Chapter 1: Introduction to Wide-Field Astrophotography Introduction to Wide-Field Astrophotography 1.1

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    Chapter 1: Introduction to Wide-Field Astrophotography

    1.1 Beginnings The word photography means “writing with light.” When we photograph something, we use various physical properties of optics, electronics, and chemical reactions to capture the object’s image and record it on a medium, whether that medium is a transparent plastic carrier (the negative), paper (a print), or a magnetic surface (digital imagery). When we apply these pro- cesses to celestial objects, we call it astrophotography.

    Eventually almost everyone who owns a telescope is struck with the desire to take celestial photographs. The beauty of the celestial sphere is too much to resist, and we succumb to the temptation of capturing the grandeur and spirit of what we see in the sky. If a person is already a shutterbug, his camera bag will likely have the needed gadgetry to begin photographic explorations of the cosmos.

    Photographing celestial objects through a telescope is one of the most demanding types of photography. Fortunately there is a way for novices to achieve success quickly and to capture on film the celestial delights that lure their gaze upward: in wide-field astrophotography with ordinary cameras, often known as “piggyback” astrophotography, one can start modestly and build the skills needed for more ambitious projects, yet achieve satisfying results. Basic piggyback photography does not require a lot of fancy equip- ment: beginners can start with any camera capable of time exposures and any equatorially mounted clock-driven telescope or tracking platform. If you do not already have a telescope, later in this chapter we will see how this can be accomplished with a simple homemade, hand-operated star tracking device.

    Astrophotography is full of surprises. With your camera, you may dis- cover a supernova millions of light years away, like Jack Newton in Victoria, British Columbia. Or, like Ed Szczepanski from Houston, Texas, you might find a new comet. Moreover, there is something special about starlight that has traveled longer than recorded civilization, or has been streaming toward

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    us since before humanity was on this planet: it carries a sense of immortality. If it went through such lengths to enter your camera, it deserves to be pre- served and admired.

    Some authorities have suggested that special skills are required to pho- tograph the night sky successfully; they warn that celestial photography is difficult and filled with such unusual jargon as “reciprocity law failure” and “hypersensitizing.” Yes, new skills are required. But celestial photography is not especially difficult, it is just different from terrestrial photography. Indeed, the most important attribute for those entering the field of sky pho- tography is the patience to learn a new skill.

    Beginners in the art of celestial photography should start simple and work their way up. Even if money is no object, a beginner should not be mes- merized by the hype in magazine ads for the latest telescopic wizardry. As with any endeavor, diving in without first mastering the basics will quickly lead to frustration.

    Astrophotography has two objectives: first, we want to record and share

    Figure 1-1: Is this a plate from Barnard’s classic Atlas of Selected Regions of the Milky Way? No, this beautiful image of the Sagittarius Star Cloud and the “Great Galactic Dark Horse” was taken with an inexpensive 50-mm f/1.7 lens on a Minolta SRT102 camera and hypered Kodak Technical Pan. This image demonstrates the versatility of the common cam- eras available to the amateur astronomer. Photo by Alan Sifford.

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    the beauty of the celestial vistas that we love; and second, we want to enjoy the technical challenge of mastering a new skill.

    This book assumes that the budding astrophotographer already has some experience with normal pictorial photography. Learning astrophotog- raphy will be much easier if the novice is already familiar with 35-mm cam- eras, interchangeable lenses, film speeds, and the techniques of film processing.

    1.2 The Bare Basics Wide-field skyshooting is astrophotography in its purest and original form, for it derives from the pioneering Milky Way photography in the late 1800s and early 1900s by Max Wolf and Edward Emerson Barnard. Their equipment was the state of the art for their time, but today’s amateur astro- photographer can capture on film the same fascinating celestial targets that Wolf and Barnard did with today’s inexpensive and readily available equipment.

    Indeed, beginners can start their astrophoto adventures with little addi- tional equipment beyond that used for regular photography, and interesting sky pictures can be accumulated without having to shovel vast amounts of cash into a new hobby. Because of the fast new color slide films, a darkroom is no longer necessary for quality astrophotography. Even electronic imaging does not have to be expensive for the beginner: if you have your pic- tures of celestial objects digitized onto a Kodak Photo CD, you can view and study them on your home computer.

    The temptation for the beginner to do deep-sky photography—of gal- axies, for example—through a telescope should also be avoided. Nothing will kill a novice’s enthusiasm faster than running into a wall of technical unknowns. A ladder of experience must be climbed first through wide-field astrophotography. Fortunately, this ladder is short and good results can be achieved quickly. The concepts and techniques learned in wide-field work are critical to success in later, more complex astrophoto work. Basic wide- field astrophotography is often regarded as the first step in a learning process that eventually leads to deep-sky photography. However, wide-field astro- photography can also be considered a field of specialization in itself.

    Many experienced amateurs actually take better sky photos than profes- sional astronomers. Indeed, professionals no longer have the time or incen- tive to do film-based astrophotography. The field is in the hands of amateurs, many of whom are obtaining better images than observatories were obtaining just 15 or 20 years ago. The fact is that state of the art professional work is routinely surpassed by amateurs with modest equipment. Not only

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    Figure 1-2: A wide-angle lens on a 35-mm camera is a powerful tool for recording large areas of the sky. Here, a 35-mm lens and hypered Kodak Technical Pan records all of Orion, including the semicircular nebula known as Barnard’s Loop and the pumpkin-like Lambda Orionis nebula at the “head” of Orion. The Rosette Nebula in Monoceros is to the left. Photo by Edward Szczepanski.

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    Figure 1-3: Simple star trails taken with an unguided, tripod-mounted camera will teach you about the characteristics of sky, the camera and lens, and the film used. Here, the stars circle Polaris over the Texas Star Party. This photo was taken with a 20-mm f/3.5 lens on Kodak Ektachrome Elite II 100. Photo by Robert Reeves.

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    that, amateurs are portable. They can travel to where the sky is clear, while professional observatories are anchored to one location.

    But if wide-field astrophotography is so simple, what is the purpose of the rest of this book? Like any endeavor, wide-field astrophotography has many levels. Amazing results can be achieved with simple equipment, but there is much more that can be accomplished with advanced techniques. The theory and practical application of these will comprise the majority of this text. The actual level of an individual’s involvement in this field is governed by one’s interest and available resources.

    1.3 How I Got Started I was inspired to begin celestial photography by a 1957 article in National Geographic Magazine about the then-ongoing Palomar Observatory Sky Survey (POSS) being conducted with the 48-inch Schmidt telescope there.

    The giant Schmidt produced negatives 14 inches square encompassing a field of view six degrees on a side. The detail recorded on these plates was astonishing. The infinite depth of space and the precision and beauty of the endless sweeping star vistas captured my imagination.

    Inspired by the Palomar images, I took my family’s WWII-vintage Voi- ghtlander camera to the roof of the garage, pointed it at the brightest star in the sky, braced it in place with blocks of wood, and snapped a one-second exposure of what I later learned was the planet Jupiter. Emboldened by this first step, I lengthened the exposures to a half-hour.

    When I saw the prints from that first roll of 120-format Verichrome Pan, I discovered, to my joy and astonishment, that my initial images had turned out well. With a maximum aperture of f/4.5, I had succeeded in recording Jupiter with that first one-second snap. In fact, seemingly hun- dreds of stars piled up on the longer-exposed negatives, and I could clearly trace the arcs of stars circling the celestial pole and identify the pattern of constellations as charted on star maps.

    The attraction the Milky Way holds for me was summed up quite nicely by Edward E. Barnard in the introduction to his classic work An Atlas of Selected Regions of the Milky Way:

    …the Milky Way reveals all its wonderful structure, which is so magnificent in photographs made with the portrait lens. The observer with the more powerful telescopes, and necessarily more restricted field of view, has many things to compensate h