Courtesy of
Sky & Telescope
March 1994

SINNOT'S SLANT

One English Amateur's Legacy

by Roger Sinnott

     Every so often an amateur telescope maker hits upon an idea so revolutionary and handy that manufacturers take note. It's not that way in most other fields, at least in the 20th century, where research and development has become as much a profession as manufacturing and marketing. There is no Stellafane event for amateur telephone makers. Newspapers don't carry stories about home-brew flu vaccines concocted by amateur doctors. I hope I never read about an amateur's experiments in nuclear engineering.
     Tinkering with telescopes has been the lifelong passion of English amateur John Wall, who lives in Dartford, Kent. We featured him on the cover of of our February 1964 issue with a 12-inch reflector he had built for the Crayford Manor Astronomical Society. A few years later, while completing a 13-inch comet seeker, he came up with a novel eyepiece holder based on kinematic principles. Four ball bearings and a friction roller engage the drawtube at five points, leaving only one degree of freedom: smooth travel precisely parallel to the telescope's optical axis. He dubbed his device the Crayford eyepiece mounting.
     In the early 1970s Wall's invention quickly spread among other British amateurs. It received international attention when I wrote it up for this magazine in September 1974. Every year or so thereafter, a homemade Crayford has turned up at meets like Riverside in California or Astrofest in Illinois.
     The beautiful machining of JMI's motorized Crayford echoes that of the original three hand-controlled models made by Wall. And what has the Dartford telescope maker been up to lately? In a letter last summer he described his 32-inch reflector one of the largest amateur telescopes in Europe with a tube and fork mount composed almost entirely of slotted-metal angle sections. "These seem largely ignored as a telescope-making material," he writes, "yet they are far superior to wood and easier to manipulate." We can only guess what he'll tackle next.