John Carmichael wrote: > Hi Ross: > > > >A little, off-the-wall, query. The larger the distance from the pinhole to > >the > >white sheet image of the sun, the larger the sun, but also the dimmer too. > > This is correct. The sun's image becomes quite dim at the long distance > needed to see sunspots. This can be corrected by lowering the amount of > ambient light as much as possible. Providing extra shade around the whole > setup helps. ie. use a large piece of cardboard for the pinhole, or put the > pinhole in the bottom of a box or tube.
Why don't we re-invent the "camera obscura"? :-) - fernando > > >Getting a small, very long focal length lens (or mirror) to replace the > >pinhole > >can solve the problem, at the risk of introducing some image aberrations, > >including chromatic, visible at the edges of the solar disk. This was of > course > >used to great effect on Kitt Peak in the wonderful solar telescope there > >that I > >visited a few months ago. > > > >The question is one of whether you or your astronomer friends knows of an > >optical system which produces the effect of a long focal length, but with a > much > >shorter distance from the optical system to the focal plane. > > Sounds impossible to me, but I'll ask my astronomer friends. > > Take care, > > John > > > > >John Carmichael wrote: > > > >> A bunch of us, including astronomers from Kitt Peak, traveled to southern > >> Baja for the July 11, 1991 total eclipse. > > > >Thanks, > > > >Ross McCluney > > > > -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
