Scope Check Using Resolution Target (SCURT)

Quickly check your scope’s performance
 from any of the TSP fields!

TSP is resurrecting one of its great features from the early 1980s…. an illuminated resolution target that is mounted high on a nearby mountain.

  • Determine the resolving power of your telescope!
    • When: Ideally when your scope has cooled-down, and air turbulence to SCURT is lowest.  At least an hour after sunset!
    • Point your scope at the target, and obtain best focus using highest power eyepiece that you typically use.  Later you can try other powers/eyepiece types to see if there is improvement
    • Inspect the various vertical line groups and determine which group element’s lines are not resolved and use the next highest group element whose lines are just barely resolved.
    • Use the corresponding Group number (in red) and Element number within that group (in blue)
    • Repeat same, using horizontal line groups.
    • Note the number of the lowest resolved group element  for horizontal and vertical lines
    • Use the look-up table to convert your measurement into arc seconds
  • Our thanks to the TSP ATM organizers for their efforts to bring this project to reality, delivering a very useful benefit for our attendees!

  • Compare your scope’s resolution with your friends and neighbors scopes!
  • Check the collimation of your telescope and adjust as necessary.  Then recheck your scope’s resolution  to see if there is an improvement.
  • Works when cloudy! We will turn the target on as soon as dusk comes and the air starts to steady. Once the temperature across the ranch has settled you should be able to use the target, whatever the sky conditions!
    • Are you an astro-imager?  Check the effectiveness of your imaging setup, and record/compare various images and system settings.
      • See this closeup example, which is resolved to Group -1, and element 3.  You can just make out the black lines. (element 4 is not clearly distinguished.)

Located near the SCURT will ALSO be an artificial star.   This can be used for focusing and alignment when there are no usable stars.  


And now we have introduced SCUDS – Scope Check Using Double Stars.  Up on the hill near the other  targets you should see a small vertical array of 13 artificial double stars, ranging from about 0.2 to 2.5 arc seconds separation. These will look slightly different depending on where you are located, so use the look-up table to tell you the separation. The photo to the right shows the array, but the stars are out of focus. They are actually just 50 microns in diameter!
Have a go at seeing how close you can separate the artificial doubles, and perhaps see how it compares with the measurements made with SCURT.



  • Usage Notes:
    • Suitable for just about every scope (3″-36″) & observing position!
      • Because the resolution test targets are bars, keen observers or imagers should be able to resolve better than the Dawes limit [4.56 arcseconds/objective diameter inches], which really applies only to point sources. So we have catered for everyone, whatever their telescope, collimation and eyesight!
      • The bar targets presented will cover angular resolutions from 4 down to 0.05 arc seconds, most telescopes should resolve in the range 1 arc sec (a 4” refractor) to 0.2 arc sec (a 25” reflector).
    • Use our handy charts – we’ll have our All About SCURT handout at the Registration table

      • Pick correct table, depending on which field you are using.  Central field, Upper, or Southern observing fields
      • Look up your scope’s resolution (in arcseconds), using the smallest group/element you were able to see.  
      • Compare with theoretical limit Table (again, based on primary size)
      • Large central obstruction (secondary mirror) will degrade performance.
      • The resolution of your particular scope may be known (Obsession for instance publishes theirs on the web), or we will help you calculate it at TSP.
    • On arrival, take care to place your scope where you can see the target! (see positions of trees in photo below)
    • Consider these TSP Resolution Challenges!
      • Does the measurement change from night-to-night?  How much change during daytime?
      • Is it affected when changing/removing components in your system?  (diagonals, eyepieces, your glasses)
      • How much change with slight/major changes to your scope’s collimation?
      • How much does it improve when John Wagoner sets up his scope next to yours?  Why?
  • Post your comments to the TSP ATM Forum!


A view from the mountaintop Target, looking back at the TSP fields