astro-optics page my Coronado PST observations
wpo - Coronado PST quasi-equatorial mount + sunscreen
Adjacent is a scaled sunscreen template for the
Coronado PST made from 22" x 8" sheet of thin black card. It
fits between the PST 'tuner' collar and body and overlays the eyepiece
holder to screen extraneous light in peripheral vision. The sunfinder
and tuner remain effective.
Score card prior to folding.
Crawford-Dobsonian mount for Coronado PST for Ha observations: In the Brit.Astr.Assoc. Journal -1988 Aug v98,#5, p268/9 I described how the Dobsonian mount could be given a equatorial motion utilising a technique first used by the Earl of Crawford in the 19th century. A cord attached to the telescope near the eyepiece with the other end secured to the ground at a point in the north-south line serves as a declination clamp - see adjacent Dobsonian figure. A weight attached to the telescope tensioned the line which constrained the instrument to move in an equatorial arc tracking an object across the sky by just hand pressure near the eyepiece. A similar arrangement imparted equatorial movement to the Earl of Rosse's Great 72-inch reflector in Ireland in the mid 1800s and could be adapted to today's Coronado PST on a robust tripod with smooth pan-and-tilt head.The sketch above shows the principle eg a fixed bracket off the tripod head anchors a line [adjustable cord or rod shown blue] to a collar attached to the PST tube. A bracket attached to the collar forms the upper anchor point so that an imaginary line through to the tripod's horizontal/tilt axis is parallel to the PST's optical axis [shown green]. The observer's latitude is set by raising/lowering the pan-and-tilt head via the crank handle so an imaginary line points to Polaris [shown purple]. This crank could perhaps be used to make small adjustments to view the upper or lower solar limb by slightly shifting the vertical polar alignment.
As an alternative to a collar around the PST tube, the upper anchor point could be a bracket fixed to the tripod head or combined with a sunshield. Any deviation of the upper anchor point's offset from the PST tube as shown will cause the sun to drift out of view over time but can be adjusted by changing the length of the line linking the two anchor points from time to time. Once the tripod is carefully set-up the sun is tracked by applying slight pressure to the left on the tripod handle.
text & images [c] Maurice Gavin 2005
