At about the 12-inch size, it is more practical to switch to a truss-tube design, which we will not cover at this time (see for very good plans on building large aperture truss-tube dobsonians). there are many ways to build a dobsonian telescope, with many design decisions to be made.. Sooner or later reality took hold again and i thought that the truss tube idea could be applied to the primary and secondary mirrors i already had in my possession, namely a 150mm (6 inch) primary and a matched secondary mirror. i eventually discovered david kriege�s book about how to build the open truss type telescope.. In the final part of the series, we show you how to complete this exciting building project. download the original article and additional plans from our may 2014 issue coverdisc..