Astrophotography with a DSLR Tom Nicolaides Carriere, MS M4

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS
M42 53x30s, ISO1600
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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• List of acronyms and obscure terms
• DSLR Digital Single Lens Reflex
• CCD Charge Coupled Device
• T adapter A coupling ring that allows standard
  accessories (such as nosepieces, field flatteners
  and coma correctors) to be attached to a DSLR
  camera
• RA Right Ascension
• Dec Declination
• Light Frame A single image of some object
• Dark Frame A single image of dark (with the
  scope cover on), used to compensate for noise and
  Amp Glow
• Flat Frame A single image of an evenly
  illuminated field, used to compensate for an
  unevenly illuminated light frame
• Amp Glow The appearance of a glow in or along
  one side of any frame caused by the heating
  effects of the sensors amplifier

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• DSLR vs CCD camera
• The DSLR can be used for other things besides
  Astronomy
• In general a DSLR has a much larger imaging area
  than a dedicated CCD
• A DSLR costs a LOT less
• DSLR has much higher noise than a cooled CCD
  camera
• DSLR has more limited color range than a CCD
  camera (in general), and less dynamic range (14
  bit for the typical DSLR and 16 bit for a CCD
  camera)
• Whats needed for DSLR Astrophotography?
• A telescope, of course to start, keep the FL
  relatively short say 400 to 1000mm The Orion
  ED80 is one of the most popular. Meades Schmidt
  Newtonians are popular
• A good mount LXD75, Vixen GP class at a
  minimum. The Losmandy G11 seems to be one of the
  main workhorses of astrophotography. The Orion
  Atlas is coming on strong.
• Focusing aid
• DSLRFocus
• Stiletto
• Through the viewfinder Not recommended
• Hartman Mask
• Methods to control the shutter
• Timed Remote
• DSLRFocus
• DSLRShutter
• A manual release and stopwatch

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• What else is needed?
• Software for processing At least one of the
  following, with many considering Photoshop an
  essential addition.
• ImagesPlus
• IRIS (free)
• PixInsight (free)
• MaximDL
• Photoshop
• Eventually you will want to guide. This will
  take a 2nd camera a webcam, DSI, Guiding
  software such as PHD. Reason? Even the best
  mounts cant stay on target much more than 2 or 3
  minutes. However, excellent photos can be taken
  unguided if you keep the exposures short (less
  than 60s) and take care to get a good polar
  alignment
• Now, you dont REALLY need a computer and
  separate imager to guide. You can do it manually
  with a guidescope and reticule eyepiece. Place a
  guidestar in the crosshairs and make small
  adjustments to RA and Dec to keep it centered.

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• So how do you do it?
• Mounting the camera to the focuser is
  accomplished using a T adapter and nosepiece
  (usually 2 inches)
• Try focusing through the viewfinder on a distant
  object during daylight. This will get you in the
  right ballpark
• Now its nighttime and time to focus for real.
• If an aid such as the Stiletto is used, the
  method is fairly foolproof. Attach the Stiletto
  to the camera adapter (The stiletto is made for
  specific cameras). Point to a bright star.
  Adjust your focuser until the diffraction lines
  disappear. Lock down your focuser. Remove the
  Stiletto. Re-mount your camera. Youre done.
• If you use something like DSLRFocus, use it to
  take a sample image. Select a star. Adjust
  focus until DSLRFocus tells you its right. This
  takes some back and forth between the computer
  and focuser. Its taken me as long as 15 or 20
  minutes to get it right in this way.
• One can also achieve focus using a Hartman mask.
  This is done by making a front cover to the
  telescope with 2 or more holes in it. Point the
  scope at a bright star and adjust focus until the
  star images converge.
• Time to start acquiring images

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• Acquiring images (sub-frames, light frames,
  darks, flats)
• Always set your camera to RAW mode. This
  prevents the camera from messing with your
  picture no stretching, etc.
• Try to get at least 30 light frames regardless of
  your exposure time. This will make processing
  and noise reduction easier. And in general
  youll get a better final product
• Acquire at least 5 dark frames at the same
  setting as your light frame. The dark frame will
  help in subtracting out camera noise from your
  light frames. Dont forget to put your scope
  cover on or it wont be dark!
• Acquire several flat frames. This is a photo of
  an evenly illuminated, featureless object. It is
  used to correct for an unevenly illuminated field
  of view. Virtually all scopes/camera combinations
  have vignetting. A flat frame will correct for
  this and other things like dust motes in your
  optical path.
• A flat may be taken at daytime by pointing the
  scope to an area of blue sky
• A flat may be taken at night by covering the
  scope front with a white T shirt and illuminating
  it with a flashlight.
• Some take a dark frame to apply to their flat.
  This would be taken at the same ISO and shutter
  speed. I generally dont do this as a flat
  exposure is usually so short that noise isnt a
  problem.
• You now have your data set. Time for processing!

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• Heres a typical single light frame, unstretched.
  Nothing spectacular.

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• Youll need software to convert your RAW files
  into something your processing software can work
  with. I use ImagesPlus for this and most other
  processing things. There are many others, some
  of which are free most notable are IRIS,
  PixInsight, DeepSky Stacker and Gimp.
• Here are the processing steps I go through
• I convert the entire data set (lights, darks and
  flats) into lossless, compressed FITS format.
• I make a master dark by averaging and combining
  my dark frames
• I make a master flat by averaging, combining and
  de-saturating the color
• Next step is calibration of the light frames.
  This is where the master dark and master flat are
  applied. With ImagesPlus, one tells the software
  the name of the master dark and flat. It then
  applies the masters to each light frame and makes
  a calibrated set of light frames.
• Next is alignment. Select the same star in each
  calibrated light frame. Tell your software to
  align. It makes a new set of calibrated, aligned
  light frames
• Next is combining. There are several methods for
  combining frames Simple average, sigma-clipped
  average, addition and others. The method used
  depends often on the quality of your subframes
• At this point youll have a partially complete
  photo. It wont look like much. Some additional
  things need be done.

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• After your have your combined image, youll need
  to do some things to it that your camera in RAW
  mode doesnt do.
• Using ImagesPlus, I apply Digital Development.
  This feature examines the levels of the photo and
  adjusts them such that intensity range spans the
  range of the photograph.
• The left is the combined image (sigma clipped
  average) of IC443 (43 subframes, 240s each) the
  right is after Digital Development.

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• After this I go to Photoshop. I adjust levels
  again and use Curves to expand the photo.
  Sometimes I use an Unsharp Mask to bring out
  details. Heres the final result of the
  supernova remnant IC443

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• Where to start
• I suggest selecting a fairly large, bright
  object, such as M42 or M8. Other good first
  attempts are open clusters such as M35, 36, 37
  and 38
• Use a relatively short exposures 30 to 60
  seconds. Experiment with speed (ISO setting),
  but ISO800 should get good initial results
• Try to get between 30 and 60 light frames
• Make sure to take a set of darks and flats
• Process as described here and dont be afraid to
  experiment!

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• Other considerations
• The standard Canon DSLRs, and the Nikons too, do
  not have much sensitivity to the Hydrogen Alpha
  spectral signature (deep red). However, this is
  not a limitation of the sensor, but an artifact
  created by the introduction of an aggressive IR
  filter.
• It is possible to modify a DSLR to take out
  and/or replace this filter with one more friendly
  to the light of emission nebulae.
• There are companies or people who will do this
  for you, most notably Hutech.
• My new camera is a Canon 350D (the Digital Rebel
  XT) modified by Hutech. To see the difference,
  look at the two following photos.

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Astrophotography with a DSLRTom Nicolaides
Carriere, MS
The image on the left is a composite of nine 6
minute images and took a LOT of sweat in post
processing to tease out the detail. The image
on the right is a composite of seventeen 4 minute
exposures (same OTA) And was very easy to
process. Thats the difference between the
modified and unmodified cameras,
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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• What else can be done?
• Heres an image of M1, the crab nebula taken by
  Mike Broussard of Louisiana and the same image of
  M1 taken by Hubble.

The Crab Nebula - 2X Drizzle Processing, 21x150
sec _at_ ISO 1600, Meade SN-8, MPCC, IDAS-LPS,
Hutech Canon 350XT
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Astrophotography with a DSLRTom Nicolaides
Carriere, MS

• Additional Resources
• The Cloudy Nights DSLR Forum http//www.cloudynig
  hts.com/ubbthreads/postlist.php/Cat/0/Board/DSLR
• My own humble web site http//www.first-light.or
  g
• The Astromart forums http//www.astromart.com
• Hutech http//sciencecenter.net/hutech/index.htm
  
• Mike Unsolds ImagesPlus http//www.mlunsold.com/
  
• DSLRFocus http//www.dslrfocus.com/
• Hap Griffins cables and connectors
  http//www.hapg.org/astrocables.htm
• Shoestring Astronomy http//www.store.shoestringa
  stronomy.com/
• A Guide to Astrophotography with DSLR Cameras
  http//www.astropix.com/GADC/HELP.HTM