About the Project
The "Long Tom" is a group telescope-building project which was created several years ago by the SVAS-members'
email group, Although inactive for the past couple of years, Long Tom is now more than ready to be resurrected and completed. All members of the SVAS are invited and encouraged to participate in the building of a "club scope." Cary Chleborad has issued the following challenge to
members of the SVAS:
"I propose the telescope design to be an Obsession-style truss dob, with a few modern additions; such as a plop optimized mirror cell,
boundary layer fans, lightweight wood composite structure, a ball
and socket truss
connector, and possibly with a splash of carbon fiber composite work."
-Cary
Once completed, through the joint effort of donated materials and time by participants, Long Tom will be available for use by participants of the telescope workshop and local astronomy clubs at local public observing events.
WE ENCOURAGE YOU TO JOIN US ON EACH SATURDAY, CLOSEST TO THE FULL MOON, TO CREATE "LONG TOM" WITH US.:
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Project Specs 12.5" Inch Mirror ("Nugget") |
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 A Long Tom Sluice used in California |
Naming "Long
Tom" The Long Tom Telescope Project is named after the mainstay of the 1849 gold rush: The Long Tom Sluice. Long Tom is a fitting name for a scope built in the Golden State that will mine the heavens for astronomers' "gold." The name is also a good choice given the fact that the SVAS' primary observing site is just a few miles from one of the largest sluice-operated mines during the gold rush.
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More information about the "Long Tom" sluice: The Long Tom sluice (also called a "Broad Tom") was a modified sluice box. In its simplest form, it consisted of two sections. The upper section, called a tom, was a long trough in which the dirt was placed and acted as a large hopper. At the down slope end was a grating or screen, set at a 45 degree angle. The second section was a "riffle" box, with the upper end set under the lower end of the tom. The riffle box received the classified dirt that passed the screen on the tom. While water was directed into the upper end of the tom, the dirt was worked with a rake to break up any lumps of clay, clean off organic matter and knock any dirt from the rocks. The fine material flowed through the screen and into the riffle box where the gold was trapped behind the riffles. Operating a Long Tom sluice was usually a two or three man operation. |
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Optical Components
We've completed the mirror as a 12.5" F/10 (yes!! F10) and 2.125" thick. With that in mind we calculate the required secondary "diagonal" mirror using the Optic Wave Labs free diagonal calculator. We are making a pureley visual telecope dedicated to planetary (narrow field) viewing and a 1.25" focuser and eyepieces. After crunching the numbers we come up with the correct sized diagonal to order. We purchased the diagonal mirror, secondary holder and spider from Protostar.
Primary Mirror Cell
Having completed the primary mirror and chosen the diagional size, we downloaded and used David Lewis' PLOP to calulate the proper mirror cell specifications. We decided to use a 9 point cell, input the mirror parameters into the software and in a few seconds the proper cell arrangement and parts were calulcated. It's interesting to reflect how technology has advanced in just a few short years. The first tiem I used this software it took 14 hours to compute and optimize a mirror cell of this complexity.
Long Tom Gallery
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 Cary describes the Long Tom Project to the members at the February SVAS general meeting.. |
 John "launches" the project by giving the mirror ("Nugget") its first grinding session. |
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