Astrophotography
Thierry Legault
Language: English
Pages: 240
ISBN: 1937538435
Format: PDF / Kindle (mobi) / ePub
Today's photographic equipment allows amateurs to take pictures of the stars that far surpass images taken just a few decades ago by even the largest observatories-and this book will teach you how.
Author and world-renowned astrophotographer Thierry Legault teaches the art and techniques of astrophotography: from simple camera-on-tripod night-scene imaging of constellations, star trails, eclipses, artificial satellites, and polar auroras to more intensive astrophotography using specialized equipment for lunar, planetary, solar, and deep-sky imaging. Legault shares advice on equipment and guides you through techniques to capture and process your images to achieve spectacular results.
Astrophotography provides the most thorough treatment of the topic available. This large-format, richly illustrated book is intended for all sky enthusiasts-newcomers and veterans alike.
Learn how to:
- Select the most useful equipment: cameras, adapters, filters, focal reducers/extenders, field correctors, and guide telescopes
- Set up your camera (digital, video, or CCD) and your lens or telescope for optimal results
- Plan your observing sessions
- Mount the camera on your telescope and focus it for razor-sharp images
- Polar-align your equatorial mount and improve tracking for pin-point star images
- Make celestial time-lapse videos
- Calculate the shooting parameters: focal length and ratio, field of view, exposure time, etc.
- Combine multiples exposures to reveal faint galaxies, nebulae details, elusive planetary structures, and tiny lunar craters
- Adjust contrast, brightness, light curves, and colors
- Postprocess your images to fix defects such as vignetting, dust shadows, hot pixels, uneven background, and noise
- Identify problems with your images and improve your results
Optical Astronomical Spectroscopy (Series in Astronomy and Astrophysics)
Universe: The Definitive Visual Guide
Adventures into Space: The laugh out loud space comedy
Spacewalker: My Journey in Space and Faith as Nasa's Record-Setting Frequent Flyer
and OIII (assigned to blue) lines are rebalanced over Hα. Skillful amateurs separate the stars from the nebulae (by selection in Photoshop) and apply different color coefficients to each part before merging them, leading to more realistic stars colors. PROCESSING, REALISM, AND AESTHETICS Typically, processing a planetary image consists of trying to make an image that’s as close as possible to what is visually perceived through the telescope, possibly with a higher contrast to give a better view
the noise can mask low-contrast details or even be confused with true details. In a color image, where each color layer has its own noise, the result is a patchwork of small color dots. In all cases, it is an artifact that alters the accuracy and beauty of the image, like background clicks in a poor hi-fi sound system. The Sources of Noise Schematically, noise can be associated with each signal. This noise alters the corresponding signal and prevents it from being perfectly reproduced. It can
brightened with the help of curves or levels adjustments. Another method consists of using selections and layers to combine two images of different exposure time, one for the prominences and one for the disk. The general principle is to copy the image with the prominences as a layer on top of the image of the disk and to erase (with the eraser or the color range selection) the overexposed central part of the top layer. The main challenge is to obtain a transition between the disk and prominences
so it’s therefore more difficult to manufacture and to collimate. The Hubble Space Telescope is of this type. The advantage of this design is the elimination of coma, leaving only a bit of astigmatism and, above all, field curvature. Offering the best off-axis correction of the Cassegrain family, Ritchey-Chrétiens are particularly recommended for deep-sky imaging with large sensors, and of course with a field flattener. Companies such as Optical Guidance Systems (OGS), PlaneWave, Officina
minutes; that’s enough time for the sun or moon to move by one diameter. The angular speed decreases closer to the celestial pole, 10″ per second at a declination of 50° and 5″ per second at 70°. Refer again to the table on page 3, and let’s consider an example of a 20mm lens mounted on an APS-C DSLR. The angular field of view is 40° × 60°. If the sensor array is composed of 16 megapixels, the image measures about 3300 × 5000 pixels. Simple division reveals that each pixel subtends an angle of
