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Pinholes in Coatings?

Started by dj123, 08/05/2005 12:01PM
Posted 08/05/2005 12:01PM Opening Post
I have read that all coatings have pinholes. Is this about normal?
20x view of my 3.1" Discovery secondary. The area shown is about the center, the pinholes get worse towards the outer edges. This secondary has enhanced coatings and was purchased new in Oct 2004. As I have nothing to compare with I don't know it this is average for enhanced coatings. The pinholes can not bee seen without magnification. I'm having it recoated with standard coatings as I'm also having my primary refigured and recoated.

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dj123's attachment for post 25920
Posted 08/05/2005 01:19PM #1

As far as I know, all mirror coatings have pinholes in them. Don't worry about it and just use it. If it takes 20x to see them, I would say you have better than average coatings.
Posted 08/05/2005 01:28PM #2

I forgot to mention, I would never put standard coatings on a secondary mirror. I can't think of one company that make secondary mirrors that don't use some kind of enhanced coatings.
Posted 08/05/2005 01:43PM #3
David,

I'm afraid your photo doesn't tell us a whole lot, since we can't tell how much of the surface you're showing us. How wide is the portion of the mirror in the photo, half an inch? Two inches?

Despite what others are saying, all coatings do not necessarily have pinholes. Pinholes I believe are the result of not pulling a high enough vacuum in the coating chamber. My 8" mirror done two years ago by Spectrum has no pinholes.

The best way to look for pinholes is to hold the mirror up with a strong light source behind it. Pinholes will be obvious. IMHO if your secondary mirror has more than say half a dozen pinholes then it doesn't have a very good coating.

Doug
Posted 08/05/2005 01:54PM #4
Those don't look like pinholes in the coating, but rather in the over-coat. Pinholes, you see by looking at the backside of the mirror at a bright light. They show as bright spots where the light comes through.

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 08/05/2005 03:30PM #5
Looks like splatter marks to me. Caused during the coating process. Splatter marks (some call then spit marks) are little spherical nodules caused by too fast application of the overcoat.

Roland Christen