Eclipse2017

Idaho Falls

Dramatis Personae:

• Keith Lofstrom, MSEE UCB 1975, optical engineering team
• Dan Karlan, BSChmE MIT 1971, MSCS FDU 1973, construction engineering team
• Char Glenn, BSBio Duke 1970, MD OHSU 1995, principal photographer
• Steve Piet, PhDNuE UNC, gracious host
• and a supporting cast of dozens

• Viewing Box: ancient camera tripod, bed-board, cardboard box, ABS 2 inch pipe, InFocus projector lens, brand X macro lens, bailing wire, duct tape, chewing gum

  • pencil shadow and X on box, for alignment

This finely tuned optical instrument is aligned by twisting wires. Next time, add ballast and small sail to front for weight and wind balance, perhaps an old Tarheel yearbook from gracious host. Details below.

click images for larger view:

http://astro.ukho.gov.uk/eclipse/0412017/usa/usa_2017.html

Details - Building This Was Half the Fun !

While Dan and I tested this after we assembled it the day before the eclipse, we pessimistically assumed that the round white image projected was merely the unfocused light passing through the tube. However, there were black speckles in the middle, that sharpened as we turned the projector lens focus nob. Were the speckles artifacts? We rotated the tube and lenses; the spots did not turn with the lenses. Houston - we have sunspots!

Since we could see an array of sunspots, smaller than 0.5% of the Sun's projected disk, we were hoping we could see lunar topography the next day. However, the cheap objective lens, or perhaps the mis-use of the projector lens, created significant chromatic aberration, obvious along the edges of the sun images pictured below. Red dark adaptation goggles would filter out chromatic aberration and help with pre-eclipse dark adaptation - but who sells them???

Alternately, some narrow-pass red theater gel in front of the objective lens can accomplish the same goal. Perhaps blue theater gel would be better for visual resolution, and it would keep the infrared out of the optics, but it would provide less dark adaptation.

Some claim "all you need is a simple pinhole camera". That's only good for observing a crescent, not fine detail. If the projection surface is a meter from the pinhole, then a 0.5 millimeter pinhole creates only a 10 mm diameter, 20 pixel diameter image, illuminated at 0.3% Sun intensity. Our box was about 0.5 meters deep (and suffered from wind buffeting), and produced a focusable 500 pixel image at 20% Sun intensity. Yes, pinhole boxes are easy to explain to children, and adults who have learned nothing since childhood. Some of us aspire to more (and did, even as children), and thrill to walk in the same footsteps as Galileo and Kepler.