Imaging From Our Pristine Boston Skies Not

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Imaging From Our Pristine Boston Skies
(Not!) Thursday, September 13, 2007 Neil
Fleming (www.flemingastrophotography.com)
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Why Even Try from Boston!?
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What Types of Imaging Can We Do?

• Planetary and lunar imaging with webcams
• Narrowband Imaging

• Traditional RGB imaging of Deep Sky Objects

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Planetary and Lunar Imaging

• Done with a simple, inexpensive, webcam
• ToUcam Pro II
• 100
• Instead of long-term exposure of a few dozen
  shots, maximum, you take hundreds or thousands of
  frames from your AVI file
• Each shot is no more than 1/10th to 1/33rd of a
  second in duration
• The image stacking software will choose the
  best frames, from moments of better seeing, and
  give you quite a reasonable result

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Sample Results

• A single, raw, frame

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What is RGB?

• RGB stands for Red, Green, and Blue
• This mix of primary colors is what our eyes use
  to interpret color
• All imaging starts with a black and white CCD or
  CMOS sensor
• Your DSLR cameras utilize tiny red/green/blue
  (RGB) filters over the individual pixels, placed
  in a Bayer matrix pattern
• One-shot color CCD cameras utilize that same
  Bayer matrix

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What is RGB? (continued)

• Most CCD imaging is done with a black and white
  camera, and you use color filters to emulate the
  RGB results so you can obtain a color image
• This takes longer than one-shot color, but gives
  you more resolution in the final result

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What Does RGB From Boston Look Like?

• Light pollution typically causes horrible
  gradients from our stacks of 3-8 minute
  exposures

• A little processing in Photoshop helps, but still
  not great results
• Bright objects are better

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But Narrowband is Even Better!

• RGB takes in the full spectrum, with each filter
  letting in about 200 nm of frequencies
• Narrowband filters let through only the tiniest
  wavelength of light, typically 3 to 13 nm
• These filters are manufactured to let in only the
  light associated with emission wavelengths Ha,
  OIII, and SII
• Other wavelengths are blocked, and this includes
  the vast majority of light pollution
• Typically I use 30-minute exposures
• Result clearer and deeper images!

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Typical Narrowband Pass-through

• Doubly oxidized oxygen (OIII) has its main
  emission at 500.7 nm
• Hydrogen-alpha (Ha) emission wavelength is 656.3
  nm
• Sulfur (SII) emits at 672 nm

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What Equipment do you Need for Planetary Work?

• Telescope
• Almost any scope will do
• Mount
• Can be very basic
• Excellent, long-term tracking, is not required
• However, stability is a definite plus
• Webcam, like a ToUcam 80
• An IR cut filter is very beneficial
• Barlows / PowerMates
• Software
• Registax (free)
• Adobe Photoshop (not cheap)

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How About for Deep Sky Imaging?

• Telescope
• Almost any scope will do
• 200
• Sometimes a flattener or reducer is needed
• Mount
• Stability is critical
• Low periodic error is a plus
• Ability to accept autoguiding commands is
  required for best results
• Cost 1,500 and up
• DSLR or CCD Camera
• DSLR
• Canon, Nikon, etc.
• Can be aftermarket-modified for better red and Ha
  response (Hutech)
• 400 and up

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How About for Deep Sky Imaging?

• CCD Camera
• Simple, like the Meade DSI or Orion Starshoot
  series, 129 to 599
• One-shot color or monochrome
• Wide range of other manufactures
• Starlight Express
• SBIG
• FLI
• Apogee
• QSI
• Costs range from less than 1,000 to 13,000
• Additional guide scope guide camera / head
• SBIG is self-guiding, but that has limitations
• An advantage for narrowband work

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How About for Deep Sky Imaging?

• Filter Wheel
• Come in 1.25, 2, and 2 square formats
• Some are closely coupled to the camera itself,
  while others are standalone and can operate
  independently
• Filters
• For RGB imaging L, C, R, G, B, and sometimes a
  LPR or light pollution reduction filter (Hutech
  IDAS)
• For narrowband imaging Ha, OIII, SII are the
  most common
• Astrodon, Baader, Optec, Custom Scientific,
  Astronomik, Barr, etc.

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How About for Deep Sky Imaging?

• Image capture software
• CCDSoft
• MaxIM
• CCDOps
• Astro image processing software
• CCDStack
• MaxIM
• PixInsightLE
• Downstream image processing software
• Photoshop
• Many different plug-ins

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My Equipment Progression

• Started with
• A refractor (Televue NP-127)
• TAK NJP mount, but with no autoguiding
• Meade DSI-C

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My Equipment Progression

• ..and a ToUcam

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My Equipment Progression

• Added a Meade DSI-Pro (monochrome)

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More Meade DSI-Pro Shots
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Added an SBIG ST-2000XM (Mono)
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Then a TAK FSQ-106NSV
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Started Playing with Narrowband/Ha
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Full Narrowband Ha/OIII/SII with STL-6303
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Added Paramount, TOA-150, then TMB 203 F/7
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OK, So How Do You Do This?

• Get set up for some quality imaging time!
• start with an interminable wait for clear skies
• Drag your mount and scope out
• Set up your gear, and do your polar alignment
  (for a GEM)
• Field rotation effects in non-polar aligned
  Alt/Az
• Use MaxIM / CCDSoft to take your images
• RGB/LRGB can be done in a couple of hours
• Narrowband takes at least one night, if not
  longer
• Dont forget your darks and flats

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Huh? What are Darks!?

• CCD chips are neither perfect nor uniform
• Individual pixels can be hot
• Clusters of minor defects
• Potential column defects
• There is dark current (thermal) noise in your
  chip
• Thermal noise is associated with the build up of
  signal on the CCD chip, even when no light is
  present, due to heat
• The amount of thermal noise drops off quickly
  with lower temperatures
• By cooling a CCD chip, the dark current can be
  reduced to an acceptable level
• Good astronomical CCDs have cooling systems that
  can lower chip temperatures by 35 degrees C or
  more
• To mitigate this thermal noise, we take darks
  at the same CCD temperature and duration that we
  used for our light frames

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What on Earth are Flats!?

• We need to deal with dust on our filters, CCD
  chip, and telescope optics
• Also, optic systems are hotter in the middle of
  the frame than they are at the edges
• This is particularly apparent for fast, short
  focal length scopes like the FSQ
• You take images of a uniform surface/sky, so as
  to capture these flaws
• Flat lightbox
• Dusk or dawn flats
• These are divided into the lights during
  calibration

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Processing Combine in CCDStack

• Load the individual subexposures (subs)
• Calibrate them (apply your darks and flats)
• Do some bloom rejection, if necessary
• Register or align the individual images
• Apply normalization to appropriately weight the
  contribution of the individual subs
• Perform advanced noise rejection for outliers and
  cosmic ray hits, airplane trails, etc.

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Processing Combine in CCDStack

• Stack or combine the subs into a channel master
• Repeat for each filter or color
• Further noise reduction
• Deconvolution, if desired
• Save as a scaled TIF (mono/narrowband)
• For RGB, you probably want to do the color
  combine in CCDStack it has nice color
  adjustment tools

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Processing Adobe Photoshop

• For RGB, the color combine was already done in
  CCDStack
• For narrowband, I recommend processing individual
  channels for maximum quality before the color
  combine. The OIII/SII is weak relative to the
  Ha. For each channel
• Noise reduction (Either with PS tools, or
  NeatImage)
• Contrast adjustments via adjustment layers like
  levels or curves
• Do a channel merge to make your color image

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Narrowband Palettes
Red (Ha) / Green (OIII) / Blue (SII) is
Canada-France-Hawaii Telescope (CFHT) palette
Red (SII) / Green (Ha) / Blue (OIII) is the
famous Hubble palette
Red (Ha) / Green (sG) / Blue (OIII) is the
Synthetic Green palette
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Processing Adobe Photoshop

• Color balancing
• RGB is usually good to go
• Narrowband
• The Ha often overpowers the OIII and SII, so some
  balancing is required
• Channel Mixer
• Selective Color adjustments
• Levels (use lightly)
• Curves
• Gradient removal
• Russ Cromans Gradient XTerminator
• Noise reduction, if not already done

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Processing Adobe Photoshop

• Contrast enhancements
• Curves
• Noel Carbonis Local Contrast Enhancement
  Photoshop Action
• Shadow/Highlight adjustment
• Sharpening
• Convert to jpg and upload to web site

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Time for a Demo?