دانلود کتاب Digital SLR Astrophotography

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Contents Preface Part I DSLRs for Astrophotography 1 Welcome to DSLR Astrophotography 1.1 What is a DSLR? 1.1.1 Digital Single-Lens Reflex Cameras 1.1.2 DSLRs without Mirrors: MILCs 1.2 DSLRs versus Other Cameras 1.2.1 Dedicated Astrocameras 1.2.2 Fixed-Lens Digital Cameras? 1.2.3 What about Film? 1.3 Choosing a DSLR 1.3.1 Canon vs. Nikon vs. Others 1.3.2 Camera Features 1.3.3 Shopping Strategy 1.4 Choosing Software 1.5 Choosing the Computer 1.6 Choosing the Telescope or Lens 1.6.1 The Aperture Counterrevolution 1.6.2 The 500-mm Optimum 1.6.3 Ease of Use 1.7 Choosing the Mount 1.8 The Craft of Astrophotography 1.8.1 Building your Skill and Judging your Achievements 1.8.2 Pushing Limits or Staying within Them 1.8.3 Testing as a Means or an End 1.8.4 Philosophical and Ethical Issues 1.8.5 Amateur or Professional? 2 Digital Image Technology 2.1 What is a Digital Image? 2.1.1 Bit Depth 2.1.2 Linear or Gamma-corrected? 2.1.3 Color Encoding 2.1.4 The Alpha Channel 2.1.5 Frames 2.2 File Formats 2.2.1 File Size 2.2.2 Compression 2.2.3 Raw Files 2.2.4 dcraw and Adobe DNG 2.2.5 JPEG 2.2.6 TIFF 2.2.7 PNG 2.2.8 FITS 2.2.9 XISF 2.3 Color Imaging in Detail 2.3.1 The Bayer Matrix (CFA) 2.3.2 Low-pass Filtering 2.3.3 Nebulae are Blue or Pink, not Red 2.3.4 Color Balance (White Balance) 2.3.5 Gamut 2.4 Image Size and Resizing 2.4.1 Dots per Inch 2.4.2 Resampling 2.4.3 Binning 2.4.4 The Drizzle Algorithm 2.5 Histograms, Brightness, and Contrast 2.5.1 Histograms 2.5.2 Histogram Equalization 2.5.3 Curve Shape 2.5.4 Gamma Correction in Detail 2.6 Sharpening 2.6.1 Edge Enhancement 2.6.2 Unsharp Masking 2.6.3 Spatial Frequency and Wavelet Transforms 2.6.4 Multiscale Processing 2.6.5 Deconvolution 3 DSLR Operation 3.1 Taking a Picture Manually 3.1.1 Shutter Speed and Aperture 3.1.2 Manual Focusing 3.1.3 ISO Speed 3.1.4 Do You Want an Automatic Dark Frame? 3.2 Menu Settings 3.2.1 Things to Set Once and Leave Alone 3.2.2 Settings for an Astrophotography Session 3.3 How to See that Tiny Screen 3.4 More Features of the Camera Body 3.4.1 The Eyepiece Diopter 3.4.2 The Strap and Eyepiece Cover 3.4.3 Limiting Light Emission from the Camera 3.5 Tripping the Shutter without Shaking the Telescope 3.5.1 Self-timers and Remote Controls 3.5.2 Mirror Lock and Prefire 3.5.3 Electronic First-curtain Shutter (EFCS) 3.5.4 Other Tricks 3.5.5 Vibration-reducing Lenses 3.6 Focusing 3.6.1 Magnified Preview on the Screen 3.6.2 Stars and Spikes 3.6.3 Computer Focusing 3.6.4 Focusing Telescopes with Moving Mirrors 3.7 Other Image Quality Issues 3.7.1 Grain 3.7.2 Star Eaters 3.7.3 Dust on the Sensor 3.8 The Camera as Your Logbook 4 Five Simple Projects 4.1 Telephoto Moon 4.2 Afocal Moon 4.3 Stretching – The Processing Technique to Learn Now 4.4 Stars from a Fixed Tripod 4.5 Nightscapes 4.6 Piggybacking 4.7 Going Further Part II Equipment and Techniques 5 Deep-sky Image Acquisition 5.1 How to Avoid Most of This Work 5.2 How Long to Expose 5.3 Dithering 5.4 Taking Calibration Frames 5.4.1 Dark Frames 5.4.2 Flats 5.4.3 Flat Darks 5.4.4 Bias Frames 6 Coupling Cameras to Telescopes 6.1 Optical Configurations 6.1.1 Types of Telescopes 6.1.2 Newer Telescopes 6.1.3 Types of Coupling 6.2 Fitting it All Together 6.2.1 Types of Adapters 6.2.2 Sensor Position Matters 6.3 Optical Parameters 6.3.1 Focal Length 6.3.2 Aperture 6.3.3 f -Ratio and Image Brightness 6.3.4 Field of View 6.3.5 Sensor Size 6.3.6 Arc-seconds per Pixel 6.3.7 “What is the Magnification of This Picture?” 6.4 Edge-of-field Quality and Vignetting 7 Camera Lenses 7.1 Why You Need Another Lens 7.1.1 Big Lens or Small Telescope? 7.1.2 Field of View 7.1.3 f -Ratio 7.1.4 Zoom or Non-zoom? 7.2 Lens Quality 7.2.1 Sharpness, Vignetting, Distortion, and Bokeh 7.2.2 Reading MTF Curves 7.2.3 Telecentricity 7.2.4 Construction Quality 7.3 Which Lenses Fit Which Cameras? 7.3.1 Canon 7.3.2 Nikon 7.3.3 Lens Mount Adapters 7.3.4 What if there’s no Aperture Ring? 7.3.5 Adapter Quality 7.3.6 The Classic M42 Lens Mount 7.4 Supporting and Mounting a Lens 7.5 Testing a Lens 7.5.1 How to Test 7.5.2 Limitations of the Lens Design 7.6 Diffraction Spikes around the Stars 7.7 Understanding Lens Design 7.7.1 How Lens Designs Evolve 7.7.2 The Triplet and its Descendants 7.7.3 The Double Gauss 7.7.4 Telephoto and Retrofocus Lenses 7.8 Special Lenses 7.8.1 Macro Lenses 7.8.2 Mirror Lenses 7.8.3 Image Stabilization (Vibration Reduction) 7.8.4 Diffractive Optics 8 Tracking the Stars 8.1 Two Ways to Track the Stars 8.2 The Rules Have Changed 8.3 Types of Equatorial Mounts 8.3.1 Fork Mounts on Wedges 8.3.2 Sky Trackers 8.3.3 German Equatorial Mounts (GEMs) 8.4 Hardware 8.4.1 Dovetails 8.4.2 Counterweights 8.5 Setting up a Computerized Equatorial Mount 8.5.1 The Difference Between Polar and Go-to Alignment 8.5.2 Don’t Judge it by the First Star 8.5.3 Must You Level the Tripod? 8.5.4 Hints for Go-to Alignment 8.5.5 Go-to Alignment with just a Telephoto Lens 8.5.6 Using Go-to Alignment to Refine Polar Alignment 8.6 Classic Methods 8.6.1 Finding the Pole in the Sky 8.6.2 More about Polar Scopes 8.6.3 The Drift Method 8.6.4 Automated Drift Method 8.6.5 Why the Drift Method is Best 8.7 How Accurately Must We Polar-align? 9 Precision Tracking and Guiding 9.1 Why Telescopes Do not Track Perfectly 9.2 Must We Make Guiding Corrections? 9.2.1 Sometimes, no 9.2.2 A Futile Quest 9.3 Mount Performance 9.3.1 How Tracking Error is Measured 9.3.2 Periodic Gear Error 9.3.3 Backlash 9.3.4 Flexure 9.4 Periodic-error Correction (PEC) 9.5 Autoguiding 9.5.1 The Concept 9.5.2 Subpixel Accuracy 9.5.3 Communication with the Mount 9.5.4 Autoguiding Software 9.6 Cameras, Guidescopes, and Off-axis Guiders 9.6.1 The Guide Camera 9.6.2 Guidescopes 9.6.3 Off-axis Guiders 9.6.4 On-axis Guiding 9.7 Using an Autoguider 9.7.1 Choosing a Guide Star 9.7.2 Hot Pixels and Dark Frames 9.7.3 Calibration 9.7.4 Autoguider Settings 9.7.5 Algorithms 9.7.6 Quality of Guiding 9.7.7 Interpreting Guiding Graphs 9.7.8 Right Ascension and Declination are Different 9.7.9 PEC while Autoguiding? 9.7.10 Good Autoguiding, Bad Pictures 9.8 The Challenge of Round Star Images 9.8.1 What Should a Star Image Look Like? 9.8.2 How Roundness is Measured 9.8.3 Some Practical Tips 9.8.4 Downsampling 9.8.5 Deconvolution 10 Power and Camera Control in the Field 10.1 Portable Electric Power 10.1.1 Power for the Telescope 10.1.2 DC Power Connectors 10.1.3 Voltage 10.1.4 Powering the Computer and Camera 10.1.5 Care of Li-ion Batteries 10.1.6 Ground Loop Problems 10.1.7 Safety 10.2 Camera Control 10.2.1 How Camera Control is Done 10.2.2 Choosing a Laptop 10.2.3 Cables 10.2.4 Camera Control Software 10.3 Networking Everything Together 10.4 Operating at Very Low Temperatures Part III Image Processing 11 Deep-sky Image Processing 11.1 Processing Workflow 11.2 Calibration 11.2.1 Image Arithmetic 11.2.2 Components of a Raw Image 11.2.3 Master Darks, Flats, Flat Darks, and Bias Frames 11.2.4 Should Flats Be Binned or Smoothed? 11.2.5 Method 0: Just Lights and Darks 11.2.6 Method 1: Lights, Darks, Flats, and Flat Darks 11.2.7 Method 2: Lights, Darks, Flats, and Bias 11.2.8 Method 3: Lights, Darks, Flats, Flat Darks, and Bias 11.2.9 Scaling the Dark Frames 11.3 Cosmetic Correction 11.4 DeBayerization 11.5 Stacking 11.5.1 The Concept 11.5.2 Confusing Term: Integration 11.5.3 How Images Are Combined 11.6 Before We Stack, We Align 11.7 Nonlinear Stretching (Gamma Correction) 11.7.1 The Concept 11.7.2 Digital Development Processing (DDP) 11.8 Postprocessing 12 Workflow with Specific Software 12.1 Before We Start 12.1.1 Screen Stretch 12.1.2 Methods and ISO Settings 12.2 DeepSkyStacker 12.2.1 User Interface 12.2.2 Setting up 12.2.3 Calibrating and Stacking Images 12.2.4 Viewing and Selecting Images to Stack 12.2.5 Stretching 12.3 Nebulosity 12.3.1 User Interface 12.3.2 Basic File Editing 12.3.3 Calibration 12.3.4 DeBayering 12.3.5 Choosing Images to Stack 12.3.6 Aligning and Stacking Images 12.3.7 Stretching 12.4 MaxIm DL 12.4.1 User Interface 12.4.2 Basic File Editing 12.4.3 Choosing Images to Stack 12.4.4 Calibration and Stacking 12.4.5 Stretching 12.5 PixInsight 12.5.1 User Interface 12.5.2 Basic File Editing 12.5.3 Choosing Images to Stack 12.5.4 Raw or FITS? 12.5.5 Calibration and Stacking 12.5.6 Stacking (Integration) as a Separate Step 12.5.7 Stretching 12.5.8 PixInsight Workflow Summary 13 More Image Processing Techniques 13.1 Flattening the Background 13.1.1 The Concept 13.1.2 Subtract or Divide? 13.1.3 Linear or Gamma-corrected? 13.1.4 Nebulosity 13.1.5 MaxIm DL 13.1.6 PixInsight 13.2 Removing Noise 13.2.1 The Concept 13.2.2 Luminance vs. Chrominance 13.2.3 Linear or Gamma-corrected? 13.2.4 Nebulosity 13.2.5 MaxIm DL 13.2.6 PixInsight 13.3 Color Saturation 13.3.1 The Concept 13.3.2 Linear or Gamma-corrected? 13.3.3 Nebulosity 13.3.4 MaxIm DL 13.3.5 PixInsight 13.4 Masks 13.5 Who Moved? The Difference between Two Pictures 13.5.1 The Concept 13.5.2 Preparing the Images 13.5.3 PixInsight 13.5.4 MaxIm DL 13.5.5 Nebulosity 13.5.6 Photoshop 13.6 High Dynamic Range (HDR) 14 Sun, Moon, Eclipses, and Planets 14.1 Full-face Lunar and Solar Images 14.1.1 Optics and Field of View 14.1.2 Exposure 14.1.3 Tracking 14.1.4 Stacking 14.1.5 The Moon 14.1.6 The Sun 14.1.7 Eclipses, Solar and Lunar 14.2 High-resolution Video: How it’s Done 14.2.1 Overview of the Process 14.2.2 Acquiring the Images 14.2.3 How Long to Expose 14.2.4 Preparation and Stacking 14.2.5 Multiscale Sharpening 14.2.6 RGB Alignment 14.3 High-resolution Video: Technical Matters 14.3.1 Matching Focal Length to Pixel Size 14.3.2 Why High-resolution Video Works Part IV Advanced Topics 15 Sensor Performance 15.1 Generations of DSLRs 15.2 How Sensors Work 15.2.1 Photoelectrons 15.2.2 CCD and CMOS Sensors 15.2.3 What We Don’t Know 15.3 Sensor Performance Basics 15.3.1 Pixel Size 15.3.2 Quantization and DNs (ADUs) 15.3.3 Bias (Offset), Dark Clipping, and Compression 15.3.4 Linearity 15.3.5 ISO Speed Adjustment 15.3.6 Gain 15.3.7 Color Balance (White Balance) 15.3.8 The Anti-aliasing Filter 15.4 Image Flaws 15.4.1 Bad Pixels 15.4.2 Pixel Inequality 15.4.3 Blooming 15.4.4 Amplifier Glow (Electroluminescence) 15.4.5 Cosmic Rays 15.4.6 Degradation with Age 15.5 Noise, in Detail 15.5.1 What Noise Is 15.5.2 Signal-to-noise Ratio (SNR) 15.5.3 Shot Noise 15.5.4 Read Noise 15.5.5 Dark Current (Thermal Noise) 15.5.6 Chrominance Noise 15.5.7 Effect of Stacking, Binning, and Downsampling 16 Testing Sensors 16.1 ISO Invariance 16.2 True ISO Speed 16.3 Dynamic Range 16.4 Noise Analysis 16.5 Quantum Efficiency and Other Parameters 16.6 Obtaining Data from Your Own Sensor 16.6.1 Overview 16.6.2 PixInsight 16.6.3 MaxIm DL 16.7 Specific Tests 16.7.1 Dynamic Range from One Light Frame and One Flat Dark 16.7.2 Read Noise in DN from Two Flat Darks or Bias Frames 16.7.3 Gain in DN/e−from a Pair of Generously Exposed Flats 16.7.4 Read Noise Measured in Electrons 16.8 Going Further 17 Spectral Response and Filter Modification 17.1 DSLR Spectral Response 17.2 Filter Modification 17.2.1 What Filter Modification Achieves 17.2.2 Is Filter Modification Necessary? 17.3 Filters to Cut Light Pollution 17.3.1 How Light Pollution can be Removed 17.3.2 Filters to Favor Nebulae 17.3.3 The Middle Ground 17.4 How Filters Are Made 17.4.1 Dye Filters 17.4.2 Interference Filters 17.4.3 Didymium Glass 17.4.4 Precautions 18 Tools for Astronomical Research 18.1 Star Maps 18.2 Simbad, Aladin, and VizieR 18.3 Case Study: An Unnamed Nebula in Monoceros 18.4 Plate Solving for Identification and Position 18.5 Case Study: Have I Discovered a Star Cluster? 18.6 Variable-star Photometry 18.6.1 Acquiring Images 18.6.2 Aperture Photometry 18.6.3 Photometry Software 18.6.4 Example: Light Curve of EH Librae 18.7 Asteroid or Nova? 18.8 Research Literature On Line Part V Appendices A Digital Processing of Film Images B Exposure Tables B.1 Sun B.2 Moon B.3 Planets B.4 Deep-sky Objects B.5 How Exposures are Calculated Index