Since the arriving of Dobsonians,all the mirrors seems to have gone to be thinner even the ones not intended for this type of telescopes.Does it means that the old 12.5 " and 60 mm thick mirrors like the mine are excessive and could be substitued by a lighter one with better results ? Where has gone all the advertisements on astigmathism of thin glass plates? has changed the kind of glass and now we can get the same quality with a glass plate?