20+inch+F4+Dobsonian

The 20 inch F4 originally had a plate mirror 25mm thick. Nominal wave front was 1/3 wave PV. First light was at the LAS Wirral Country Park Star Party 21st March 2010.

The mirror was coated at Vacuum coatings in London the day before!! Total cost of the whole telescope was approx £650.

Axis motion of the telescope is perfect!....Optics are ok, but need tweeking below 1/3 wave for higher powers. But it is great for lower powers at public star parties.

It is easy to assemble and get around. It fits inside a Nissan Micra too!!

Since it was first built the telescope has gone through a few modifications including the mirror being upgraded to a 20 inch 42mm thick Pyrex blank (summer 2013). Note that the mirror is F3.8 now not F4.

Details on our efforts to complete the mirror are here:- http://paine1776.wikispaces.com/20+Inch+Pyrex+F3.8

Some images of the telescope are here on Dave Owens site too:- https://paine1776.wikispaces.com/20+Inch+Pyrex+F3.8+-+Image+Gallery

The top box has also been modified and soon it will be shipped out to Spain (Summer 2015) where Dave Owen has now emigrated to!! Nice dark skies for this telescope.

AutoCAD drawing of the telescope with 'improvements' built in for the next one we make. The CAD drawing still has some outstanding parts including the mirror cell.

Links to Dave Owens pages on the 20 inch F4
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http://lassa.wikispaces.com/20+inch+F4+telescopes

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Link to figuring the old plate mirror which has now been replaced as stated above. http://lassa.wikispaces.com/20InchF3.9+Figuring Plate mirror Couder mask measurements.

Some images of the telescope are below:-
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