The amazing color images of deep-sky astronomical objects that we see in books and magazines are made possible by the magic of long-exposure astrophotography. Besides capturing what we can see with our unaided eyes, astrophotography allows us to take pictures of astronomical objects with colors that can not be seen at all visually through a telescope because they are too faint.

Astrophotography's incredible power to fuel the human imagination, as well as scientific discovery, comes from the fact that photographs can record photons of light over time and record images and details that are otherwise invisible.

Astrophotography began more than 150 years ago when images of astronomical objects were taken with one of the earliest photographic technologies, the Daguerreotype. Later inventions of different technologies, such as spectroscopic emulsions and gas-hypersensitization, led to constant improvement in film-based astrophotography. Film ruled the world of astronomical photography for more than 100 years until the coming of digital sensors in the later part of the 20th century.

Black and white CCD cameras started the initial digital revolution, first in professional observatories and then in advanced amateur astrophotography. Today all professional scientific astronomical photography is done with solid-state silicon-based sensors in CCD cameras.

Recently these silicon sensors have started another revolution, this time in amateur and professional photography with DSLR cameras. Although these sensors are still black and white devices, very clever tricks are employed to create excellent color images in just a single exposure.

These digital cameras count photons of light from stars, nebulae and galaxies, and turn these counts into numbers that we can work with in our computers.

DSLRs are better than their predecessor film SLR cameras for long-exposure deep-sky imaging because of their superior quantum efficiency (the percentage of photons that strike the sensor that actually get counted), lower noise and higher resolution. They are much less expensive and more versatile than their astronomical CCD camera cousins because they can also be used for regular daytime photography. The interchangeable lenses that are offered as part of these camera's systems can be used to take wide-angle portraits of constellations and the Milky Way, and fast long-focal length telephotos can shoot larger objects in the sky. The lenses can easily be removed and the camera can be hooked up to a telescope to shoot close ups of smaller celestial objects.

With the single-shot color digital sensors available today, astrophotographers can take images that rival those taken with much more expensive dedicated CCD astronomical cameras. Rapid advances in DSLR cameras have led to significant improvements in the technology with a new generation of improved DSLR cameras being produced every year or two.

We will briefly touch on other kinds of digital cameras that are available, such as digital snapshot cameras (DSC) with non-removable lenses, astronomical CCD cameras, and webcams, but we won't go into the specifics about how to do astrophotography with these kinds of cameras. We will discuss, in detail, the kinds of astrophotography that can be done with DSLR cameras, including long-exposure deep-sky astrophotography. Planetary photography is not discussed in depth because it can be done much better with inexpensive webcams. This book is primarily about astrophotography with DSLR cameras.

Getting Started

To get started in DSLR astrophotography, you really don't need much more than a DSLR camera and lens and a tripod. More advanced work requires an equatorially mounted telescope that is accurately polar aligned.

For astronomical image processing, you will need a computer and image processing software. Commercial software specifically dedicated to the processing of DSLR astronomical images is available such as Images Plus, MaxIm DL and PixInsight. Freeware programs are also available such as DeepSky Stacker, and Christian Buil's IRIS, although IRIS' graphical interface is quirky and its full power requires use of a command line.

Most astrophotographers also use regular image processing software such as Adobe^® Photoshop^® for final adjustments to the color and contrast of their images. Freeware programs such as the GNU Image Manipulation Program (GIMP) are also available for this purpose.

For basic processing of JPEG images, we will do all of our processing in Photoshop. Photoshop^® Elements^® can also be used although some things are labeled slightly differently or located in different locations in Elements. Other image processing programs such as Paint Shop Pro^®, or Picture Window can also be used. The basic procedures are the same.

For advanced processing of raw images, we will calibrate, align, and stack in Images Plus, and then adjust and enhance the images in Photoshop. Most of the procedures for advanced image adjustments can also be done in Photoshop Elements and other programs, although some tools, such as layer masks, may require some tricks or third party actions or plug-ins. Step-by-step instructions for calibration and stacking in Images Plus, and image adjustment and enhancement in Photoshop are given here, but the specifics of working with other programs are not covered.

Raw images can be converted in the image processing programs that come with the particular camera you buy, such as Canon's Digital Photo Professional^®, and Nikon's Nikon View^®, however you cannot do any type of astronomical image calibration or advanced image processing in these programs.