Introduction

It is always humbling to consider the great achievements of the ancients, who made their discoveries without access to today’s technology.

Astronomy is such a fascinating subject that I like to think that astrophotography is more than just making pretty pictures. For my own part, I started both at the same time and I quickly realized that my knowledge of astronomy was deficient in many areas. Reading up on the subject added to my sense of awe and also made me appreciate the dedication of astronomers and their patient achievements over thousands of years. A little history and science is not amiss in such a naturally technical hobby. Incredibly, the science is anything but static; in the intervening time since the last book, not only has the general quality of amateur astrophotography improved greatly, but we have sent a probe 6.5 billion km to land on a comet traveling at 65,000 km/h and found firm evidence of water on Mars. In July 2015 the New Horizons space probe, launched before Pluto was downgraded to a minor planet, grazed past the planet 12,000 km from its surface after a 9.5 year journey of 5 billion km. (It is amazing to think that its trajectory was calculated using Newton’s law of universal gravitation, published in 1687.)

From the earliest days of human consciousness, mankind has studied the night sky and placed special significance on eclipses, comets and new appearances. With only primitive methods, they quickly realized that the position of the stars, the Moon and the Sun could tell them when to plant crops, navigate and keep the passage of time. Driven by a need for astrology as well as science, their study of the heavens and the belief of an Earth-centric universe was interwoven with religious doctrine. It took the Herculean efforts of Copernicus, Galileo and Tycho, not to mention Kepler, to wrest control from the Catholic Church in Europe and define the heliocentric solar system with elliptical orbits, anomalies and detailed stellar mapping.

Astronomers in the Middle East and in South America made careful observations and, without instruments, were able to determine the solar year with incredible accuracy. The Mayans even developed a sophisticated calendar that did not require adjustment for leap years. Centuries later, the Conquistadors all but obliterated these records at a time when ironically Western Europe was struggling to align their calendars with the seasons. (Pope Gregory XIII eventually proposed the month of October be shortened by 10 days to re-align the religious and hence agricultural calendar with the solar (sidereal) year. The Catholic states complied in 1583 but others like Britain delayed until 1752, by which time the adjustment had increased to 11 days!)

fig.1a An abbreviated time-line of the advances in astronomy is shown above and is continued in fig.1b. The achievements of the early astronomers are wholly remarkable, especially when one considers not only their lack of precision optical equipment but also the most basic of requirements, an accurate timekeeper

fig.1b Astronomy accelerated once telescopes were in common use, although early discoveries were sometimes confused by the limitations of small aperture devices.

The invention of the telescope propelled scholarly learning, and with better and larger designs, astronomers were able to identify other celestial bodies other than stars, namely nebula and much later, galaxies. These discoveries completely changed our appreciation of our own significance within the universe. Even though the first lunar explorations are over 45 years behind us, very few of us have looked at the heavens through a telescope and observed the faint fuzzy patches of a nebula, galaxy or the serene beauty of a star cluster. To otherwise educated people it is a revelation when they observe the colorful glow of the Orion nebula appearing on a computer screen or the fried-egg disk of the Andromeda Galaxy taken with a consumer digital camera and lens.

This amazement is even more surprising when one considers the extraordinary information presented on television shows, books and on the Internet. When I have shared back-yard images with work colleagues, their reaction highlights a view that astrophotography is the domain of large isolated observatories inhabited with nocturnal Physics students. This sense of wonderment is one of the reasons why astrophotographers pursue their quarry. It reminds me of the anticipation one gets as a black and white print emerges in a tray of developer. The challenges we overcome to make an image only increase our satisfaction and the admiration of others, especially those in the know. When you write down the numbers on the page, the exposure times, the pointing accuracy and the hours taken to capture and process an image, the outcome is all the more remarkable.

New Technology

The explosion of interest and amateur ability fuels the market place and supports an increasing number of astrobased companies. Five years on after writing the first edition, the innovation and value engineering continue to advance affordable technology in the form of mechanics, optics, computers, digital cameras and in no small way, software. The digital sensor was chiefly responsible for revolutionizing astrophotography but it itself is now at a crossroads. Dedicated imaging cameras piggy-back off the sensors from the digital camera market, typically DSLRs. At one time CCDs and CMOS sensors were both used in abundance. Today, CMOS sensors dominate the market place and are the primary focus of sensor development, increasing in size and pixel density. Their pixel size, linearity and noise performance are not necessarily ideal for astrophotography. New CCDs do emerge from Sony but these are a comparative rarity and are typically smaller than APS-C. It will be interesting to see what happens next; it may well drive a change in telescope optics to move to small field, shorter focal length and high resolution imaging. At the same time, the CCD sensor in my QSI camera has become a teenager.

It was not that long ago that a bulky Newtonian reflector was the most popular instrument and large aperture refractors were either expensive or of poor quality and computer control was but a distant dream. The increasing market helps to make advanced technology more affordable or downsize high-end features into smaller units, most noticeably in portable high-performance mounts and using the latest manufacturing techniques to produce large non-spherical mirrors for large reflector telescopes.

At the same time computers, especially laptops, continue to reduce in price and with increased performance and battery life. Laptops are not necessarily ideal for outdoor use; many are switching to miniature PCs (without displays or keyboards) as dedicated controllers, using remote desktop control via network technologies. New software required to plan, control, acquire and process images is now available from many companies at both amateur and professional levels. Quite a few are free, courtesy of generous individuals. At the same time, continued collaboration on interface standards (for instance ASCOM weather standards) encourages new product development, as it reduces software development costs and lead-times. If that was not enough, in the last few years, tablet computing and advanced smart phones have provided alternative platforms for controlling mounts and can display the sky with GPS-located and gyroscopically-pointed star maps. The universe is our oyster.

Scope of Choice

Today’s consumer choice is overwhelming. Judging from the current rate of change, I quickly realized that it is an impossible task to cover all equipment or avenues in detail without being variously out of date at publishing. Broad evaluations of the more popular alternatives are to be found in the text but with a practical emphasis and a process of rationalization; in the case of my own system, to deliver quick and reliable setups to maximize those brief opportunities that the English weather permits. My setup is not esoteric and serves as a popular example of its type, ideal for explaining the principles of astrophotography. Some things will be unique to one piece of equipment or another but the principles are common. In my case, after trying and using several types of telescope and mount, I settled on a hardware and software configuration that works as an affordable, portable solution for deep sky and occasional planetary imaging. By choosing equipment at the upper end of what can be termed “portable”, when the exertion of continual lifting persuaded me to invest in a permanent observatory, I was able to redeploy all the equipment without the need for upgrading. Five years on, astronomy remains a fascinating subject; each image is more than a pretty picture as a little background research reveals yet more strange phenomena and at a scale that beggars the imagination.

fig.2 A time-line for some of the key events in astrophotography. It is now 30 years since the first digital astrophotograph was taken and I would argue that it is only in the last 5 years that digital astrophotography has really grown exponentially, driven by affordable hardware and software. Public awareness has increased too, fuelled by recent events in space exploration, documentaries and astrophotography competitions.

About This Book

I wrote the first edition with the concept of being a fast track to intermediate astrophotography. This was an ambitious task and quite a challenge. Many astrophotographers start off with a conventional SLR camera and image processing software like Photoshop®. In the right conditions these provide good images. For those users there are several excellent on-line and published guides that I note in the bibliography. It was impossible to cover every aspect in detail, limited by time, page count and budget. My aim in this book is to continue where I left off: covering new ideas, advanced image processing, more advanced practical projects and fresh practical examples that cover new ground. This book is firmly focused on deep-sky imaging; my own situation is not ideal for high magnification work and any references to planetary imaging are made in passing.

The book is divided into logical sections as before: The first section covers the basics of astronomy and the limitations of physics and the environment. The second section examines the tools of the trade, brought up to date with new developments in hardware and software, including remote control, automation and control theory. The third section continues with setting up and is revised to take advantage of the latest technology. In the following section we do the same for image capture, looking at developments in process automation, guiding, focusing and mosaics.

The PixInsight content in the first book was very well received and several readers suggested I write a PixInsight manual. I am not a guru by any means and it would take many years of work to be confident enough to deliver an authoritative tome. Writing for me is meant to be a pleasure and the prospect of a software manual is not terribly exciting to either write, or I suspect, to read. Bowing to this demand, however, the image calibration and processing section provides further in-depth guides to selected processes in PixInsight and additionally uses PixInsight to process the new practical imaging assignments.

The assignments section has been revised and expanded: A couple of case studies have been removed, including the solitary planetary example. Some specialize in this field and they are best suited to expand on the extreme techniques required to get the very best imaging quality at high magnifications. As before, each case study considers the conception, exposure and processing of a particular object that, at the same time, provides an opportunity to highlight various unique techniques.

A worked example is often a wonderful way to explain things and these case studies deliberately use a variety of equipment, techniques and software. More recently these use my software of choice, namely Sequence Generator Pro, PHD2, PixInsight and Photoshop. The subjects are typically deep-sky objects that present unique challenges in their acquisition and processing. Practical examples are even more valuable if they make mistakes and we learn from them. Some examples deliberately include warts and present an opportunity to discuss remedies.

On the same theme, things do not always go to plan and in the appendices before the index and resources, I have updated the chapter on diagnostics, with a small gallery of errors to help with your own troubleshooting. Fixing problems can be half the fun but when they resist several reasoned attempts, a helping hand is most welcome. In my full-time job I use specialized tools for root-cause analysis and I share some simple ideas to track down gremlins. Astrophotography and astronomy in general lends itself to practical invention and not everything is available off the shelf. To that end, new practical projects are included in the appendices as well as sprinkled throughout the book. These include a comprehensive evaluation of collimation techniques for a Ritchey Chrétien telescope and ground-breaking chapters on designing and implementing an observatory controller, its ASCOM driver and a Windows Observatory controller application. It also includes a chapter on setting up a miniature PC as an imaging hub, with full remote control.

As in the first edition, I have included a useful bibliography and a comprehensive index. For some reason bibliographies are a rarity in astrophotography books. As Sir Isaac Newton once wrote, “If I have seen further it is by standing on the shoulders of Giants.” The printed page is not necessarily the best medium for some of the resources and the supporting website has downloadable versions of spreadsheets, drawings, program code, videos and tables, as well as any errata that escaped the various editors. They can be found at:

www.digitalastrophotography.co.uk


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