215mm (8.5-inch) Ultra-light Binoculars

by The Bolton Group

No sooner were the 12-inch binos finished then Gerald looked around for a new project. The aluminium cut outs from the 12-inch binos were big enough for 8.5 inch ones so the temptation was too great. The 12-inchers are great for a star party or serious observing but for just carrying out easily for a quick view something lighter is needed. Hence these ultra-lights!

The finished binoculars at Kelling Heath 2008

Brian made the optics (6 mirrors) and Gerald the tube assemblies although Brian did make some of the parts including the focuser.

The binos have been designed to be ultra-light. The total weight including optics is around 65lbs.

All design goals have been met, ie:-

1. Ultra stable
2. Hold collimation
3. Simple inter-ocular adjustment
4. Easy one-man assembly
5. Easy one-man move

They dis-assemble into 4 components for easy transport and storage. All assembly thumb-screws are captive to avoid loss or accidents!

The views are stunning with pin-point stars and that magical 3-D effect! Just sweeping the Milky Way is a never to forget experience.

top end

Being the 3rd pair made by the group the design is now much refined and improved. The following pictures give some idea of the amount of work and precision that has gone into this unique instrument..

Parts 1

Parts 2

Parts 3

Optics - the 6 mirrors before aluminising

The optics are f/6 and all the mirros were made Brian. They are as usual to his very high standards - if they are not perfect he will not let them out of his workshop! Brian has made many many mirrors of all shapes and sizes. He recently completed a commercial contract for a large test mirror for a company specialising in lasers.

Bottom cage

Top cage

Central fork mount

To save even more weight the bottom bearing uses a circular rebate in both the upper and lower bearing plates. This is filled with over 100 ball bearings which provides a very wide track for stability plus low weight. It works a treat.

In this new design, the azimuth and altitude axis shafts have been left exposed for the possible option of fitting digital setting circles.

Inter-ocular adjuster

I hesitated to show this new idea. Our original 8-inch binos featured crayfords for adjusting the inter-ocular distance. Low and behold when commercial binos appeared a couple of years or so later they too had them! Coincidence?
This new solution was not suitable for the 12-inchers as their eyepieces came out at 45 degrees. However, with the smaller size of the 8.5 inch ones we have gone back to inline focusers so some lateral thinking took place. The adjustment only has to be 15 mm maximum - eye separation doesn't vary all that much. Brian devised this method with a single rotating knob (red) to adjust them in synchronisation. The focusing is helical - the black and brass units.

Brian and Gerald

The designers/makers - Gerald and Brian

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