Astrophotography - Methods

Night sky portraits

Night sky portraits are a great way to get started in astrophotography. You can photograph your favorite constelations, even relatively bright comets, and some of the brighter deep sky objects. For example one of my first nights taking some constelation pictures I decided to take one of Cygnus. I was delighted when part of the North America nebula (NGC 700) showed up.
  • Camera capable of taking long exposures
    Look for a B or Bulb setting. An old SLR camera is perfect for this.
  • Lense with a medium to wide field focal length. 55mm or lower works well for this.
  • Trypod - My trypod is the cheepest one Wal-Mart had and works well for my uses
  • Cable Shutter Release - Highly recommended to control the shutter without shaking the camera. Get a good one, I had one from National Camera break on the 2nd use. You can get a surprizingly good quality one from Orion telescopes and Binoculars for about $20 US

  • Set camera up on tripod
  • Set the camera exposure to its B or Bulb setting - this makes the camera open the shutter for as long as you hold the button or shutter release cable
  • Set the exposure (/f ratio) to one of its lowest numbers. f/5.6 is a good one
  • Focus camera at infinity
  • Aim at the constelation or part of the sky you want to photograph
  • Start the exposure by pressing and holding the shutter release button. 30 seconds will capture stars as well as the brighter deep sky objects.
  • Stop the exposure by depressing the button.

    These are very general guidelines. Experiment! You'll be suprized what you can get doing this

    Piggy Back - Mounting a camera on top of an equitorial telescope to track the stars movement through the sky

    By mounting a camera on top of a telescope (Piggy Backing) you can achive longer exposures by compensating for the Earth's rotation and following the stars through the sky. This also allows higher focal lengths than the Night Sky Portrait method

  • A telescope with an equitorial mount
  • A clock drive for the equitorial mount
  • Camera capable of taking long exposures (Look for a B or Bulb setting)
  • Cable Shutter Release for the camera capable of locking for hands free operation. You will need your hands for guiding.
  • A camera adaptor for your telescope that works like a standard tripod (1/4" bolt)
    1/4" Camera Adaptor
  • A high magnification eyepiece (8mm or smaller FL).
    An illuminated reticle eyepiece is highly recomended, and virtually required if you're using a long (100mm or greater) focal length lense on the camera. This is an eyepiece with illuminated crosshairs.

  • Align: Polar align the telescope
  • Focus: With the camera focused at infinity, or focus on a brigther star (not too bright).
  • Set the camera's shutter time to B or Bulb
  • Aim: This can be very dificult, it helps to calculate the field of view of your lense compare on a star chart what you will see when the object is centered.
  • Start the clock drive
  • Find a guide star through the telescope and center it in your eyepiece, make sure it's tracking well by watching it for a minute or so
  • Start the exposure by locking down the shutter release
  • Guide: make occasional corrections, for example move the guide star to the center of the eyepiece every 30 seconds or so.
  • When you think you've exposed long enough (or a car is comming and is about to shine right into your lense!) stop the exposure by unlocking the shutter release.

    Afocal coupling - Photography through the telescope

    Afocal coupling is the same as holding a camera with lense up to the eyepiece of the telescope. For best results you will want to use a mount. Shown in the picture is Orion's steadypix camera mount connected to my Sony Mavica digital camera through the 1/4" tripod mount and clamped on to a 10mm eyepiece.
    With afocal coupling it is better to use a digital camera or a web cam than film.
  • Telescope - preferably with a clock drive
  • Camera - preferably digital or web cam
  • Camera Mount - highly recommended, you can also use a tripod and get okay results
  • Remote shutter release - highly recommended, preferably one with an interval timer
    Procedure - taking the pictures
  • If your camera has manual focus capability, set it to manual and focus on infinity
  • If your camera lets you change the exposure, set it to the lowest number (widest aperture)
  • If your camera lets you set the ISO, set it to the highest setting in order to achive the shortest exposure time.
  • Make sure your lense is as close to your eyepiece as you can get within reason, taking care not to scratch your lense or filters.
  • If you are using a camera mount which couples to the eyepiece, allign the eyepiece to the camera before attaching the eyepiece to the telescope. Pointing the camera and the eyepiece at a light source can make it easier to center the eyepice. Once adjusted, make sure the mount is tight enough that under the weight of your camera everything stays in line.
  • Focusing the telescopoe can be very difficult. Depending on your target, it may be easier to focus on a bright star. Spend a lot of time to make sure you have good focus.
  • Center your target. Depending on the focal length of the lense and eyepieces used, with afocal coupling it is often very important your target remains center of the image. Sometimes there is a blind spot around the edges, or at the very least vignetting.
  • If your camera allows you to control the shutter speed select the one that gives you the most detail. You may want to look up in a chart, or use software such as the Afocal Coupling calculator (Eyepiece Projection Calculator)here.
  • Take as many exposures of your target as you can. As the atmosphere is always moving and blurring your images, the more images you take the more you can stack and correct for this. You can achieve sharper images this way.

    Procedure - stacking/processing the pictures

    Under contruction - author got distracted

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