Monday, June 9, 2014

Orion ST80 Collimation

I've been following some tips online regarding tuning up the Orion ST80 budget telescope.
Here are the links I've been following:

Major steps taken:
  • Blackened the edges of the lenses.  Pretty easy, just remove the retaining ring and drop out the lenses.  Darken the edges with a Sharpie.  
  • Cleaned the lenses with microfiber rag with Methanol.  This is my preferred method for lens cleaning.  Does a nice job of removing fingerprints and pollen.
  • When inserting the lenses, I made sure that they were seated squarely by rapping the scope body while holding it upright.  Gravity ensured that the lenses rested solidly against the cell.
  • Collimated using airy ring test with my 7mm Nagler.  Even with two extension tubes, it didn't have enough travel to bring it to focus, so I had to let the extensions out a bit more.  I found that the optics were pinched even though I had them loose earlier in the day.  Temperature is a big factor!


Next major step will be to remove/cut/grind off the screws that protrude into the light path.  When looking at the bahtinov mask image, I can see lots of diffraction "curls" appearing.  I don't have a method to grind the screws, I may try fitting a different screw/bolt or press a dremel into service.

Future work may be to get a GSO focuser to replace the stock unit.  This would allow using a reducer/flattener on the scope, further tightening star images.

Already seeing improvement in star images.

Note how close the FWHM value is to "perfect" for this scope as referenced at http://www.calctool.org/CALC/phys/optics/spot_size