This document provides an overview of the basic concepts, equipment, planning, and techniques needed for deep sky astrophotography. It discusses using inexpensive equipment like cell phones and discusses free and low-cost software options. Key steps covered include focusing, taking calibration frames, capturing long-exposure images, stacking images to reduce noise, and processing the stacked image through techniques like non-linear stretching to enhance details. Guiding and tracking mounts are also discussed for taking exposures longer than a few minutes.

1. GHAAS Imagers
March 2021
By
Mark Casazza

2. Orion from Mountain Top
 This 213 6-second shots @ 1600 f/3.5 28mm

3. Agenda
 Basic concepts
 Minimum equipment
 Planning
 Capturing
 Processing
 Stacking
 Developing
 Printing

5. Basic Concepts
 Taking a picture of the dark
 High ISO (gain) – adds noise
 Long exposures – adds noise
 Very dim objects – signal strength ~ noise level
 This is a battle against noise
 Lots of pictures – coax the signal from the noise
 Cool the electronics – minimize the noise
 Calibration frames – subtract the noise
 Need uncompressed data
 Don’t have a DSLR or astro-camera, don’t fret

6. Why Raw and not JPG
 Compression
 Small deviations are lost in compression
 This is your data being destroyed!
 14 bits vs. 8 bits
 16384 shades vs. 256 shades
 Your data: 800 to 1600 vs. 12 to 25 shades
 64x more data!

7. Three Types of Astrophotography
 Easy – Star Trails, Moon
 Moderate – Meteor showers
 Challenging –
 Deep Sky
○ This will be my focus; I will explain the others as I go
 Planetary
○ We will cover this at another time. It is arguably the most difficult type

9. This doesn’t have to be expensive
 The $3.95 budget
 Modern iPhone or Android cell phone – 3.95
○ http://www.camerafv5.com/
 ProCamera for the iPhone – $8.99
○ https://www.procamera-app.com/en/
 Deep Sky Stacker – Free
 Gimp 2.10 – Free
 Computer to process
○ Okay, so you need a computer
 Stable place and way to set the phone/camera

10. FV-5 Cell Shot
 Camera: LG-H815
 Exposure: 30 sec
 F/1.8
 ISO-2700
 http://a.disquscdn.com/uploads/mediaembed/images/
2914/3911/original.jpg

11. Other non-DSLR options
 Canon Point and shoot cameras
 CHDK $0.00
 http://chdk.wikia.com/wiki/CHDK
 Android Phone
 Manual Camera $4.99
 FV-5 $3.95
 A Better Camera $0.99
 iPhone
 Pro Camera $8.99
 Pro Cam $7.99

12. Optimal Minimal Equipment
 Rock solid tripod
 Consider sandbags to hold it still
 Prime lens vs. zoom lens
 The less glass the better, each surface is an opportunity for light loss and
reflections. Prime.
 Focal ratio
 The faster the lens the better, but…
○ Some lens have distortions when wide open
○ Astrophotography will expose them
 Remote or timed trigger
 Even better, lock the shutter open
 Bahtinov mask (focusing tool)

14. Planning – What to Shoot
 What is your field of view?
 Sensor size (Canon T1i is 22.3mm X 14.9mm)
 Focal Length of lens (35mm)
 FOV = sensor/focal length * 57.3
○ 22.3/35*57.3=13.6 X 14.9/35*57.3=24.4
 Look for objects that fill up at least 40% of the field
○ Moon is 0.5 (would require 380mm to use 40%)
 What is up tonight?
 Summer favorite is the Milky Way
 Winter favorite is Orion
 The Moon is harder than you think

15. Don’t Forget to Check the Weather
 http://clearoutside.com/forecast

17. ClearDarkSky.com
 Get email alerts from
 ClearSkyAlarmClock.com

19. Basic Steps
 Acclimate the camera to the environment
 Leave camera outside 30 minutes prior to use
 Focus – This is a lot harder than you think!!!
 The longer your focal length the harder to focus
 Set exposure
 Frame
 Shoot, take lots of shots. Over 100. Really!
 If it is cold outside put the camera in a zip lock back before
you bring it in.

20. Focus – Bahtinov Mask Usage
 Place mask over lens
 Take picture
 Adjust focus
 Repeat until all lines meet in
center
Search for “Bahtinov Mask dslr” on Amazon

21. Exposure Time & ISO
 Your camera is stationary the sky is not!
 “Sky Speed” varies
 https://www.lonelyspeck.com/advanced-astrophotography-shutter-
time-calculator/
 35MM lens on a T1i at
○ Declination 0: 8 seconds
○ Declination 70: 17 seconds
 For star trails ignore this time
 You want the maximum ISO before insane noise
 For the T1i this is 1600
 Newer cameras can go higher

22. What is Declination
 Declination is the number of degrees the center of the shot
is from the celestial equator.
 Polaris is at 90
 Simple enough?
 Not sure, use 0

23. Star Trails - Calculating exposure
 Carefully remove the Bahtinov mask
 Take a sample shot
 Inspect histogram
 You want the left side to be away from the left wall, but not too much
○ Left peak is the sky’s brightness
 If you have another peak on the right avoid it hitting the far right
○ Right peak is any large foreground object

24. Frame the Object
 Carefully remove the Bahtinov mask
 Remember, the sky is moving
 Objects move around the North Star
 For most directions this is East to West
 West of the North Star (south to north)
 East of the North Star (north to south)
 North of the North Star (west to east)
 Set up so your target moves through the frame

25. Frame the Object
 Remember the sky is moving
 Objects move around the North Star
 Set up so your target moves through the frame
N
W
E
S
W
E

26. Take Pictures – Lots of
Pictures
 Take as many pictures as you can
 30 to 50 exposures is where you start to have limited returns
 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024
○ You half the noise with every doubling
 20 second exposures
 35mm lens has is 34 by 24
 It takes 96 minutes for the sky to rotate 24
 30 minutes @ 20 seconds = 90 shots
 Big or empty SD card and strong battery help
 Optional AC adapter or 12V converter is helpful

27. They Don’t Look Great at First

28. But wait, there is an image there!

29. Darks Frames – Take at Least 30
 If it gets cloudy or your object sets, & you can keep your
equipment out take darks
 Darks are equal length exposures at the same temperature
with the lens cap on
 You can also build a dark library
 This captures the “exposure noise”
 These are important but optional

30. Bias Frames – Take at Least
30
 You can take these any time
 Take the shortest possible exposure with the lens cap on
 This captures the “read noise” of the chip
 These are helpful and optional

31. Flat Frames – Take at Least
30
 Without touching the focus
 Take a picture of an evenly illuminated field
 A grey card can work here
 Try to get a similar histogram to your images
 Need varies depending on vignetting of the image from
“nice to have” to essential
 Generally, these are essential

32. Pre-Processing Math
 Pre-processing is applying darks, flats, and bias to the
individual images before stacking
 Light - bias - (dark - bias)  (flat - bias) = Frame
 If you skip this step and just stack lights, 

34. Essential Stacking
 The goal of stacking is to take every frame, line up the stars
and combine them into a single shot. This will:
 Drive out noise
 Create more “bits” of dynamic range
 DSLR’s start with 14 bits, after ~10 sub-frames you can have a true
32-bit floating point intensity value.
 Inspect all frames for bad ones
 Combine all the lights, darks, bias, and flats
 Each program has a different process, learn yours, try the
options
 For star trails you just stack without aligning on stars

35. Stacking Software
https://nightskypix.com/astrophotography-stacking-software/
 Sequator – Free – Windows
 Deep Sky Stacker – Free – Windows
 Autostakkert! – Free – Windows
 Lynkeos – Free – Mac OS X
 SiriL – Free – Windows, Mac OS X, Linux
 More if you want a commercial product

37. What is Non-Linear
Stretching?
 90% of your data occupies 10% or less of the
“data space”
 The goal is to get this to cover 75% or more
of the “data space” without blowing out the
bright areas
 Each image needs different treatment
Orig Targ
0 0
5 60
10 110
15 150
20 180
25 195
50 210
75 215
100 220
125 225
150 230
175 235
200 240
225 245
250 250
0
50
100
150
200
250
0 50 100 150 200 250

38. Digital Development & More
 This is an astro-photo specific process to bring out dynamic
range into a visible space
 You can do this yourself with levels and curves
 Or buy special software $$ Star Tools, PixInsight, Nebulosity
 There are many other tricks!
○ If you are interested, watch this video
Requires PhotoShop, maybe Lightroom or Gimp 2.10
○ http://www.astronomersdoitinthedark.com/dslr_llrgb_tutorial.php

39. Other Special Issues
 Gradients & Vignetting
 Amp glow
 Lens/Scope vignetting
 Sky glow (even and uneven)
 Noise removal
 The whole process is a battle against noise
 Exaggerated colors / saturation
 Real colors are not as saturated as many like
 Color alignment
 Each color focuses slightly differently
 Highlight the nebula, surpass the stars

40. Commercial Software under $100
 Backyard EOS or Backyard
Nikon – $50
 Image acquisition for DSLRs
 Star Tools – 60 AUD ($45)
 Digital development
 Color correction
 Noise removal
 Many other processing tricks
 Nebulosity – $95
 Image acquisition - CCD
 Stacking
 Digital development
 Luminar AI - $99
 Image processing
 Astro Photography Tool (APT) -
$22
 Image acquisition
 Computer focusing!
 Plate solving via PS2 or Astro Tortilla
(Both Free)

41. So, You Have a Tracking Mount!
 Alt-Az mounts
 Allow longer exposures, but not multiple minutes
 Equatorial mounts
 Anything from an EQ-1 to a Paramount
 Polar alignment is essential for good performance
 Cable management is essential for your sanity
 Long focal length = Very difficult
 Short focal length = Relatively easy
 Start short with experience go long

42. Cable Management

43. Accurate Polar Alignment
 PoleMaster – Neat piece of unnecessary equipment
 Assumes your mount’s case in plumb
 PHD2 offers a drift align process that is
 Easy (once you understand it)
 Accurate (to arc-seconds of accuracy)
 https://openphdguiding.org/PHD2_Drift_Alignment.pdf
 Steps
 Rough align on Polaris
 Perform Drift Align in PHD2
 Stop when you are satisfied, don’t go crazy!
○ I generally settle for 5 arc minutes or less error

44. Long exposures
 Most good equatorial mounts can support a 3-minute
exposure without guiding depending on your focal length
 Your mileage will vary
 Guiding is essential for longer exposures
 Short focal length 10mm to 400mm
○ Optional, but will improve images
 Mid range focal length 400mm to 2000mm
○ Essential beyond 2 to 4 minutes – Guide scope
 Long focal length 2000mm+
○ Essential period – Consider a pick off mirror

45. What is Guiding?
 While your main camera takes a long exposure
 A guide camera is taking short pictures
 A computer is interpreting the picture
 The computer is sending commands to the mount to correct for any
tracking errors
 PHD2 is the primary guiding software
 Despite its name “Press Here Dummy” it is rather complex to
properly configure.
 At longer focal lengths a guide scope has too much flexure;
you need to use a pick off mirror

46. With and Without Guiding