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Pretoria Centre of the Astronomical Society of Southern Africa

ScopeX ATM report

General view of Pretoria Centre stand and member's telescopes Johan Smit talking to a visitor

General view of the venue Johan Smit with his demo telescope

ScopeX is the annual astronomy fair of the Johannesburg Centre of the ASSA. The 7th ScopeX fair took place on Saturday 24 May at the Military History Museum in Johannesburg. Several members of the Pretoria Centre of the ASSA received prizes at the fair for the telescopes they built. The following excerpts were taken from the July 2008 newsletter of the Johburg Centre.

“Percy Jacobs received a 6.3mm Plossl eyepiece from Telescope SA for his 10-inch Dobsonian which, despite a moderately fast f/ratio has very good optics - especially for one so new to the hobby of mirror making. I believe that his satisfaction in the views he enjoys while observing is eclipsed only by his delight at star-party visitors consistently returning to his telescope, saying that they prefer the images it renders to those of rather more expensive (and larger) commercial instruments on the same field. Sadly, just a week before ScopeX, Percy managed to break the secondary mirror for the 6-inch Scheifspiegler he is constructing, this just as he had finished figuring it. Hopefully we will see the completed instrument at the next event.”

“Danie Barnardo received a green laser pointer from Eridanus Optics for his 6-inch Dobsonian with good optics. His observing chair is of basic construction but eminently functional and noteworthy as being something others can easily replicate; without it, the low telescope would be incomplete. Being able to observe in convenient comfort adds immeasurably to the experience. Taking the trouble to put together a total observing system is highly recommended.”

“Pat Kuhn also received a green laser pointer from Eridanus optics, for his observing system that similarly comprises a 6-inch Dobsonian with good optics and a fine observing chair built on kinematic principles, but includes in addition a microprocessor-controlled equatorial platform for tracking. Pat has a certain touch; everything he builds combines carefully-selected basic materials to end up both good looking and highly functional.”

“Fred Oosthuizen received a 40mm Plossl eyepiece from Telescope SA for his Caustic Test setup. The tester is a precision instrument, with tolerances constrained to but a few thou where appropriate. Many subtle features, some difficult to implement and others so simple one wonders how come nobody else has thought of it before, combine to facilitate single-person setup and operation. We look forward to viewing through the fine mirrors that should result from this painstakingly meticulous approach to testing.”

Paul Marais is not a member of our Centre, but since he is from our side of the Jukskei river (the civilized side), I think he has to be mentioned also.

“Paul Marais received a 15mm Plossl eyepiece from Telescope SA for his Dobsonian on an equatorial platform. Paul, working with basic hand tools on his farm near Magaliesburg, finished a working scope in short order with minimum advice and supervision. Interestingly, the few electrically operated devices involved during this process were powered by a wind generator he constructed himself from scratch. A notable innovation, simple though it may seem to the uninitiated, is provision for altitude/azimuth adjustment of the platform, incorporated into the leveling mechanism in order to facilitate polar alignment. Anyone who has struggled with polar alignment will instantly recognise the benefits and wonder why such features are not built into all platforms.”

The following paragraph was also added: “It seems to be a trait of the Pretoria contingent to pay extra attention to the quality of their mirrors. Generally they seem to be prepared to go the extra mile, performing the proper but timeconsuming mathematical analysis required to quantify the surface accuracy, rather than being content with a qualitative Foucault test assessment. This dedication pays off and is certainly to be commended.”

Editor’s comment: The last paragraph certainly is a big compliment to the abovementioned ATM’s. Congratulations to them. I hope other members of our Centre will follow their example. Fred Oosthuizen is also busy building an unusual type of telescope called a Stevick-Paul Schiefspiegler.