Wednesday, November 23, 2011

Solar projection

I made a little cardboard solar projection box for my 8" Coulter, and a mask to cover all but 2.9" of aperture.  I read a hint to put two holes in to get the resolution advantages of the aperture--I may try that one day.  Or I might open up more of the aperture and use IR-rejection film, though that may be risky for the eyepiece.

It's easy to point the scope at the sun--you just move the scope until the shadow of the tube is as small as possible.  For safety, I make sure all the observers are on the side of the telescope away from the eyepiece.

With a 27mm Kellner eyepiece, after I got things into focus, the box did show sunspots.  (Note that the big yellowish smudge on the right is glue on the inside of the box, rather than a solar feature.  I will have to stick in a clean piece of card paper there.)  The image was actually a little too bright to view comfortable.  The photo of the projected image worked, though, once I set the camera to minimum aperture and exposure time.  I need to make some registration marks on the projection screen, so that I can take two photos in the future, one with exposure for the bright disc and the other with exposure for the registration marks, and use the registration marks to undo the skewing you see in the photo.

The sunspot positions match those here.

The aperture mask was quite warm, but the eyepiece didn't seem to get hot.

Solar observing safety precautions: Do not look through the eyepiece.  Do not look at the sun naked-eye, either.  Stop down the aperture to prevent the eyepiece from shattering from the heat (which is a waste of an eyepiece, and might cause harm from flying shards), and push telescope away from the sun every couple of minutes to cool off.  Don't use an expensive eyepiece.  Never use the cheap solar filters that screw into the eyepiece.  They can shatter while you're viewing and the sunlight is then likely to blind you (and I had one as a kid that faded with time--it got less and less dark! fortunately, I never used it in the telescope).


  1. This is a neat way to do Solar observing, thanks for sharing! I was curious, what material did you use for the mask?