Dave's 16 Inch Binocular Telescope Page

Building a large aperture binocular telescope has many parallels to other large projects such as building a house. You have a budget (or think you have), some initial ideas, a few pipe dreams and you have a blank piece of paper with an empty section. However on your side you also have a vast wealth of human knowledge from all of the others who have trodden on this path before you. Reading books and magazines, seeing photographs visiting Star party's to touch, feel and glean insights of other peoples triumphs and mistakes. One such book for budding telescope makers is called ”The Dobsonian Telescope” a practical manual for building large aperture telescope's, by David Kriege and Richard Berry. Any reasonable number of pivotal ideas were gleaned from building the 12.5 in. telescope from this book several years before. This book belongs on all telescope builders shelves.

As with any thing in life, it's all a matter of balance. In the case of building a large binocular telescope this is literally the case. Upon the building the first version of the top end of the telescope, with two large rolled aluminium tubes everything was fine until they were put on the Scales. Weighing in at almost 13 kg and with the 30 millimetre plate glass mirrors at the bottom end only weighing 8 kg each the centre of balance and hence the diameter of the side bearings would have been truly huge, almost one and a half metres. Back to the drawing board. An ultra lightweight, single ring top end provided the solution.

Walking the walk

The word building doesn't really do justice to the journey that began when David first saw that photograph of Clive Milne's 20 in. binocular over one year ago. Building merely implies the physical construction of something that has been designed and thought out already. Where as in reality it was a huge learning path for the constructor. What is interocular spacing, how do you achieve the merging of two separate images in the two eyepieces, can you spell co-collimation, do you need rotational adjustment on the tertiary mirrors. The answers to these questions, or the fact that they exist at all, is probably the reason that every telescope has not been built as a binocular. The advantages of the binocular are so huge, but few take up the challenge. David believes however that using some reasonably minor variations to his current design (for ease of construction) he could make a recipe book type approach to building large binocular telescope's a reality.

Availability of parts?

Some people would argue, that truly making your own telescope means making everything almost down to forging your own bolts. Of course this isn't practical, a reasonable number of the parts needed, including focuses, secondary mirrors and holders and pole clamps are readily available commercially. When it comes to primary mirrors only a small number of people have the ability to successfully manufacture a well corrected 16 in. mirror, let alone two perfectly matched 16 in. mirrors so these were also ground by a professional, Mark Suchting in Sydney Australia. A few of the parts required specialist machining but with some clever redesign work this could easily be eliminated.

Manageability

One of David's design criteria was the ability to transport this giant binocular in his 1600 CC Toyota Corolla four-door sedan. He almost succeeded, everything can indeed be transported in this vehicle but with only inches to spare and needing to be a contortionist to move the heavy boxes into position a $600 replacement vehicle, now affectionately known as “The Wreck”was purchased for the purpose. The heaviest part of the telescope weighs in at approximately 35 kg and needs two people to left it in and out of the vehicle. With the total weight of the instrument being 77kg Assembled it is an imposing sight it would seem almost large enough to create its own weather patterns.

Factors of size – i.e. anything needed doing completely differently because of large size?

As things get larger the amount of bending or flexion increases dramatically. Doubling the length of a pole for instance increases the flexion by a factor of eight. As the rocker box was over one metre long and not supported by the ground board for quarter of its length out of each end, it was made using a box sandwiched construction making it over 70 millimetres thick, it is now a solid as a brick water closet. This also allowed for a hollow cavity in which to place the motors and electronics for the ServoCat goto and tracking system.

Finished Cost and total time taken.

The finished cost for this project was somewhere in the order of NZ$10,000 it was hard to get an accurate picture because several tools including drills, saws, sanding machines and wood routers were purchased at the same time. From firstly seeing photographs on Mark Suchtings stand until first light was one year and one week exactly. Most of this time involved thinking, planning and revising, not building.

Mass producing?? (Ha Ha!)

Currently David has no plans of mass producing this instrument. Although ideas for a much simplified version that anybody could build for the reasonable price using commercially available 10 in. mirrors to make the wonder of true binocular version available to a much wider group of people are progressing very well Photographs…...John D. /Gary Beal

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