Getting Started in CCD Imaging

1
Getting Started in CCD Imaging

• An Overview by Alan Chen
• Member of
• CFAS Central Florida Astronomical Society
• Chiefland Astronomy Club

2
Agenda

• Hardware
• The scope
• Optics
• Mount
• About Periodic Error
• The camera
• Choices
• MX7C - my first camera
• SXV-H9C - my second camera - a loaner
• Software choices for imaging/processing
• Basic imaging steps
• Some Images

3
Hardware The Scope

• The choice of telescope is as important as the
  choice of camera
• Important factors The optics
• Choose a scope with the best optics you can
  afford
• Investigate on-line the pros and cons (i.e. Yahoo
  Groups)
• How color free is the scope (i.e. achro vs. APO)
• How flat is the field - this is important if the
  cameras chip is large (i.e. gt10mm or you intend
  to use film)
• RC and refractors are best, but expensive
• Fast Newts and focal reduced SCTs have more
  curvature
• Amount tolerable depends on cameras chip size to
  be used
• Dedicated field flatteners will help, but adds
  glass and cost
• How large and heavy is the scope - easy to setup?

4
Hardware The Scope

• Important factors The mount
• The mount should be rated to handle at least 1.3x
  the maximum amount of weight you intend to carry
• Allows a degree of stability margin
• Total includes the scope, guide scope, scope
  brackets, dovetails, camera(s), and accessories
  (camera adapters, dew heaters, etc.) as part of
  the total weight
• Most popular scopes are packaged with mounts
• Meade LX and Celestron Nexstar series - the most
  popular first choice for starting out
• Fork mounts do not allow significant weight to be
  added (only about 10 to 12lbs. with careful
  balancing required)
• Periodic error is higher, but can be guided out
  if smooth

5
Hardware The Scope

• Important factors The mount
• GEMS (German Equatorial Mount)
• The mount of choice for higher end imaging,
  although at generally higher costs
• Celestron has the new CGE series - not much data
  out yet, but promises to be a step up from the
  fork mounts at a competitive price to forks
• Aftermarket GEMs provide an alternative
• Paramount ME (10000), Astro-Physics (4000 to
  8000), Takahashi (3000 up), and Losmandy (2000
  to 6000) are good examples of higher end mounts
• The Vixen GP-DX is probably the best low cost
  mount on the used market
• Advantages are higher total weight capacity
  (except for the Vixen GP-DX) and improved
  Periodic Error (PE)

6
Hardware The Scope

• Examples of fork and GEM mounts

7
Hardware The Scope

• Periodic error or PE - what is this and why is it
  important
• PE is a measure of the fundamental error present
  in the worm/gear assembly during tracking
• Caused by machining errors, out of roundness in
  either worm or main gear, particles/dirt, bearing
  tolerances, etc.
• Errors are typically reported in /- arc-seconds
• Typical mass produced mounts have errors that are
  on the order of /-20 arc-sec or higher
• High-end GEMs are typically specd at better than
  /-5 arc-sec
• PE is easily measurable with ccd camera and
  tracking software (deviation from ideal tracking)

8
Hardware The Scope

• Examples of Periodic error in arc-seconds
• PE for the Synta EQ6 (/-35) and Vixen Atlux
  (/-10)

9
Hardware The Scope

• Examples of Periodic error
• Losmandy G11 (/-12) and Takahashi NJP (/-5)

10
Hardware The Scope

• Examples of Periodic error
• Losmandy Titan - right plot (measured with the
  MX7C camera at approximately /-3.5)

11
Hardware The Scope

• Periodic error
• Mounts with the smoother PE plots from point to
  point and the smallest total errors will guide
  better
• Smoother lines means that there are no large
  error jumps to guide out (no fast transients)
• Smaller total error means fewer and smaller
  corrections during guiding
• This does not discount mass produced scopes for
  imaging
• For mounts with higher errors, use of shorter
  focal length scopes or SCTs with focal reducers
  will provide excellent guiding results and very
  nice images
• Most of my images with the LX200 were taken at
  f/4

12
Hardware The Scope

• In summary
• Choose a scope/mount combination that has good
  optics and comes with a sturdy mount
• An alternative is to buy the optical tube by
  itself and an aftermarket mount if this fits your
  budget
• PE is an important factor if the scope is to be
  used for imaging
• High end mounts have low PE to allow higher
  resolution imaging (i.e. at f/10 with a 12
  scope)
• Mass market scopes can do very well at imaging,
  but may require focal reducers (SCTs) or shorter
  focal length refractors to account for increased
  PE

13
Hardware The Camera

• Choosing the camera
• There are many options to begin imaging with
• Digital camera - easiest way to start
• Research the web for choices
• Nice results achieved with Olympus, Nikon and
  others
• SLRs coming into popularity (like the Canon D60)
  but expensive
• Webcam - excellent for planets (check QCUIAG
  website)
• True CCD version (not CMOS based)
• Philips Toucam Pro, Vesta Pro, Older
  Logitech/Connectix
• Video camera - i.e. StellaCam-EX
• Deepsky capable with integrating software
• True CCD camera for astro-imaging
• Utilizes the most sensitive chips for deepsky
  imaging

14
Hardware The Camera

• What makes a deepsky capable CCD camera?
• The chips employed are the most sensitive
  available
• Sensitivities range from about 50 to 90
  efficient
• For example 50 efficiency occurs when an
  electron is generated for every 2 photons hitting
  that pixel
• There are other techniques to improve
  sensitivity, including the use larger pixels,
  incorporating micro-lenses on top of the pixel
  (Kodak and Sony both use this technique) and back
  illumination, where the photons hit the back of a
  very thin chip to avoid being blocked by the
  front side circuitry (Site chips)
• The cameras employ active cooling of the chip
• Peltier coolers (like those in portable coolers)
  are used
• Cools the ccd chip to approximately 30C below
  ambient
• Primary purpose is to reduce the thermal noise of
  the chip

15
Hardware The Camera

• What makes a deepsky capable CCD camera?
• The newer cameras are all 16bit for the highest
  quality images (65k shades of gray)
• Resolutions are lower but catching up to digital
  SLR (most common are 0.4 to 1.6 megapixels)
• Unlike typical cameras, there are no built-in
  lenses or other user adjustments to the hardware
• Requires software to extract the image from the
  camera
• Requires software to control the camera
  including
• Exposure time
• Taking a sequence of exposures
• Guiding or tracking (with a guide camera)
• Cooling (if software controlled like the SBIG
  line)

16
Hardware The Camera

• True CCD camera
• Several major CCD camera vendors
• Apogee - high end cameras (i.e. more expensive)
• Utilizes SITE chips - very sensitive as a result
  of back illumination
• FLI - high end cameras (i.e. more expensive)
• Also utilizes back illuminated chips, but has
  more inexpensive offerings as well from Kodak
• SAC - very inexpensive to start with
• SAC8 the best choice, but requires parallel and
  USB ports
• Older models use vid cam technology for summed
  exposures
• Lacks strong software support, but still
  relatively new

17
Hardware The Camera

• True CCD camera
• Several major CCD camera vendors
• SBIG - probably the largest and most recognizable
• Wide range of cameras based on Kodak chips
• Excellent standalone autoguiders (STV, ST4)
• Starlight Express - excellent values for ccd
  cameras
• Wide range of cameras based on Sony chips
• Kits for Cookbook or Audine cameras are available
  for those who are handy
• All are good choices and span prices ranges for
  all levels of imager (approximately 1000 to
  10,000)

18
Hardware The Camera

• Starlight Express - my choice!
• MX7C - why was this a good first choice for me?
• An excellent first camera
• Good chip size for starters and more advanced
  imagers
• Relatively simple to operate, especially for
  color images
• Affordable by CCD standards
• 750x582 resolution tops in its price range
• Small and compact - only 2 dia
• Light weight
• Balance kit not necessary for the LX200
• Approximately the weight of a good 2 eyepiece -
  only 200 grams
• Primary SBIG equivalent considered at the time
  ST-7E

19
Hardware The Camera

• Starlight Express
• MX7C - why was this a good choice for me (cont.)?
• One shot camera - color matrix filters - CMY
• Synthesizes RGB from the filtered signals
• Much less overall imaging time involved for color
• Color filter wheel not required
• Probably not as accurate a color balance as RGB
  imaging
• Color synthesis routines much improved recently
  in Astroart
• Self-guiding capability with Star2000 interface
• Uses the same chip for imaging and guiding (every
  other interlaced row)
• Sensitivity reduced by 50 as a result
• Full frame usable to locate a suitable guidestar
  (convenient)!
• Simple software interface to self-guide

20
Hardware The Camera

• Starlight Express
• MX7C - why was this a good first choice for me
  (cont.)?
• USB output
• 6.47mmx4.83mm chip
• 752x580 resolution
• Small size (50mmx100mm)
• Light weight - 200 g
• MX716 - mono version

21
Hardware The Camera

• Starlight Express
• Todays alternate choices I would consider
• MX716 - a sensitive and low cost mono camera -
  the best value on the market today (1395)
• SXV-H9 - first megapixel camera (2795)
• Extremely low noise/dark current
• Dark frame not used by many SXV imagers
• SXV-H9C - good sensitivity, especially for color
  (2795)
• Uses an RGBG (Bayer Matrix) - not CMYG
• Color resolution will be much improved
• Extremely low noise/dark current - dark frames
  not required
• Primary SBIG equivalent to consider ST2000XM
• Slightly larger chip and slightly higher cost
  (3495)
• Includes built-in guide chip - very convenient

22
Hardware The Camera

• Starlight Express
• SXV-H9C - The camera Im currently using
• On loan from Adirondack Video and Astronomy for
  me to try out

23
Hardware The Camera

• Comparing the 2 one-shot cameras

• MX7C
• USB 1.1 output
• 6.47mmx4.83mm chip
• CMYG filter matrix - G used for luminance
• 752x580 resolution
• 8.6umx8.3um pixels
• Small camera size (50mmx100mm)
• Light weight - 200 g
• MX716 - mono version

• SXV-H9C (mega-pixel)
• USB 2.0 output
• 9.00mmx6.70mm chip
• RGBG filter matrix - G used for luminance
• 1392x1040 resolution
• 6.45umx6.45um pixels
• Small camera size (63mmx100mm)
• Light weight - 400g
• SXV-H9 mono version

24
Hardware The Camera

• The SXV-H9C has improved color resolution
• Compare M27 (single 4 or 5 min. frame) - MX7C
  (top), SXV-H9C (bottom) - only RGB, no Luminance

25
Hardware The Camera

• The SXV-H9C has improved color resolution
• Close-up of the red frames
• New extraction technique in the works to improve
  color resolution further

26
Hardware The Camera

• The SXV-H9C uses an improved interface
• Simple hookup (shown w/optional guide camera)
• Only 2 connections - 1 to computer and 1 to AC
  power

27
Hardware The Camera

• Use a rigid coupling of camera to scope if
  possible to minimize flexing
• Left to right
• Camera
• T-thread spacers
• T-thread to SCT adapter
• Focal reducer
• SCT to 2 adapter

28
Hardware The Camera

• Alternate method of coupling camera to scope not
  as rigid using set screw arrangement
• Left to right
• Camera
• Camera to 1.25 adapter
• 1.25 visual back
• Focal reducer
• SCT to 2 adapter

29
Hardware Matching Scope and Camera

• General guidelines
• Sampling definitions
• Good seeing (i.e. lt2 arc-sec) can tolerate higher
  sampling rates
• Sampling rate (arc-sec/pixel) 206 x (pixel
  size)/(focal length)
• Pixel size is dependent on the camera
• FL can be varied by focal reducers and barlow
  lenses
• Rule of thumb scope and camera should provide a
  typical sampling rate of between 1 and 3
  arc-sec/pixel
• 12LX200 _at_ f/3.3 1.7 arc-sec/pixel (good
  match!)
• Ratesgt2 is under-sampling and rateslt2 is
  over-sampling
• High resolution imagers use 1/3 to 1/4 the seeing
  value to maximize resolution (i.e. down to 0.5
  arc-sec/pixel!)
• My advice - dont worry about sampling
• Excellent results can be achieved from 0.3 to gt7
  arc-sec/pixel

30
Software Choices

• Software comes in several flavors
• Bundled with camera
• Generally not as full functioned, but enough to
  get started
• All in one handles both image capture and
  processing (2 main ones listed)
• Astroart by MSB (179) - excellent value
• Maxim CCD/DL (365) - higher end package
• Processing only
• Maxim DL (285)
• Post processing (tweaks)
• Photoshop
• Corel Photo

31
Basic Imaging Steps Taking the Image

• Imaging process
• Setup scope, camera, laptop and align
• No hot plugging - turn everything on after full
  setup

32
Basic Imaging Steps Taking the Image

• Choose and locate first object
• For LX200, slew to it using HPP (nice ccd
  feature)
• For other setups, manually locate or goto
• Focus on a nearby star when convenient
• Will get focus close before slewing to object
• Take a quick 10 sec shot
• Focus on a brighter star
• Setup guider (if applicable)

33
Basic Imaging Steps Taking the Image

• Set the exposure time (240s in this case)

• Note the guide window and active tracking at the
  top right
• Image started with 240 seconds set - bar at
  bottom left indicates exposure progress
• The image will pop up on screen when completed

34
Basic Imaging Steps Processing

• Use the processing software to complete the image
• Typical processing includes
• Stacking and aligning images if more than one
  image is taken
• Multiple images taken for increased total
  exposure
• Improves signal to noise
• Shorter images prevents saturation from light
  pollution
• Sharpening to improve object definition
• Median filtering to remove hot pixels (bright
  dots)
• Contrast and stretching to bring out fainter
  details

35
Basic Imaging Steps Processing

• Color processing - LRGB combined result
• This should approximate the final result

36
Basic Imaging Steps Processing

• Color processing
• Use color balance and saturation commands to
  further enhance the image
• Flipped image for orientation
• Can tweak further in Photoshop and Corel
  Photopaint

37
Some Images M16 - The Eagle Nebula
38
Some Images M27 - The Dumbell Nebula
39
Some Images M22
40
Some Images M22
41
Some Images NGC5907
42
Some Images NGC6992 - The Veil
43
Some Images Mars
44
Thanks for watching!Check out
http//www.heavenlyview.comfor more info on ccd
imaging and the latest images (in full size - the
ones used here were resized and cropped to fit
causing some resolution loss)