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Sun Projector

 

 

 

 

Observing and recording Sun spots is an interesting part of our hobby.  There are many different ways to observe the Sun safely.  Before you start, do some research. Learn how to observe safely. You can be permanently blinded by the SUN's powerful light.  

REMEMBER: Never look directly at the SUN without the right equipment.  Never use a telescope or binoculars to look at the Sun without the proper filters.

I wanted a telescope to observe Sun spots. This telescope needed to be:

  • Easy to setup
  • Usable for Public Observing Parties
  • Safe, even with small children around
  • Easy to point
  • Manually Operation
  • Low cost

 

 PROJECTED IMAGE

After doing some online research, looking at what others have done to observe Sun spots and consulting with a lot of ATM'ers that are much more clever than me, here is what I came up with.  It looks complicated, but it is just a folded refracting telescope that projects an image of the Sun and its spots on a sheet of white paper.  Projection is a "tried-and-true" method for looking at Sun spots and it is SAFE.

 FINAL PLANS COLOR
 FINISHED FRONT LABELED

 

Folding the refracting telescope places the projected image on a flat and shaded surface making it easy to see.  A "must-have" for public events.  

The objective is arranged so that it points up at celestial north. 

To set up, I simply align the base of the Projector so the back end faces North.  Then I adjust the 4" flat mirror tilt angle for the day.  After that, the forked bracket holding the tilted mirror needs to be turned periodically to track the Sun the rest of the day.  I rotate the bracket once every few minutes manually.  

I may added a low cost light timer to rotate the lazy susan mounting bearing at a rate of once/day.  This would provide "hands off" tracking.  [Light timers are a cheap source of one revolution/day motors.]  

This may be a complication I don't want.  Explaining why I need to move the backet once in a while helps the public remember that the earth turns, hence the Sun appears to move through the sky.

  

 

 

I decided to build the Projector using many of same materials and construction details used to build my Schiefspiegler off axis reflector.

I cut out the side panels from a 2'x4' Luan sheet first.  Luan is sometimes call "door skin" and is between 3 and 5 mm thick.  Nice and light.

 SIDE OUTSIDE
 SIDE INSIDE

Next the side panels were trimmed using 3/4" square pine.  I used wood glue and small finish nails to do this.

 

The final assembly is quite stiff, but remains light weight too.  The picture to the right shows all major parts fit and in place.  ROUGH ASSEMBLY
 REAR VIEW The open back provides good shade for the projected image of the Sun but also allows several observers to see the projected image at once.
I used two coats of one step Polyshade. This provides enough wood sealing to protect this project for a long time.  [It is unlikely this unit will be exposed to much dew and/or rain.]  FINISHED FRONT
 FINISHED BACK

 

 

The size of the projected image can be adjusted by changing eyepieces.  Shorter eyepiece focal lengths produce a larger image.  The size of the image can be calculated using this equation:

           Diameter = Distance/107 x (M-1)

where:

  • Diameter = Size  of the projected Sun image
  • Distance = Distance from eyepiece to the surface.
  • M = Magnitude of the Telescope
  • [Magnitude = Focal length of the objective divided by the focal length of the eyepiece. But you already know that one.]
  • All units of distance, focal lengths and image size must be the same.

This Projector has a 50 mm objective with a focal length of 600 mm.  With a 13 mm eyepiece,  M=46x.

therefore:

Diameter = 9.5" * 25.4/107 x (46-1) ~ 101 mm 

Roughly 4" in diameter.