BAFFLES

Baffles are use to suppress unwanted light. Mostly they consist of a sheet with a circular hole in it. The used light passes through the hole. Baffles are placed in the tube and in the focuser. (See "Focuser Baffling" and "Tube Baffling")

To get an overview of what needs to be baffled, lets take a look from the entrance lens of the eyepiece via the secondary and the primary out of the telescope. In the worst case it looks as follows.

In the above figure:

  1. The figure only serves to illustrate the principles, it does not show the correct proportions.
  2. It only shows the view as it would be on the optical axis, for a correctly collimated scope.
  3. The off-axis view would not show concentric circles.
  4. In zone 7 we see the inside of the focuser tube this cannot be avoided, it must be made as unreflective as possible.
  5. In zone 6 we see the walls of the tube opposing the focuser and the secondary edge & support. This zone should be made as small as possible by baffling the focuser. The part of the tube wall that is seen should be made as unreflective as possible, as well as the secondary edge & support.
  6. In zone 5 we see the tube wall between the focuser and the backend of the tube. This should be made as unreflective as possible, maybe by the use of tube baffles.
  7. In zone 4 we can look out of the backend of the tube (this is not present in all designs). It should not be possible to look out of the tube. Place a baffle to prevent this. (Note the baffle should be placed behind the mirror.)
  8. In zone 3 we see the walls of the tube between the primary and the tube front end. See zone 5.
  9. In zone 2 we see the object we've aimed the scope at. This is the only light we actually want to see (gray area).
  10. In zone 1 we can see our eye. Prevent light from entering the eyepiece, since it will come back to us!. (this is probably not a real problem :-)

Although not a subject of baffling, we might as well note now that the edge of the primary (and maybe the secondary also) is probably the worst part of the mirror. Mask it off by placing a mask directly in front of the mirror. (Or paint it on) At least the beveled edge should be masked.

For instructions on how to baffle the focuser, see "Focuser Baffling".