Digital SLR Astrophotography

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