A sun finder for a refracting telescope

Or, yet another use for a free pen. By Martin Whillock

sun finder

Finding the Sun for viewing in a telescope might seem to be easy, but it can be tricky.  The basic method is to move the telescope around until its shadow behind it is as small as possible. This is not always easy because of the background behind the telescope.

Take great care when looking at the Sun. A proper filter is essential, or use the projection method.  Never look directly at the Sun with a telescope or binoculars – instant blindness will result.

There are several simple designs for sun finders.  Here is one made for free from a length of 4″ drain pipe, a turned block of wood and a free pen.

With this design it is necessary for all the parts to be parallel to the telescope’s optical axis, this is achieved by

  1. The tube being a sliding fit over the Objective end of the refractor, and is relatively long.  I was lucky to find a bit of tube the right diameter.
  2. The turned block of wood being a push fit into the tube and again is relatively long.
  3. The hole for the pen being drilled on the lathe, making it parallel with the outside of the block and the pen being slid 4cm into the block.

In use the telescope is moved around until the pen has no shadow.  This gives close accuracy, which is finalised by adjusting the telescope’s pointing via the eyepiece and the mount’s hand controller.

When using this Sunfinder its best to keep your shadow on the Objective when removing the Sunfinder and replacing it with the solar filter, then add an eyepiece last.