4. 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
5. 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. This doesn’t have to be
expensive
The $3.95 budget
Modern Android 5 (Lollipop) cell phone
○ http://www.camerafv5.com/pages/manual-
camera-controls-table.php
FV-5 software – $3.95
Deep Sky Stacker – Free
Computer to process – Okay so you need
one of these too.
16. Planning – What to shoot
What is your field of view?
Sensor size (Canon T1i is 22.3mm X 14.9mm)
Focal Length of lens or scope (952mm)
FOV = sensor/focal length * 57.3
○ 22.3/952*57.3=1.3 X 14.9/952*57.3=0.9
Look for objects that fill up at least 40% of the field
What is up tonight?
How late do you plan to stay up?
Where are you?
17. Software Tools
Spreadsheet with NGC/IC
My creation - I can provide
Sky Tools 3 ($100 or $125)
TonightsSky.com (shameless plug)
19. Other Planning to Consider
Object surface brightness and your SQM
Weather
http://forecast.weather.gov/MapClick.php?w0=t&w1=td&w2=wc&w3=sfcwind&w3u=1&w4=sk
y&w5=pop&w6=rh&w7=rain&w8=thunder&w9=snow&w10=fzg&w11=sleet&w12=fog&w13u=
0&w16u=1&w17u=1&AheadHour=48&FcstType=graphical&textField1=40.437&textField2=-
84.3797&site=all&unit=0&dd=&bw=&BackDay.x=72&BackDay.y=11&BackDay=0
http://clearoutside.com/forecast/40.44/-84.38?view=current
http://www.cleardarksky.com/c/NwBrmnOHkey.html?1
http://www.accuweather.com/en/us/coudersport-pa/16915/astronomy-weather/335322
Local Obstructions & Lights
Guide star
For advanced folks who use a pick off mirror
○ Sky X helps with this
○ CDC to a much lesser extent
26. Basic Steps
Normal Scope Setup
For equatorial mounts
Rough Polar Align with polar scope
Drift align – This is essential for longer exposures
Sync Scope to Computer
I use plate solving
Focus on bright star
Bahitnov Mask
Frame Target
Fine Focus
Start guiding (if you are auto guiding)
27. Bahtinov Mask Usage
Place mask over
primary
Take picture
Adjust focus
Repeat until all lines
meet in center
28. Calculating exposure
Take a sample shot
Inspect histogram
You want the left side to be away from the left
wall, but not too much
If you have a tool to do spot histograms check
galaxy & nebula core for over exposure
○ Backyard EOS has this
You may have to shoot several exposures (M42)
Check focus & remove Bahitnov mask
29. Take 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
To Dither or not to Dither
Dithering is jogging the scope a small bit between shots
Causes hot pixels to move around relative to the stars
Dither!
31. Software
Came with the camera – Free
Backyard EOS - $50
Astro Photography Tool - ~$21 **
Sequence Generator pro - $100 **
Images Plus - $240 **
Nebulosity - $95
CCD Auto Pilot - $100 to $300 **
** Provides auto focus capabilities
32. Special Hardware
Bahitnov mask
Guide scope and camera
Or pick off mirror and camera
Guide-able mount
Computer control
ST4 port (with ST4 guide camera)
(Modified) DSLR camera or CCD camera
DLSR camera adapter
Filter wheel (if using a monochrome camera)
Specialty Camera
Reducer/Corrector/Field Flattener
Laptop
33. Flats – take at least 30
Before you move the camera, you need
to take flats
Flats are pictures of an evenly
illuminated scene
Dawn sky
T-shirt
Light box
This captures any vignetting and dust in
your system
34. Darks – take at least 30
If it gets cloudy or your object sets and
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”
35. 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
37. 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 exceptional frames that will
mess things up
Some programs auto score shots for focus
○ Nebulosity
○ FITS Image Grader (by Main Sequence)
Combine all the lights, darks, bias, and flat frames
Each program has a different process, learn yours,
try the options
38. Theory
Bias represents the read noise
Subtract from the flat or light frame
Darks represent the exposure noise
Subtract from the light frame
Flats show vingetting and dust motes
Apply to light frame
41. 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
25% or more of the “data
space” without blowing out the
bright areas
Each image needs different
treatment
Orig Targ
0 0
10 10
15 23
20 36
25 49
30 62
35 75
40 80
50 87
60 93
70 99
80 105
90 110
125 130
150 150
250 250
42. Digital Development
This is an astro-photo specific process to
bring out dynamic range into a visible space
Software
Nebulosity – $95
Images Plus - $20
Pix Insight - $250
Star Tools – 60 AUD ($45)
CCD Stack - $200
43. Other special issues
Gradients & Vignetting
Amp glow
Lens/Scope vignetting
Sky glow (even and uneven)
Noise
The whole process is a battle against noise
Exaggerated colors / saturation
Real colors are not as saturated as we like to see in
our pictures
○ Stars broadcast every wave length (blackbody)
○ Nebula radiate specific frequencies or reflect blackbody
Color alignment
Each color focuses slightly differently
44. Simulators
Black Body
http://phet.colorado.edu/sims/blackbody-
spectrum/blackbody-spectrum_en.html
How eye sees color
http://phet.colorado.edu/sims/html/color-
vision/latest/color-vision_en.html
45. General Purpose tools
Photoshop / Lightroom
Expensive!
Very powerful
Full 16 bit support
Limited 32 bit support
Gimp
Free
Similar features to Photoshop
Full 8 bit support
Limited 16 and 32 bit support
More options on the Mac
46. My Generic Workflow
Pre-process in Nebulosity
Initial stretch and enhance in Star Tools
Stretch
Crop
Bin
HRD, Contrast, etc.
Color
De-noise
Final tweaking in Photoshop
Final stretch
Final color saturation
47. Software to consider
Sky Tools 3 - ($100 or $125)
Backyard EOS - $50
Astro Photography Tool - ~$21
Sequence Generator pro - $100
Images Plus - $240
Nebulosity - $95
CCD Auto Pilot - $100 to $300
Deep Sky Stacker – Free
CCD Stack - $200
Pix Insight - $230 Euros ($250)
Nebulosity – $95
Star Tools – 60 AUD ($45)
Photoshop or Lightroom – Expensive!
Gimp - Free
49. Future topic
Basics of Image processing
Calibration frames (darks, flats, & bias)
Stretching
Color correction
Color saturation
Software suggestions
Live demo using tools costing under $50
50. Future topic
Free and Inexpensive AP software
Deep Sky Stacker
Astro Photo Tool (free version)
Sequence Generator (free version)
Gimp
CDC
Backyard EOS
51. Future topic
Photoshop tricks & tips
Works with Gimp too
Levels & Curves
Layers & Masks
Screen Mask Invert to pull out dim detail
Block Method for more color saturation
Lab color by channel curve for color
saturation
Hinweis der Redaktion
Let the battle against noise begin! Each frame is full of noise, so much noise you could never use it.
Never, never, never shoot JPGs and expect good results. Even with a cell phone invest in a program like FV-5 that captures “Raw” data
Assuming you have a modern cell phone and reasonable laptop, you can get some nice pictures for no investment
You can also process Hubble images to get good at processing without even owning a telescope.
With a modern cell phone and software that avoids compressing the image you can do real astro-photography
Or you can invest a small fortune
Probably spent $50,000 on that rig
Other things to consider if you are using filters is the filter to use as the objects climbs. Shoot Red, Green, then Blue as an object rises.
I use my spreadsheet and Sky Tools
Polar alignment is criticle
Focus is critical and changes with temperature. Recheck focus during the night
Focus is critical and changes with temperature. Recheck focus during the night