Hi,
I am really looking forward to grinding my first mirror!
I have picked up a lovely DIY telescope made 57 years ago, and I would love to see it do another 57 years.
The mirror has an upturned edge and isn't in the best condition, so if I replace it, and put on a proper secondary (which I have simply ordered), I think it will be lovely!
I have ordered some texts to learn from (Jean Texereau's How to make a Telescope and Sam Brown's All About Telescopes), and have made some preliminary decisions - but having no practical experience, I don't know how well founded those are.
I am aiming for a 6" f/9 mirror 1/18 wave PV or better (aim for the sky, right?.. RIGHT?). I wonder if I can ever do that.
I was going to use just a glass blank (150mm (6") diameter x 25mm (1") thick), then make my own tools using plaster and tiles. But, I could get a Glass Tool 150mm (6") diameter x 19mm (3/4") thick at the same time I buy the blank - is that better?
For my grits, I was going to go Silicon Carbide 120, 240, 400, 600, Aluminium Oxide 800 then polish with Red Rouge (Yes, I know it's messy..)
I'm rather worried about the testing equipment. I think I can hang it on it's side and do a knife test, but I can't do much more, and I might need some help with figuring it at the end.
As far as grinding goes too, I don't have much to grind on - so I was thinking of trying to sit on a bench "John Dobson style".
https://youtu.be/snz7JJlSZvw?t=835
Is that okay?
I was going to follow his instructions somewhat for finding the focal length I need, as I need an f/9, but am also getting a spherometer to measure the depth accurately.
As far as the physical scope goes, I might be able to enhance it a little further. The current secondary is too large (It had a massive 1.8" diagonal
) and is obstructing too much light (30%). I am replacing it with a 1.3" (22%).
I can add some extra blackening behind the secondary too.
I was thinking of cutting some air vents into the bottom to expose the bottom of the glass to air, and perhaps create a cooling 'door' near the mirror.
Would love any suggestions or advice on grinding or any advice you might have. If you make mirrors and are around Logan, Brisbane, I'd love an email!