BAA/AAVSO Day 2: Observing the Sun with Small Scopes

Posted By Pamela on Apr 12, 2008 | 3 comments

The nearest star to the Earth is easily observed during the day. It just happens to be called the Sun. The problem is, it’s quite close and this can make it very hard to observe safely without hurting yourself or hurting your eyes. The current speaker, Lee MacDonald, is discussing several simple rules for attaining good results for anyone who wants to observe the Sun.

Basic Rules:

  • Don’t buy cheap filters or off brand filters. All because the Sun may not hurt to look at, you can’t know that it isn’t damaging your human optics until it is too late.
  • If you are using a Cassegrain telescope of some type (A reflector with a front end corrector lens and rear eyepiece), you must must must use an aperture filter to prevent melting of necessary plastic bits within your optical tube assembly.
  • Remember: When in doubt, project the image and look at the Sun on a screen instead of through the eyepiece

It sounds simply, but quite a few folks have lost an eye or two to the sun.


  1. Did he happen to mention a certain colorful thing about the Sun? Huh, did he, huh? hehe [I never thought I’d be a shill. It’s kinda fun.]

  2. The full aperture bit isn’t limited to Cassegrains. Take my 10″ Newtonian, for example. An eyepiece filter will take the full heat of the mirror, and even if it works, it will probably break – which would be extremely bad.

    Even with small refractors, eyepiece projection can damage the eyepiece – though at least blindness isn’t a problem.

    Back in the day, i used eyepiece projection with a small refractor for 1) an eclipse, 2) transit of Venus, and 3) transit of Mercury. These days i use a full aperture solar filter, from the manufacturer, designed for the telescope. It wasn’t the cheapest option, by a long shot.

    At night, i tell people to look at stars. In the day, i tell people to not look at the star. My finder scope is removable, and so, i don’t put it on the Dob during the day. Align by shadow.

  3. I have goofed around with pinhole projection. You need quite a bit of focal length to get much image size. Perhaps a long tube…

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