Basic Astrophotography for Beginners

Table of Contents

BASIC ASTROPHOTOGRAPHY.

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 several 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; new discoveries are being made all the time and an on-going examination of the Martian surface may reveal secrets that cause us to reevaluate extraterrestrial life.

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!).

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 40 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.

The explosion of interest and the ability of amateurs has been fuelled by the availability of if not new then certainly applied affordable technology in mechanics, optics, computers, digital cameras and in no small way, software. Of these, the digital sensor is chiefly responsible for revolutionizing astrophotography.

Knowledge is another essential ingredient and the ingenuity and shared experience through the Internet, rapidly contributing to the recent advancement of amateur astrophotography. 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.

Computer control was but a distant dream. In the last few years however, Far east manufacturing techniques have lowered the cost of high-quality optical cells, mirrors and motor-driven mounts. Several U.S. companies have taken alternative folded designs, using mirror and lens combinations, and integrated them with computer-controlled mounts to make affordable, compact, high-performance systems.

The same market forces have lowered the price of digital cameras and the same high-quality camera sensors power dedicated cameras, optimized with astrophotography in mind to push the performance envelope further. At the same time computers, especially laptops, continue to reduce in price and with increased performance too, including battery life.

The software required to plan, control, acquire and process images is now available from several companies at amateur and professional level and from not a few generous individuals who share their software free or for a nominal amount. At the same time, collaboration on interface standards (for instance ASCOM) 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.

Getting started with astrophotography.

Amateur astrophotography can be an end in itself or a means of scientific research and in some cases, a bit of both. It might be a surprise for some, but amateur astronomers, with differing degrees of patronage, have significantly contributed to our understanding of the universe, in addition to that from the scientific institutions. As an example, Tom Boles in Suffolk, England has identified over 124 supernova with his private observatory; these brief stellar explosions are of scientific importance and their spectra help determine the size and expansion of the universe.

Tom Boles. Supernova discoverer. Radio Suffolk 2011.

Video by Martin Mobberley

The professional large observatories cannot cover the entire sky at any one time and so the contribution from thousands of amateurs is invaluable, especially when it comes to identifying transient events. I might chance upon something in my lifetime but I have less lofty goals in mind as I stand shivering under a mantle of stars.

Astrophotography is not one hobby but many: There are many specialities and individual circumstances, as well as purpose. Depending on viewing conditions, equipment, budget and available time, amateur astronomers can vary from occasional imagers using a portable setup, to those with a permanent installation capable of remote control and operational at a moment’s notice.

The subjects too are just as numerous; from high magnification planetary and deep space imaging, though medium and wide-field imaging in broad or selective wavelengths. Then there is lunar and solar photography as well as environmental astrophotography, which creates wonderful starry vistas. As with any hobby, there is a law of diminishing returns and once the fundamentals are in place, further enhancements often have more to do with convenience and reliability than raw performance.

Lunar imaging.

The Moon is the most obvious feature of the night sky and easily passed over for more sexy objects. Several astronomers, including the late Sir Patrick Moore, specialized in lunar observation and photography. Being a large and bright object, it does not mandate extreme magnifications or an expensive cooled CCD camera. Many successful lunar photographs use a modest refractor telescope and a consumer CCD-based webcam adapted to fit into the eyepiece holder.

The resultant video image jumps around the screen and many frames are blurred. The video is only the starting point; subsequent processing discards the blurred frames and the remainder are aligned and combined to make a detailed image. Increasingly, digital SLRs are used for lunar photography, either in the increasingly popular video modes or as individual still frames at high shutter speeds.

The unique aspect of the Moon, and to some extent some planets too, is that their appearance changes from night to night. As the Moon waxes and wanes, the interesting boundary between light and shade, the terminator, moves and reveals the details of a different strip of the lunar surface. No two nights are precisely the same.

Planetary imaging.

The larger and brighter planets, Jupiter, Saturn, Venus and to a lesser extent Mars, have very similar challenges to that of lunar imaging. These bright objects require short exposures but with more magnification, often achieved with the telescope equivalent of a tele-converter lens. A converted or dedicated webcam is often the camera of choice in these situations since its small chip size is ideally matched to the image size.

Some use digital SLRs but the larger sensors do create large video files and only at standard video frame rates between 24 frames per second (fps) and 60 fps.

I have made pleasing images of Jupiter and Mars using a refractor with a focal length of just over 900 mm combined with a high-quality 5x tele-converter and an adapted webcam. The smaller and more distant planets are more challenging still, since not only are they are more difficult to locate but amateur equipment typically will render them as a simple blob.

These require more magnification, and as the magnification increases, so does the effect of vibration, tracking errors, focus errors and most significantly, atmospheric effects. The work of Damian Peach sets the standard for amateur imaging.

Solar imaging.

Solar imaging is another rewarding activity, especially during the summer months, and provided it is practiced with extreme care, conventional telescopes can be employed using a purpose-designed solar filter fitted to the main and guide scope. Specialist solar scopes are also available which feature fine-tuned filters to maximize the contrast of the Sun’s surface features and prominences. The resulting bright image can be photographed with a high-speed video camera or a still camera.

Solar Imaging . Equipment and Capture.

https://www.youtube.com/watch?v=AB1z_T5Y1ho

Video by Houston Haynes

Large Deep Space Objects.

One of the biggest surprises I had when I first started imaging was the enormous size of some of the galaxies and nebulae; I thought the Moon was the biggest object in the night sky. With a dark sky one can just make out the center of the Andromeda Galaxy with the naked eye but the entire object spans six times the width of our Moon, It is interesting to ponder what ancient civilizations would have made of it had they perceived its full extent.

These objects are within the grasp of an affordable short focal-length lens in the range 350-500 mm. The lower image magnification makes accurate star tracking less critical and even in light polluted areas, it is possible to use special filters and reduce the effect of the ever-present sodium street light. Successful imagers use dedicated CCD cameras or digital SLRs, either coupled to the back of a short telescope or with a camera telephoto lens. Typically, the camera system fits to a motorized equatorial mount and individual exposures range from a few 10s of seconds to 20 minutes.

Short focal length telescopes by their nature have short lengths and smaller diameters with correspondingly lightweight focus tubes. The technical challenges associated with this type of photography include achieving fore-aft balancing and the performance of the focus mechanism and tube as a result of a heavy camera hanging off its end. If you live under a regular flight path, the wide field brings with it the increased chance of plane trails across your images.

Small Deep Space Objects.

The smaller objects in the night sky require a longer focal length to make meaningful images, starting at around 800 mm. As the magnification increases, the image brightness reduces, unless the aperture increases at the same rate. This quickly becomes a lesson in practicality and economics.

Affordable refractor telescopes at the time of writing have typically a 5-inch or smaller aperture and at the same time, reflector telescopes have between 6- and 10-inch apertures.

Larger models do exist, to 16 inches and beyond, but come with the inherent risk of an overdraft and a hernia. The longer exposures required for these highly magnified objects benefit from patience, good tracking and a cooled CCD camera. At higher magnifications, the effects of atmospheric turbulence are noticeable and is often the weakest link in the imaging chain.

Environmental imaging.

This is for those shots that are astronomy-related but typically involve the surrounding landscape. Examples include images of the Northern Lights or a wide-field shot of the Milky Way overhead. Long exposures on a stationary tripod show the customary star trails, but shorter exposures with a wide-angle lens can render foreground and stars sharply at the same time.

Digital SLRs and those compacts with larger sensors make ideal cameras for these applications and a great place to start with no additional cost. At a dark field site, a panorama of the Milky Way makes a fantastic image.

Other activities.

Spectroscopic analysis, supernova hunting, asteroid, minor planet, comet and satellite tracking are further specializations for some astrophotographers. Supernova hunting requires a computer-controlled mount directing a telescope to briefly image many galaxies each night, normally using a programmed sequence. Each image in turn is compared with prior images of the same object. The prize is not a pretty image but the identification of an exploding star.

Each of these specialities have interesting technical challenges associated with object location, tracking and imaging. For instance, on Atlantis’ last flight it docked with the International Space Station. Thierry Legault imaged it with a mobile telescope as it transited the Sun. The transit time was less than a second and he used a digital SLR, operating at its top shutter speed and frame rate to capture a sequence of incredible images, paparazzi-style.