[astro744]

Originally Posted by OzEclipse

Hi John,

My mirror is a 6 inch f7. I asked Palmway to apply both an enhanced aluminium coat plus a SiO overcoat on it. From memory I paid some tens of dollars to freight it to them, then they invoiced me $420 to apply the two coats to the primary and diagonal and freight back to me.

My mirror was originally hand ground polished and figured in the 1970's under expert mentoring by the late Cliff Duncan. The deal was that we we finished when he said it was finished not when I said it was finished. The scope had both sentimental value and the optics are really excellent so for me it was worth the expense. I would not re-coat a mediocre mirror.

I agree that the large Coulter optics mirrors in the 13.1" and 17.5" dobs were often not great, however Coulter also produced some very high spec optics at that time. The 12.5" Coulter cassegrain in Arthur Pages observatory at Mt Tamborine had incredible optics. So, I didn't make any assumptions about the quality of the OP's mirror but in my post I did make the point that my mirror is of excellent quality and so the added expense was worth it to me.

Joe

Very well said.