The Deep-Sky Imaging Primer by Charles Bracken

Over ten thousand people got their start in astrophotography with the first two editions, now The Deep-sky Imaging Primer has been fully revised and expanded in this new third edition. It has been updated to include the latest cameras, technology, and software. Everything you need to know about capturing and processing stunning images of deep-sky objects is covered:

• The fundamental principles of electronic cameras, optics, and mounts
• How to choose the best camera and telescope for you
• How to set up, choose exposure parameters, and take the images
• Where and when to find the best deep-sky objects
• How to process images—in addition to PixInsight® and Adobe Photoshop®, Affinity Photo® and AstroPixelProcessor® are now fully covered

Start-to-finish examples of image processing are included, with a focus on PixInsight. The book is 280 pages with 373 illustrations, printed in full-color.

Welcome to Astrophotography!    7

Section 1: Understanding Images

1. Electronic sensors
   • The challenges of deep-sky imaging 9
   • How electronic sensors work                   9
   • Sensor architecture: CCD vs CMOS      10
   • Well capacity and bit depth   11
   • The trade-off between dynamic range and gain              11
   • The importance of bit depth 13
   • Linear data and response curves          13
   • Creating color images                14
2. Signal and Noise
   • How signal varies       16
   • Signal and noise at the pixel level        17
   • Shot noise    18
   • An example of shot noise        19
   • A dimmer example   22
   • Skyglow        22
   • Why shot noise cannot be subtracted away    23
   • Dark current                   24
   • Read noise   25
   • Adding signals and noise        26
   • Variation in two-dimensions                    27
   • Bringing it all together              27

Section 2: Acquiring Images

3. Choosing and using a mount
   • Types of mounts                  31
   • Choosing and using a GEM              33
   • Meridian flip        33
   • Polar alignment 34
   • Drift alignment 35
   • Impact of polar alignment error on tracking            35
   • Tracking error     36
   • Balancing a mount             37
4. Choosing a camera
   • DSLRs    38
   • Dedicated astronomical cameras                  38
   • Parameters to consider in choosing a camera         39
   • The CMOS revolution       39
   • Sensor size and field of view          39
   • Parameters of common sensors  40
   • Connecting your camera to a telescope   42
5. Image scale: matching sensor and optics
   • Resolution and seeing     43
   • Sampling               45
   • Factors that limit resolution          46
   • Equipment recommendations     48
   • Focal reducers and field flatteners               48
   • Finding the right flattener or reducer        49
   • Understanding the ‘f-ratio myth’ debate 50
   • Etendue and comparing optical systems 50
6. Choosing a telescope
   • Fundamental optical parameters                  52
   • Telescopes for visual vs. imaging use         52
   • Optical aberrations            52
   • The Strehl ratio 54
   • Refractors              54
   • Telephoto lenses                 56
   • Reflectors and compound telescopes        56
   • Summary of telescope options    59
7. Filters and narrowband imaging
   • Filters for imaging             60
   • Choosing the right filter size          60
   • Narrowband filters             61
   • Light pollution filters       63
   • DSLR filters and modification       64
8. Focusing and setting up
   • Focusing                 65
   • Achieving critical focus  65
   • Reducing setup time        66
   • Dovetails, rings, and other mount accessories       67
   • Threaded connections    67
   • Power supplies  68
   • Dew prevention                    68
   • USB cables and hubs         68
9. Automating image acquisition
   • Automating your imaging               69
   • Connecting to the mount                 70
   • ASCOM, Alpaca, and INDI                 70
   • Choosing and setting up a control PC         71
10. Autoguiding
    • Autoguiding fundamentals            73
    • Autoguiding software     74
    • Guiding graphs and performance                 76
11. Setting exposure parameters
    • Principles of choosing subexposure duration         78
    • Subexposure duration: the histogram method      79
    • Subexposure duration: the calculated method     79
    • Setting gain         82
12. Taking the exposures
    • Planning for a night of imaging  84
    • A basic image capture workflow 85
    • A review of calibration frames     85
    • Taking dark frames            87
    • Taking flat frames               87
    • How many flats should you take?                  88
    • Taking bias frames             88
    • Do I really need to take calibration frames?              89
    • Dithering light frames     89
13. Choosing objects to image
    • The size of deep-sky objects          90
    • The deep-sky catalogs    90
    • Object types and the seasons        91
    • A survey of object sizes  94
    • Giant Objects (2° or greater)           94
    • Really Big Objects (1–2°)                    94
    • Objects from 30–60’          94
    • Objects from 15–30’          95
    • Objects from 5–15’             95
    • Objects from 1–5’                95
    • Objects smaller than 1’   95
14. The Sun, the Moon, and the atmosphere
    • When is it dark enough? 96
    • Light pollution  96
    • Measuring sky brightness                98
    • Impact of the moon           98
    • Impact of object altitude                  99
    • Local turbulence                  101
15. Improving your results
    • The astrophotography learning curve       102
    • Getting more data              102
    • Getting better SNR from your raw data     102
    • Getting better resolution                 103
    • Getting more out of your data in processing            103

Section 3: Processing Images

16. Color in digital images
    • Raw data and image file formats                    105
    • How we perceive color    105
    • Producing color on print and screen           105
    • Color management and color spaces          107
    • LAB color                108
    • The HSL/HSV/HSB color model    108
    • White balance and color temperature       108
    • Deep-sky color accuracy 109
    • Color calibration with stellar spectra          109
17.  Image processing applications
    • The stages of image processing  110
    • Choosing among image processing applications 110
18. Using Pixinsight
    • PixInsight’s learning curve              112
    • The PixInsight user interface         112
    • Working with images in PixInsight               114
    • Working with processes in PixInsight        117
    • Image and process containers      118
    • ScreenTransferFunction 118
19. Layers and selections in Photoshop and Affinity Photo
    • Layers   120
    • Layer blending modes    121
    • Composite layers                 121
    • Working with filters non-destructively     122
    • Selections and feathering                123
20. Fundamentals of pre-processing
    • Throwing out problem shots         124
    • The types of calibration frames   124
    • Pre-processing overview                  125
    • Creating master calibration frames             125
    • Dark scaling         125
    • Registration: aligning the calibrated subframes   127
    • Normalization   127
    • Integration methods        127
    • Bad pixel maps  129
    • The drizzle algorithm       129
21. Pre-processing in PixInsight
    • WBPP or manual processing?       131
    • Before WBPP: Using CosmeticCorrection 131
    • Using WBPP: Loading and viewing files   132
    • WBPP: Parameters for bias, flats, and darks              134
    • WBPP: Parameters for lights          134
    • WBPP’s Calibration Panel                 136
    • WBPP’s Post-Calibration Panel    137
    • Presets  137
    • Running WBPP  138
    • Manual pre-processing in PixInsight          138
22. Pre-processing in AstroPixelProcessor
    1. APP’s User Interface          142
    2. The files panel    142
    3. The image viewer panel                     143
    4. The pre-processing panel: Steps 1–6          144
    5. The TOOLS panel                 148
23. Pre-processing in DeepSkyStacker             150
24. Pre-processing in Affinity Photo    153
25. Diagnosing common image problems
    • Misshapen Stars                   155
    • Diffraction patterns          157
    • Stray light              158
    • Halos     159
    • Flat fielding problems    159
    • Noise     160
26. Principals and tools of post-processing
    • Types of processing tools                 162
    • Selective adjustments     162
    • PixInsight post-processing sequence         164
    • Photoshop/Affinity post-processing sequence      165
27. Masks and PixelMath
    • Masks in PixInsight            166
    • Creating a luminance mask: clip and convolve      167
    • Creating a star mask with StarNet++          167
    • PixelMath              171
    • Using a uniform mask      173
    • Masks in Photoshop and Affinity Photo   173
    • Creating a star mask in Photoshop or Affinity Photo            174
28. Color synthesis
    • Aligning color channel images in PixInsight            176
    • Aligning color channel images in Affinity Photo  176
    • Cropping out calibration artifacts                 177
    • Aligning histograms with LinearFit             177
    • RGB color synthesis in PixInsight                   178
    • RGB color synthesis in Affinity Photo         178
    • RGB color synthesis in Photoshop                 178
    • Narrowband mapped-color images             179
    • Bi-color HOO narrowband color synthesis                  180
    • Creating HaRGB images 181
    • Combining luminance and RGB data in PixInsight                  182
    • Combining luminance and RGB data in Photoshop or Affinity Photo              183
    • Blending RGB star data into a narrowband image                   183
    • Creating a synthetic luminance image      184
    • Combining color channels in AstroPixelProcessor                  184
29. Color calibration
    • PixInsight’s PhotometricColorCalibration process                 185
    • Other calibration methods in PixInsight  186
    • The PreviewAggregator Script     188
    • Color calibration in AstroPixelProcessor 188
30. Correcting gradients
    • Gradient removal in PixInsight    190
    • Gradient removal with AstroPixelProcessor             192
    • Gradient removal in Affinity Photo              193
    • Gradient removal in Photoshop  193
31. Stretching the image
    • What is stretching?            197
    • Understanding the histogram      197
    • How different curves affect the histogram                198
    • Stretching in PixInsight 200
    • Stretching in AstroPixelProcessor                201
    • Stretching in Photoshop and Affinity Photo             203
    • Posterization: the perils of over-stretching               204
    • Stretching’s effect on color             205
32. Noise reduction
    • Visual noise, color, and scale         206
    • Luminance masking for noise reduction 207
    • An introduction to scale-based processing                207
    • MultiscaleMedianTransform         209
    • TGVDenoise         211
    • One-step masking for TGVDenoise and MMT           212
    • ACDNR 213
    • MureDenoise      215
    • Desaturating the background      215
    • Noise reduction in Affinity Photo                  215
    • Noise reduction in Photoshop      216
33. Adjusting color
    • Enhancing color saturation in PixInsight 217
    • Selecting Colors with PixInsight’s ColorMask script               217
    • SCNR      218
    • Enhancing color saturation in Photoshop and Affinity Photo            218
    • Balancing Color in Photoshop and Affinity Photo 220
    • AstroPixelProcessor’s HSL selective color tool       220
    • Narrowband color adjustment in Photoshop          220
    • Correcting magenta stars in PixInsight    220
    • Correcting magenta stars in Photoshop or Affinity Photo 221
34. Contrast enhancement and sharpening
    • Creating contrast with S-curves  222
    • Contrast enhancement with the soft light blend mode       224
    • Local contrast enhancement in PixInsight                 225
    • Unsharp mask    227
    • Affinity Photo’s Clarity filter          229
    • The high pass filter            230
    • Dynamic range compression with HDRMultiscaleTransform             231
    • Deconvolution vs. sharpening     232
    • Deconvolution in PixInsight          233
35. Star reduction and removal
    • Reducing star size               235
    • PixInsight’s MorphologicalTransformation              235
    • The minimum filter in Photoshop and Affinity Photo           238
    • Starless image processing with StarNet++                 238
    • Star reduction and removal in APP               241
    • Star removal in Photoshop             242
    • Reducing bright stars in Photoshop            243
    • Large halo correction in PixInsight              244
    • Large halo correction in Photoshop and Affinity Photo      245
36. Cosmetic repairs
    • Cosmetic repairs in Photoshop and Affinity Photo                 247
    • Cosmetic repairs in PixInsight      248
37. Plate solving
    • Plate solving       249
    • Image annotation               250
38. Mosaics
    • Planning a mosiac              252
    • Mosaics in AstroPixelProcessor   252
    • Mosaics in PixInsight       253
    • PhotometricMosaic           255
39. Image composition
    • Framing the scene              257
    • Color      260
    • Step away from the computer      261
    • Images and reality              261
40. Example: Nebula workflow (starless)
    • Create the color image   262
    • Separate the stars and nebula      263
    • Process the starless image              263
    • Process the stars                   264
    • Recombine the images and apply final tweaks       264
41. Example: LRGB galaxy workflow
    • Process the color image 266
    • Process the luminance image       267
    • Sharpen fine details and enhance contrast                268
    • Noise reduction and finishing touches     269
42. Example: Star cluster workflow      270
43. What are we looking at? [Digital bonus chapter]
    1. Nebulae                  273
    2. Star clusters         274
    3. Galaxies                  275
44. Appendix A: Deriving the stack efficiency equation       276
45. Appendix B: Deep-sky highlights  277
46. Index  280
47. Further reading         283