10 inch Classical Caseegrain

[Merlin66 (Ken)]

The Gaviola secondary test doesn't require a master for interference comparison, only a std magnifying glass of similar diameter. Uses the Foucult/ Ronchi test set up. Well worth considering.

[Satchmo]

Cristian

As I imagine your Cass is F12 or slower speed , I'd recommend do the final figuring on the secondary using a real star with a Ronchi grating and the whole telescope assembled. At F12 or slower beam the Ronchi grating at focus would be a fairly sensitive test ( but not that useful at F5 or faster ) .

Mark

[cristian abarca]

Thanks Mark that is the final test that I will perform. (I haven't finished the telescope yet, still waiting for gears for my mount from the US) At the moment I just want something to tell me that I'm heading in the right direction with the polishing. It's like driving blind I can't tell if the figure of the mirror is heading towards spherical or not. At this stage I've never managed to make a mirror that is spherical after polishing, there is always a slightly TDE or a slight hole or hill in the centre. I like to test as I'm going along and modify my stroke accordingly so that I don't end up with a really bad figure. The first mirror I made took me about 12 hrs to fix and it was touch and go whether I went back to fine grinding or try to fix it. I persevered and finished it but since then I have become a little paranoid and like to check after every hour of polishing. I don't trust my strokes maybe I should I've done enough of them.

Regards Cristian