astronomical Image Processing, from which this article was adapted.
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Title Annotation:Imaging Aesthetics; photography tips
Author:Gendler, Robert
Publication:Sky & Telescope
Geographic Code:1USA
Date:Jan 1, 2015
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