Light enters a telescope through an opening at one end. Usually there is a lens or corrector plate at this opening but in some cases, as with Newtonian telescopes, there is only an open end. Light reflecting off of the inside of the telescope tube reduces the effectiveness of the scope by producing glare, reflections and ghosts. These aberrations can be corrected by placing baffles inside the telescope tube to intercept the reflected light and keep it from reaching the eyepiece. Baffles help improve the quality of the image by allowing only parallel light rays to reach the viewer's eyes.
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Things you need
- 1/8 inch thick, matt-black poster board (larger than the diameter of the telescope tube)
- Circle cutter
- A steel square or carpenter's square small enough to insert into the telescope tube
- Flat black paint
- Small paint brush
Disassemble the optical tube assembly (OTA) of the telescope so that you can inspect the interior without any obstructions. This may require removing a lens or corrector plate at the front of the tube so ensure that the lens or corrector plate is safely stored while you insert the baffles (you will be waiting for glue to dry).
Measure the inside diameter of the OTA and the length of the tube from the front opening to the mirror (on Newtonian telescopes, Schmidt-Cassegrains or Maksutovs) or the draw tube (on refractors). Divide the length of the tube by the diameter and subtract one to determine the number of baffles you will need. For example, if the OTA is six inches in diameter and 60 inches long, you will need nine baffles.
Cut the required number of circular baffles, matching the inside diameter of the telescope tube, using a circular cutter. Cut the centre out of each circular baffle, producing a ring that is 1/4 inches deep.
Beginning with the farthest or deepest ring position, glue each ring inside the telescope tube an equal distance from each other. Do not attach a ring at the very edge of the telescope tube, where the lens or corrector plate will be reattached. Use a steel square or carpenter's square to true each ring and ensure that each one is perpendicular to the axis of the tube.
Allow the glue to dry completely and then apply a light coat of flat-black paint to the glue joint. Touch up any nicks made inside the tube that may expose bright metal. Reassemble the OTA and the telescope is ready for use.
Tips and warnings
- For telescopes that do not allow the removal of the mirror, work with the telescope elevated and angled down so that if you drop a tool it does not fall onto the mirror.
- Place the baffle and true it before applying a light bead of glue. Use only enough glue to hold the baffle in place (the baffle will not be under stress).
- Never look at the sun without special solar filters because it may cause permanent eyesight damage.
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