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You can, of course, process film images with the same software that you use for DSLR images. Noise takes the form of random grain only; there is no fixed-pattern noise. Stacking multiple images builds contrast and reduces grain. First you have to get the film images (slides or negatives) into digital form. There are many methods. The best is a film scanner with a resolution of at least 2400 dpi (about 100 pixels/mm).
This chapter describes how to interpret published tests of DSLR sensors and how to test your own. We start by focusing on published tests. By the time you read this, the cameras tested here will not be the latest on the market, but they are good examples.
Digital imaging has narrowed the gap between professional and amateur astronomy. It is nowadays common for amateurs to photograph objects that are not very well known to science. We are no longer confined to just a few hundred prominent targets discovered centuries ago. Accordingly, we need to open up the professional astronomers’ kit of tools for identifying and researching celestial objects. The most important data sources are free on the Internet.
When I wrote the first edition of this book, I said that the time was not yet ripe for a comprehensive handbook of DSLR astrophotography. Now it is, and I have rewritten almost the entire book from scratch because so much has changed and so much more knowledge is available. And the torrent of new developments never stops. Please check this book’s web site, www.dslrbook.com, for updates and additional information immediately. Not everyone will read all the chapters of the book straight through. To cover such a complicated, technical subject, I have had to spiral outward through the subject matter, passing through several regions more than once.
Beyond the basics of image calibration, stacking, and gamma correction, many other techniques are also used to improve astronomical images. This chapter quickly surveys some of the most important. Several of the techniques in this chapter borrow a principle from artificial intelligence and machine vision: If human beings can see something in an image, it should be possible to program a computer to “see” the same thing.
Although some observing sites are blessed with AC power, most astrophotographers rely on batteries in the field. In fact I often use battery power even at home, both to make sure my field-trip equipment is working and for greater safety. Many of us also bring computers into the field, both for autoguiding and for camera control. This chapter surveys the use of batteries and electronic controls with astronomical equipment.
To take exposures longer than a few seconds, you must track the stars. That is, the telescope must compensate for the earth’s rotation so that the image stays in the same place on the sensor while the earth turns. This chapter covers the basics of using altazimuth and equatorial mounts, especially German equatorial mounts (GEMs).
Before going into the details of astrophotographic equipment, I need to outline how it is used. This chapter covers how to take pictures of deep-sky objects, including calibration frames. The actual processing and calibration are covered in Chapters 11–13, and lunar and planetary work, in Chapter 14.
Digital technology has revolutionized solar, lunar, and planetary imaging even more than deep-sky work. Amateurs with portable telescopes don’t just rival the best work done by observatories 50 years ago, they surpass it. Thanks to video imaging, we get planetary images better than anything that had been taken from earth before 1985 or so. Accordingly, this chapter addresses — at last — the sun, moon, and planets. The applicable techniques are such a vital part of astrophotography that they deserve coverage even if a DSLR is not always the ideal camera for practicing them.
This chapter covers camera settings and operation for astrophotography. In what follows, I’m going to assume that you have learned how to use your DSLR for daytime photography and that you have its instruction manual handy. No two cameras work exactly alike. Most DSLRs have enough in common that I can guide you through the key points of how to use them, but you should be on the lookout for exceptions.
This chapter outlines five simple ways to take an astronomical photograph. Each of them will result in an image that requires only the simplest subsequent processing by computer. All the projects in this chapter can be done with your camera set to output JPEG images (not raw), as in daytime photography. The images can be viewed and further processed with any picture processing program, such as Photoshop or GIMP (which is freeware). Special astronomical techniques are not needed.
The image sensor is the heart of the camera. The two things we most want to know about sensors are whether one camera is better than another, and what ISO setting works best with a given camera. This chapter and the next will explore sensor performance in detail.
How do you take a picture through a telescope? Any of numerous ways. This chapter covers the basic optical configurations as well as some (not all) ways of assembling the adapters. The most important thing to remember is that it’s not enough to make everything fit together mechanically; you must also consider the spacings between optical elements, and not all configurations work with all telescopes.