Creating an Astro Image Part I – The Rig

An astrophotography rig is generally comprised of 3 major components : A mount, a telescope, and a camera.  For the most part, everything else “supports” one of those 3 things.

The mount is what moves the telescope (we hope) very precisely at the same rate as the stars travel across the sky, allowing us to take very long exposures of our target.  My mount is a Losmandy G11.

The telescope is the optical component of the system.  It gathers light, and delivers it to whatever device is “collecting” the light, perhaps an eyeball or in this case a camera.  My rig carries two telescopes, a Stellarvue SV80ST 80mm refractor, which is the main imaging telescope, and a Lunt LS50THa 50mm refractor, which is specifically designed for high end solar imaging.

At the “receiving ends”  of the two telescopes are the cameras.  The main imaging camera is an Atik 314L+ mono (yes, greyscale only!) CCD camera.  One of the “unusual” things about this camera (like many astro imaging cameras) is that it contains a small peltier cooler capable of dropping the sensor’s temperature ~20° C below normal operating temperature.  This helps reduce noise considerably.

The solar camera is a ZWO ASI120mc which has the ability to shoot video, which allows us to grab several hundred or even thousands of frames of a bright object like the sun or planets.

The guiding camera is a QHY5L-II.  The job of the guide camera is to take “short” (say, 2-4s) pictures of a particular star repeatedly, and deliver them to a piece of software that analyzes those pictures (see more on software in an upcoming post).  The software monitors the precise position of the star in the frame, and if it detects movement it issues a corrective command to the mount, to “keep it in line”.  Since even the finest of gear trains can have some level of error at times, the guide camera and guiding software helps correct of occasional issues in this regard.

The focuser is a Starlight Instruments FTF2525HD Feathertouch Focuser, and does exactly what you’d expect, focusing the telescope by moving the camera in and out very slight amounts.  It is motorized and computer controlled, allowing the imaging software to determine the ideal focus point for any given set of conditions, and move the focuser to that point.

The filter wheel is a Starlight Xpress Mini-USB Filter Wheel.  This unit holds 5 filters which allow us to produce color images from a mono camera.  Essentially, place a piece of red glass in front of a camera, and then tell your postprocessing software that the resulting greyscale image contains “red”.  Do this for Red, Blue, and Green, and presto…color image. 🙂  The filterwheel is also motorized, and the desired filter can be selected from the imaging software at any time.  This particular unit also contains a “pick off prism” to direct a small amount of light to the guide camera described above…this is known as “off axis guiding”.


In terms of “quality”, if 1 is “Cheapest thing you can find at a shady online retailer”, 5 is “pretty typical for the breed”, and 10 is “lovingly hand crafted by 500 year old Elven masters”, then :

  • Mount – 7
  • Sv80ST – 8
  • Lunt Solar Scope – 8
  • Main Camera – 4
  • Guide Camera – 5
  • Solar Camera – 3
  • Filterwheel – 6
  • Focuser – 9.5 (journeyman elves)

Next time, we’ll look at the software that manages the beast. 🙂

 

 

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