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Why a Helical Crayford?
Helical focusers have long been the answer to a low profile Newtonian focuser. One of the problems has been the annoying slop in the threads. Another problem is the lack of a travel rate fast enough for accurate focusing. Most helical focusers have a single thread which limits the travel per turn to about 0.125". With multiple lead threads, the rate can be increased somewhat, but still falls short of the necessary rate.
This Helical Crayford design permits a fast rate, smooth feel, no slop, and backlash free performance in a simple, lightweight design. Also, the HC-2 has no grease to collect bugs or get stiff in cold weather.
