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INTRODUCTION TO ASTRO-
PHOTOGRAPHY
Stillwater StargazersMarch 2016
ByMark Casazza
Agenda Basic concepts Cost from $5 to $50,000+ Planning Capturing Processing
StackingDevelopingPrinting
Basic Concepts
Basic Concepts Taking a picture of the dark
High ISO (gain) – adds noiseLong exposures – adds noiseVery dim objects – signal strength ~ noise level
This is a battle against noiseLots of pictures – coax the signal from the noiseCool the electronics – minimize the noiseCalibration frames – subtract the noise
Why Raw and not JPG Compression
Small deviations are lost in compressionThis is your data being destroyed!
14 bits vs. 8 bits16384 shades vs. 256 shadesYour data: 800 to 1600 vs. 12 to 25 shades64x more data!
Equipment Cost
This doesn’t have to be expensive The $3.95 budget
Modern Android 5 (Lollipop) cell phone○ http://www.camerafv5.com/pages/manual-cam
era-controls-table.phpFV-5 software – $3.95Deep Sky Stacker – FreeComputer to process – Okay so you need
one of these too.
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
But you can go nuts
http://downthewormhole.blogspot.com/2011/05/das-planewave.html
What Serious Investment Buys
What was that? Planewave 12.5” CDK: $12,500 Apogee U16: $17,500 Paramount Me: $15,000 Optec 3” focuser: $900 Filter wheel & filters: $1,000 Pick off mirror Guide scope Motorized focus
My Rig Mount: Orion EQ-G Primary Scope: Explore Scientific ES ED 127 Primary Camera: Full Spectrum Canon Ti1 Guide Scope: Orion “Short Tube 80” Guide Camera: Meade DSI Pro Focuser: Rigel n-step with USB and temp Image Capture: Backyard EOS
Test driving Sequence Generator Pro Computer: eBay Dell Laptop
My Rig
My Dark Sky Setup
Session Planning
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=0.9Look 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?
Software Tools Spreadsheet with NGC/IC
My creation - I can provide Sky Tools 3 ($100 or $125) TonightsSky.com (shameless plug)
Sky Tools 3
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=sky&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
NWS Hourly Forecast
ClearOutside.com
ClearOutside.com
ClearDarkSky.com Get email alerts from
ClearSkyAlarmClock.com
AccuWeather.com They provide an Astronomy summary
Image Capture / Acquisition
Basic Steps Normal Scope Setup For equatorial mounts
Rough Polar Align with polar scopeDrift align – This is essential for longer exposures
Sync Scope to ComputerI use plate solving
Focus on bright starBahitnov Mask
Frame Target Fine Focus Start guiding (if you are auto guiding)
Bahtinov Mask Usage Place mask over
primary Take picture Adjust focus Repeat until all lines
meet in center
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
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 DitherDithering is jogging the scope a small bit between
shotsCauses hot pixels to move around relative to the starsDither!
They Don’t Look Great at First
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
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 cameraDLSR camera adapter
Filter wheel (if using a monochrome camera) Specialty Camera Reducer/Corrector/Field Flattener Laptop
Flats – take at least 30 Before you move the camera, you need
to take flats Flats are pictures of an evenly
illuminated sceneDawn skyT-shirtLight box
This captures any vignetting and dust in your system
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”
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
Image Processing - Stacking
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 noiseCreate more “bits” of dynamic rangeDSLR’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 upSome 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
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
Software Deep Sky Stacker – Free Nebulosity - $95 Images Plus - $240 CCD Stack - $200 Pix Insight - $230 Euros ($250)
Image Processing - Stretching
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 Targ0 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
Digital Development This is an astro-photo specific process to
bring out dynamic range into a visible space Software
Nebulosity – $95Images Plus - $20Pix Insight - $250Star Tools – 60 AUD ($45)CCD Stack - $200
Other special issues Gradients & Vignetting
Amp glowLens/Scope vignettingSky glow (even and uneven)
NoiseThe whole process is a battle against noise
Exaggerated colors / saturationReal 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 alignmentEach color focuses slightly differently
Simulators Black Body
http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html
How eye sees colorhttp://phet.colorado.edu/sims/html/color-visi
on/latest/color-vision_en.html
General Purpose tools Photoshop / Lightroom
Expensive!Very powerfulFull 16 bit supportLimited 32 bit support
GimpFreeSimilar features to PhotoshopFull 8 bit supportLimited 16 and 32 bit support
More options on the Mac
My Generic Workflow Pre-process in Nebulosity Initial stretch and enhance in Star Tools
StretchCropBinHRD, Contrast, etc.ColorDe-noise
Final tweaking in PhotoshopFinal stretchFinal color saturation
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
Future topic Image Acquisition
Camera selectionTelescope/lens selectionGuidingFrame, focus & exposureCapture software
Future topic Basics of Image processing
Calibration frames (darks, flats, & bias)StretchingColor correctionColor saturationSoftware suggestionsLive demo using tools costing under $50
Future topic Free and Inexpensive AP software
Deep Sky StackerAstro Photo Tool (free version)Sequence Generator (free version)GimpCDCBackyard EOS
Future topic Photoshop tricks & tips
Works with Gimp tooLevels & CurvesLayers & MasksScreen Mask Invert to pull out dim detailBlock Method for more color saturationLab color by channel curve for color
saturation