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Surface chips in an F8 Newtonian mirror

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#1 dgreyson


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Posted 13 December 2012 - 11:02 AM

Maybe someone can answer this question:

I have a 10" F8 newtonian mirror that I ground back in the 70's. So it has some personal noastalgia value. Back in the day, the secondary holder failed and let the diagonal mirror fall and knick two small pits in the surface. It would have only been one pit but it bounced so two small chips.

Still seems to work just fine, and a year or so ago I had it re-aluminized.

My question is this: Should I leave the pits shiny or should I paint them black?

and also, How signifigant a problem is this? Should I send it out to be reground? the chips are less than a wooden pencil diameter.

#2 Mike I. Jones

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Posted 13 December 2012 - 01:33 PM

Just blacken them with a black Sharpie and enjoy your scope. Based on your description, their area is so small relative to the primary's that they'll have essentially no effect on your image quality. The effect of your (new!) diagonal mirror shadow is hundreds of times more influential than your two little gouges.


#3 dgreyson


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Posted 13 December 2012 - 02:09 PM

Thanks Mike! That answers my question.

#4 KenScharf



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Posted 16 December 2012 - 03:38 PM

I've read that the 3 or 4 vanes that hold the secondary mirror holder are optically the same as double the number of diameter width scratches on the main mirror!

#5 JohnMurphyRN


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Posted 16 December 2012 - 03:44 PM

It would be really helpful if the chips were in the secondary's shadow...

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