The Deep-sky Imaging Primer

The second edition of The Deep-sky Imaging Primer is a substantial update to the first edition, with revised and expanded text and over 325 illustrations. Printed in full color, it covers everything you need to know to capture stunning images of deep-sky objects with a DSLR or CCD camera:

  • The fundamental concepts of imaging and their impact on the final image
  • How to pick a telescope and camera
  • How to get set up and take the images
  • Where and when to find the best objects in the night sky
  • How to process images using Adobe Photoshop® and PixInsight®
  • Start-to-finish examples of image processing

Complete coverage of PixInsight® has been added, with workflows for both PixInsight and Photoshop®.  There are also two new start-to-finish processing examples.  The early chapters have been revised, with clearer explanations of important topics like noise and resolution. And a new appendix provides details of the best imaging targets for northern hemisphere imagers.  Overall, it’s a bigger, more readable book, with a lot more content.

Click here or the image below to order the book from Amazon. 

2e Cover v4 - front only (small)

Like the first edition, the book is structured in three sections:

  • Understanding Images explains how electronic sensors work and introduces the critical concepts of signal and noise.
  • Acquiring Images describes how to use telescopes, cameras, and computers to capture deep-sky images.
  • Processing Images is the longest section, covering everything you need to know to turn raw data from the camera into a deep-sky masterpiece. In addition to Adobe Photoshop, it now includes full coverage of PixInsight, which is fast becoming the main image processing tool for many imagers.

I’m happy to answer any questions at

Table of Contents

Understanding Images

1     Electronic sensors

The challenges of deep-sky imaging 8

How electronic sensors work                8

Well capacity and bit depth 9

The trade-off between dynamic range and gain           10

The importance of bit depth 11

Response curves and raw files             12

Creating color images             13

Sensor architecture 14

A CMOS revolution? 15

2     Signal and Noise

A little statistics and quantum physics             16

Signal and noise at the pixel level      17

Shot Noise   18

An example of shot noise      20

A dimmer example   22

Skyglow       23

Thermal signal, hot pixels, and dark frames   24

Read noise and quantization noise   25

Variation in two-dimensions                26

Adding signals and noise      27

Acquiring Images

3     Mounts and Alignment

Meridian flip               31

Polar alignment        32

Drift alignment         33

Tracking error            34

Balancing a mount   34

4     Cameras

DSLRs            35

Dedicated astronomical cameras       35

Sensor size and pixel size      36

Connecting a camera to a telescope  37

5     Telescopes and optics

Fundamental optical parameters       38

Telescopes for visual vs. imaging use               38

Optical aberrations  39

The Strehl Ratio        40

Refractors    40

Telephoto lenses      42

Reflectors and compound telescopes               43

Telescope quality     45

6     Image scale: matching sensor and optics

Resolution and seeing            46

Sampling     47

The three constraints on resolution  48

Field of view               49

Equipment recommendations             50

Focal reducers and field flatteners     51

The ‘f-ratio myth’ debate       52

7     Choosing objects to image

Getting a sense of scale          53

The deep-sky catalogs            53

Object types and the seasons              54

A survey of object sizes          57

Giant Objects (2° or greater) 57

Really Big Objects (1–2°)        58

Objects from 30–60′ 58

Objects from 15–30′ 58

Objects from 5–15′   58

Objects from 1–5′     58

Objects smaller than 1′           58

8     Focusing, guiding, and setting up

Focusing      59

Achieving critical focus          59

Autoguiding fundamentals  60

Connecting computer to mount          62

Software and settings            63

Reducing setup time               64

Dovetails, rings, and other mount accessories              65

Power supplies          65

Dew prevention        66

USB cables and hubs               66

9     Filters and narrowband imaging

Filters for imaging   67

Narrowband filters  67

Light pollution filters             69

DSLR filters and modification              70

10     Taking the exposures

Controlling the camera          71

Choosing exposure duration and gain             71

Planning for a night of imaging          73

An image capture workflow  73

Dark frames                74

Flat frames  75

Bias frames  76

Dithering light frames            76

11     Atmospheric effects

Light pollution          77

Target altitude          78

Local turbulence       79

12     Diagnosing problems and improving image quality

Wind or tracking errors          80

Diffraction patterns 81

Flat fields     81

Focus            82

Halos             82

Tips for better images             83

Processing Images

13     Color in digital images

Raw data and image file formats         85

Visual response to color         85

Color management and color spaces 87

LAB color     88

The HSL/HSV/HSB color model            88

White balance and color temperature              88

Deep-sky color accuracy        89

Color calibration with G2V stars         89

14     Calibration and stacking

Calibration exposures            90

Throwing out problem shots                92

Stacking parameters               93

Calibration and stacking with DeepSkyStacker             94

The drizzle algorithm              97

Calibration and stacking with PixInsight        98

Creating a master bias in PixInsight  98

Creating the master dark and flat in PixInsight            99

Integrating light frames in PixInsight              101

Combining data from multiple nights               105

A PixInsight pre-processing cheat sheet          105

Using the BatchPreProcessing script 107

Diagnosing defects in calibration output        107

15     Principals and tools of post-processing

PixInsight, Photoshop, or…?               108

Types of processing tools and a basic workflow            109

Selective adjustments            110

16     Processing images in PixInsight

The PixInsight user interface               111

Working with images in PixInsight    112

Working with processes in PixInsight               115

Image and process containers             115

Saving the workspace as a project file              116

ScreenTransferFunction        116

A PixInsight post-processing workflow           117

17     Processing images in Photoshop

Layers           119

Layer blending modes            120

Creating a composite layer   120

Selections and feathering     120

A Photoshop post-processing workflow          121

18     Using masks

Masks in PixInsight 122

Creating a luminance mask with the
RangeSelection process         123

Creating a star mask with StarMask   123

PixelMath    127

Using a uniform mask to moderate an effect 128

Masks in Photoshop 129

Creating a star mask in Photoshop    129

19     Color synthesis and gradient removal

Aligning separate color channel images          131

Cropping out calibration artifacts      131

Aligning histograms with LinearFit   132

RGB color synthesis in PixInsight       132

RGB color synthesis in Photoshop     132

Narrowband mapped-color images   133

Correcting gradients               133

Gradient removal in PixInsight           134

Gradient removal in Photoshop         135

Color calibration in PixInsight            138

The PreviewAggregator Script            139

PixInsight’s PhotometricColorCalibration process      140

Combining luminance and RGB data in PixInsight       141

Combining luminance and RGB data in Photoshop     142

Creating a synthetic luminance image             142

20     Stretching: reallocating the dynamic range

What is stretching?  144

Understanding the histogram             144

How different curves affect the histogram      146

Nonlinear transformation in PixInsight           148

Nonlinear transformation in Photoshop         149

Keeping the background neutral in Photoshop            150

Posterization: the perils of over-stretching    150

The effect of stretching on color         151

21     Noise reduction

Visual noise, color, and scale                152

Noise reduction in PixInsight              153

Masking for noise reduction 153

An introduction to scale-based processing    153

MultiscaleMedianTransform 155

ACDNR          157

TGVDenoise                158

SCNR             159

Noise reduction in Photoshop             159

22     Adjusting color

Enhancing color saturation in PixInsight        160

Enhancing color saturation in Photoshop      160

Narrowband color adjustments in PixInsight 162

Narrowband color adjustments in Photoshop              165

Mapping color in Photoshop with clipping layer masks             165

Correcting star color in narrowband images  166

Blending RGB star data into a narrowband image        167

Balancing Color in Photoshop             168

23     Contrast enhancement, sharpening, and deconvolution

Creating contrast with S-curves          169

Object-background separation curves             169

Intra-object contrast curves 170

Local contrast enhancement in PixInsight      172

Dynamic range compression with HDRMultiscaleTransform    175

Local contrast enhancement in Photoshop with blend modes 175

Unsharp mask (Photoshop and PixInsight)    176

Photoshop’s HDR Toning tool             178

Photoshop’s high pass filter 179

Deconvolution vs. sharpening            180

Deconvolution in PixInsight 180

24     Star reduction and removal

Reducing background star size           183

PixInsight’s MorphologicalTransformation tool          184

The minimum filter in Photoshop      186

Reducing the brightest stars 187

Star removal and separation in PixInsight      187

Star removal in Photoshop   190

25     Cosmetic repairs

Cosmetic repairs in Photoshop           193

Correcting elongated stars   193

Cosmetic adjustments in PixInsight  194

26     Image composition

Framing the scene    195

Orientation 196

Color             198

Step away from the computer             198

Images and reality   198

27     Plate solving and mosaics

Plate solving and image annotation 199

Mosaics        200

28     A DSLR processing example    203

29     A CCD processing example      210

30     A Photoshop processing example      216

Exercise Answers      221

Moonlight Tables     224

Deep-sky Highlights           228

Index         233

  1. Pranjal Verma
    June 4, 2013 at 2:15 am

    How to buy this book in India. From Amazon, shipping charges are more than the cost of the book.

    • June 4, 2013 at 5:29 pm

      Hi Pranjal –

      I’ll see if I can find a more cost effective way to get a copy to you. Send me a note at with your shipping address, and I’ll send you a quote.


  2. Rod Hutson
    September 29, 2013 at 4:15 pm

    Hi Charles, I live in Canada and discovered that doesn’t carry your book, which I thought was odd… anyway, is there anywhere in Canada that can source it for me (bricks-and-mortar or online)? – Rod

    • September 29, 2013 at 5:01 pm

      Hi Rod –

      Sorry for the book not being listed on I can have a copy sent to you (media mail) for US$32. That takes 1-3 weeks. (Priority Mail is ridiculously expensive, but available for $47.) If you are interested, email me at deepskyprimer*AT* You may also check’s rates to ship a copy to you in Canada, as they may actually be able to ship it cheaper than I can.

      Thanks for your interest!

  3. November 10, 2013 at 6:38 am

    Hi Charles,

    I’d like to thank you for your book! I’am french, I was trying to find a book about deep sky imaging but in french there are only 2 or 3 books that are dealing with astrophotography in general. Then I find your book on Amazon by chance. I looked inside and found it very good, with simple explanations… I bought it and I’m not disappointed! I had read the first part of your book and I find the answers to many questions… Thanks again! I’am going to read the next parts 🙂

    • November 10, 2013 at 8:37 am

      Thank you for your kind words about the book! I am happy to hear that the explanations are clear to you. I hope you enjoy reading the rest of it, and please send me a note if you have any thoughts or suggestions.

      Best wishes,

  4. December 16, 2013 at 12:09 am

    You produced a wonderfully readable and information-rich book! I bought a copy about 4 months ago, and find I’m constantly referencing it for one thing or another. Yours is the first imaging book I’ve purchased, and I would eagerly recommend it to others. Excellent work!

    • December 18, 2013 at 7:49 am

      Thank you very much, Sorin. I am glad that you are enjoying the book. And nice pics of Comet ISON on your blog, by the way!


  5. December 25, 2013 at 6:30 am

    This was the x-mas gift from my wife. So far, it looks VERY good and informative .

    • December 25, 2013 at 8:46 am

      Merry Christmas! I hope you enjoy the book, and feel free to shoot me an email if you have any questions or suggestions.

      Best wishes,

  6. Angelo Pierfanti
    August 17, 2014 at 3:58 pm

    I think the book is great, however the font used is way too small. It is nice looking, but I have to make a real effort to read it. I would have much preferred a thicker book, but easy to read, after all books are meant to be read, not to be looked at. That is too bad, as the book deserves all the praises, and I do hope that a future edition considers this point of view. Thank you.

    • August 17, 2014 at 4:53 pm

      Thank you for your helpful comment, Angelo. I am working on the second edition, and I have indeed increased the font size by one point. I’d rather have a thicker book too, but the book’s cost is based on the number of pages, so increasing the font size can increase the final price of the book. To balance the increased font size, I’m planning to increase the size of the book itself from 8×10 inches to 8.5×11 inches.

      Best wishes,

      • Angelo Pierfanti
        August 25, 2014 at 6:20 am

        Hello Charlie,

        Thank you for your reply. I understand your concerns and am glad to read there will be a second edition with an increased font size. Do you know when it will be out? Thank you.

        Best regards,

      • August 25, 2014 at 9:05 pm

        Hi Angelo –

        My goal is to have the second edition ready for NEAF in April.


  7. January 17, 2015 at 3:43 pm

    Have you considered releasing the book as an e-book? It’s great having a paper copy to read from cover to cover, but I find e-books much better for a quick reference. An e-book can go with me wherever I have my iPad. Eithe e-pub or pdf would be great.

    • January 18, 2015 at 10:13 am

      Hi Brooks –

      I am looking into it for the second edition, as I’ve gotten a lot of requests. How would you feel about Apple iBooks vs. epub?

      • mbrooksclark
        January 18, 2015 at 10:32 am

        Apple iBook is even better from my perspective.

      • November 16, 2016 at 4:35 pm

        Hi Charlie, would like to buy both your Primer and The Astrophotography Sky Atlas. But I’m just interested in ebooks, for several reasons. I travel a lot, like to look back on stuff I have read, and then save shipping duration, cost – and environment. Unless truly forced – a principle. Many great hi-res tablets these days. No idea why you would choose iBook platform lock-in. Kindle is at least everywhere. ePub is great, can even accept (Adobe) DRM. If you do, please let me know, and don’t forget adaption to be within the readable! (this guy, like plenty of others, forgot to check:

      • November 19, 2016 at 10:51 am

        Thank you for the feedback. Now that the ePub and Kindle formats seem to be maturing, I will consider offering the second edition as an eBook. I’ve had several similar requests, and I completely understand the convenience of eBooks. I read most of my magazines now on the iPad. There are some challenges with the eBook formats that still make me hesitant due to the nature of my books: they are full-color with high resolution images. Neither book would be appropriate for monochromatic eReaders, as a lot of information is communicated with color in the figures, and one of the chapters is specifically about color. I fear the atlas is possibly too high resolution to work on an eReader. If I had a way to prevent those with monochrome devices from purchasing the books, I would be more comfortable. I don’t want anyone to be disappointed after downloading an expensive eBook!

        I still have a long way to go with the second edition though, so perhaps things will be different by the time I’m ready to publish it. Or perhaps I need to create a specific version for tablets that is designed for the format. I’ll investigate my options, and appreciate any additional thoughts you have.


  8. Greg
    March 12, 2015 at 4:30 pm

    I am hesitant to buy this first edition if the second edition is being released soon. What are the plans for the second edition, still looking for ab April release date?

    • March 12, 2015 at 4:52 pm

      Sorry, work commitments have delayed my ability to finish the second edition. I do not expect to have it ready until later in the year now.


  9. deepskyov
    September 6, 2015 at 9:47 pm

    Hi, Any news about the second edition? I can’t wait 🙂

    • September 6, 2015 at 10:58 pm

      I’ve re-written sections 1 and 2 already, and I’m re-writing section 3 with a much greater focus on PixInsight this time. I have another book coming out next month (an astrophotography atlas), so work on that has delayed the second edition of this book. Thanks for your interest! When the second edition comes out will mostly depend on my work schedule, but I don’t think it will be ready before the end of this year.


  10. November 11, 2015 at 1:57 am

    I bought this about 18 months ago as a newbie. It’s one of the best you can buy on the subject. Covers most of the significant concepts in a relatively simple langauage that one can understand. Especially stuff like full well capacity, the coverage of the field of view and then processing tips as well. Well written with clean colour images. I still use it whenever I need to brush up. I bought several books before but this is the stand out for DSLR especially.


  11. Michael Ogle
    January 25, 2016 at 2:29 am

    I have the First Edition. I was working thru the exercises and came to Exercise 1.3 on page 33. The answer on p.185-186 confused me. How did you get 18.3 e- per second? From Ex 1.2, the thermal noise was 1.68e- per second at 20 deg C.

    • January 26, 2016 at 9:48 pm

      You are correct, this is an error in the book that carries over an old version of the question. The answer to 1.2 should read:
      “An exposure of 20 minutes at 40 degrees Celsius would produce 20 min x 60 sec x 1.68 e- per second = ~2014 electrons. Dark current would fill 2014 / 25500 = ~8% of the full well capacity. The brightest capturable level would be 25500 – 2014 = 23486. The noise from the dark current is SQRT(2014) = ~45 electrons. The read noise is given in the problem as 10 electrons, thus maximum theoretical dynamic range is 23486 / (45 + 10) = 428, or 53 dB.

      For the same exposure at -15C, following a similar set of calculations, the dynamic range would be 25468 / 15.6 = 1629, or 64 dB.

      (Note that we are simplifying our calculation of total noise here by not using the proper summing in quadrature method, as that is not covered until the following chapter, but this simplification does not have a meaningful impact on the results.)”

  12. toggle
    March 6, 2016 at 1:06 am

    Hi! I see there’s mention of a second edition of this book being prepared last year. Will that be released soon? I’d like to buy it.

    • March 6, 2016 at 8:11 am

      I took a year off from writing the second edition to create The Astrophotography Sky Atlas. Now I’m working on the second edition again, but it’s still a long way from done. Sorry for the delay. It can be hard to squeeze in the time to write with a full-time job and family!

  13. Larry Field
    March 26, 2016 at 12:59 am

    Hi from New Zealand. I wonder if your Astrophotography Star Atlas includes the Southern Hemisphere for all of us below the equator? I assume that you have probably spent most of your focus on only the Northern Hemisphere. thanks.

    • March 26, 2016 at 7:58 am

      Hi Larry – The atlas covers the entire Southern Hemisphere in the same detail as the Northern Hemisphere. With so many great objects visible from “down” there, I couldn’t leave out the southern skies!


  14. Bjorn Crewe
    April 19, 2017 at 5:00 pm

    Hi, I´m here to bug you, good Sir, for a digital version of your work. In my search for just that I see illegal downloadable copies in pdf-format out there. I simply refuse to go that way, it would not be fair to all that work you´ve put into your books.

    SO many people have a full colour tablet these days, I really think your work would reach more people that way. Pictures could be enlarged for potentially better viewing than on paper.

    E-books tend to come cheaper as well, no postage, no paper, instant delivery, has a lot of benefits. Please concider some sort of comercially available digital version of your work soon.

    For my personal interest, the Deep-Sky Imaging Primer is my first wish. I´m rather impatient when I see something I need for my hobbies. I´ll probably acquire the printed version none the less, while I wait for my wish to come true (around Christmas? 😉 ).

    Kind regards and hopes for clear skies
    Bjorn, Denmark

    • April 20, 2017 at 4:03 am

      Hi Bjorn – I appreciate your thoughtful note. As the e-reader market evolves (and I get feedback from potential readers like you), I am reconsidering my publication options. I still need to do some research on pricing structure, file formats (Kindle vs. ePub vs. iBooks), and resolution. All of my efforts right now are still on finishing the upcoming book, but once I’m done with that, I can see about releasing a digital version of The Deep Sky Imaging Primer.


  15. Bjorn
    April 21, 2017 at 9:51 am

    Thanks, Charlie. And best of luck with your current work.
    I will order the hard copy asap. Can’t wait…

    To promote the digital version you could stress the practicality of having it along in dark conditions (if the book should find it’s use in real-time-next-to-scope situations, idk.), some ebook-apps have night lighting, so one doesn’t spoil night vision.

    I use both Blue Fire and iBooks, the former comes in both iOS and Android. Some inspiration:

    Clear skies (and clear types)

  16. Stan Burman
    October 28, 2017 at 12:27 am

    The Second Edition is available on Amazon today. Fantastic!

  17. April 8, 2018 at 11:34 pm

    Hi Charlie, minor copy error you’re probably already aware of. On page 171, figure 230 covers up the text. It’s not a critical error as the intent is clear in the image, but I wanted to make you aware of it. Stu

  18. April 21, 2018 at 5:34 am

    Thank you Stu. The next printing will correct this error as well as a few typos.

  19. Stephen
    October 21, 2018 at 1:53 am

    I was wondering if your book shows information on filter wheels? I have two stellarvue refractors (80 & 105 triplets). What are the advantages of electronics over manual? Or is there any? I haven’t found anything that talks about filter wheels. Or what size filters are best 1-1/4” or 2”).
    Thanks in advance.

    • October 21, 2018 at 7:42 pm

      Hi Stephen – Electronic filter wheels have enormous benefits. Mainly, it’s because you can set them to be controlled from your computer, allowing you to automate your imaging session with software like AstroPhotographyTool or Sequence Generator Pro. Otherwise, you’d have to sit by your scope all night and turn the filter wheel manually. Also, manual filter wheels won’t have the same accuracy in turning to the exact same spot, which is required for flat fielding.

      As for filter sizes, there isn’t a “best”–it depends on the sensor size, how close the filters are to it, and the focal ratio. For most APS-sized sensors, 1.25″ are okay for focal ratios slower than f/4. SBIG cameras of this size don’t put the filter as close the sensor, they usually use 36 mm filters. Larger sensors require 2″ filters.

      Hope that helps!

  20. January 6, 2019 at 7:56 am

    Hello Charles, would it be possible to promote the information and image of the book in the next issue of the amateur astrophotography magazine please?

    Looking forward to your reply

    • January 6, 2019 at 10:00 am

      Hi Steve – Yes, that would be great! Please shoot me an email at and let me know if you need a high-res image or anything like that. I also have a new book coming out next week that you might be interested in.


  21. Stuart Boyle
    May 6, 2019 at 3:14 pm

    Charles, I am enjoying your book. However, to get the most out of it you kind of need to be in front of the computer working through the examples you give. It would really be helpful if you could provide the images you use in your book to demonstrate PixInsight for download so that we could replicate your results as we work through the examples



    • May 6, 2019 at 9:02 pm

      Hi Stuart – I’m so glad to hear you are enjoying the book! The files used in the examples were several gigabytes in size, and I’m not sure I have them all at this point. Is there is a specific example you’d like to try? I can see if I can find the original data and send your way.


  1. February 23, 2013 at 11:05 am
  2. September 20, 2014 at 9:28 pm
  3. October 22, 2014 at 3:38 pm

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