GAERTNER 10" COELOSTAT
AND PERKIN-ELMER LENS
Be sure and see the spectrohelioscope page

There is a lot of confusion between a Coelostat and a Heliostat. A Coelostat is a two mirror system that follows the sun and reflects an image of the sun that does not rotate as the Sun moves. A Heliostat can be a one or a two mirror system. (A page with my heliostat from the USNO Transit of Venus Expedition is here.) The biggest difference is that with the heliostat the image rotates as the Sun moves. This makes for some difficulty in photography. Visually, however, it makes very little or no difference -- unless you are sketching! Following are some pictures of my 10" Coelostat along with the interior cage that hangs from the ceiling. The cage contains two refractor type telescopes. One (76MM (about 3") F15)  had the cell and one of the lenses but the outer lens was broken. I managed to locate a Unitron lens which just fit the cell, and the focal length was also correct. The other one was missing the lenses and the cell. It was about a 2-1/4" F35. I found a 5-1/4" F15. It had some chipping on the edges, but that didn't matter to me as all I needed was the center 2-1/4". Pictures below should tell the story. So it is now a 2-1/4" F35. The smaller long focal length telescope is used to project an image onto a wall or the floor. The 3" is used to project an image to the two prism Spectroscope. If you move the two small refractors out of the way, the Sunlight (IT IS NOT AN IMAGE YET; ONLY PARALLEL SUNLIGHT) then goes to the Spectrohelioscope.

GAERTNER 10" COELOSTAT CIRCA 1930

The following images were taken of the equipment in "as found" condition, before any cleanup or restoration. More pictures will be added after this project is completed.

This is the primary flat mirror holder.
The wheel on top is a large worm gear and drive system.

   
The pier with mounting for the secondary mirror.
This reflects sunlight downward through the roof and ceiling to the cage assembly, below.

 
This cage assembly has two telescopes in it which are used to 1) project an image of the sun on a wall or floor, and 2) to make an image to project into the Spectroscope. These two telescopes may be moved out of the way in order to allow the 6" F50 lens to be swung into the path of the sunlight.

You can see the two large prisms in this picture of the spectroscope.

The 6" F50 Perkin-Elmer Lens

This lens has a very long focus, compared to a regular refractor lens. As you can see from the photo below, it has a 25 foot focal length. It is parafocal for two wavelengths, "C" and "K". I didn't realize just how lucky I was for a while -- this is made for Hydrogen-Alpha! (H-µ and Violet Calcium.) 

Not very confusing after you actually see what it means. Glass and other objects can bend light. This is called refraction. Hence the word refractor, as in refractor type telescope. Remember seeing a spoon or other object in a glass of water? It looked like the object was bent. This is refraction. 

Sunlight is made up of many different colors.  Colors are different lengths, so each will bend at different angles. The colors will be in focus in different places because of the different lengths. Water, as in rain or mist, also bends light and refracts it so we see a rainbow. This is why a rainbow has the colors separated - they are in focus, or refracted, in different places. A prism also has the same properties. Usually lenses are ground so that some wavelengths end up at the same place. So in this case, parafocal means two wavelengths or colors, "C" and "K" end up in focus at the same place. This is why some telescopes or binoculars have tinges of color around objects. Lens manufacturers make lenses with more than one piece of glass. Each piece refracts a different wavelength, so several wavelengths can end up at one focus.

This doublet lens produces a solar image 2-3/4" in diameter.

label on the 6" F50 lens

Same lens, showing the push-pull capability