I am replacing my secondary mirror and the original shroud is not all that great. I seen on a web sight that you can lay the secondary mirror down on its face and spray flat black spray paint to cover the the edges. What should I do make a new shroud, or try the spray paint method? Thanks ahead of time for your thoughts. And clear skies.
When Mounting Secondary Mirror ?
Started by Dimpa, 03/15/2006 02:27AM
Posted 03/15/2006 02:27AM
Opening Post
Posted 03/15/2006 02:44AM
#1
I think by "shroud" you mean the thing that covers the edge of the secondary mirror. You are astute to note that the exposed glass edge will reflect unwanted light into your focuser.
I would use some silicone adhesive to glue a small strip of the darkest felt material you can find to the mirror edge facing the focuser. Protostar flocking material is what I used. Your spray paint idea is not half bad either. Just do something to cover the edge facing the focuser, and you will have done a lot to solve the stray light problem.
By the way, that silicone adhesive is great stuff, and can be used to mount the secondary to the spider. If you are concerned about it ever shaking loose, you should glue a short black nylon cord (e.g. shoelace) to the back of the secondary, loop it around a spider vane, and then glue the other end back to secondary to "leash" the secondary to the spider. Better to be safe than sorry!
Hugh Bartlett
I would use some silicone adhesive to glue a small strip of the darkest felt material you can find to the mirror edge facing the focuser. Protostar flocking material is what I used. Your spray paint idea is not half bad either. Just do something to cover the edge facing the focuser, and you will have done a lot to solve the stray light problem.
By the way, that silicone adhesive is great stuff, and can be used to mount the secondary to the spider. If you are concerned about it ever shaking loose, you should glue a short black nylon cord (e.g. shoelace) to the back of the secondary, loop it around a spider vane, and then glue the other end back to secondary to "leash" the secondary to the spider. Better to be safe than sorry!
Hugh Bartlett
"Praise the Lord for the expanding grandeur of creation, worlds known and unknown, galaxies beyond galaxies, filling us with awe and challenging our imaginations." 2007 Reform Siddur
Posted 03/15/2006 05:51PM
| Edited 03/15/2006 05:52PM
#2
If you wish to paint the edge of the secondary with flat black paint, you can lay the mirror face down on several stacked Kleenex tissues. The weight of the mirror will push the face of it into the tissues and protect them. Do not rub and make sure the mirror face is free of dust before sitting it on the face.
The trick is to spray the paint from about 18-24" away so that it just dusts the mirror not soak it. This produces a very flat and rough finish. You can uses a piece of paper cut to the shape of the mirror to place over the back side so it stays free of the paint.
Let it dry completely before moving the mirror. Do not spray too quickly, use many light coats not one quick one and the paint will not soak into the tissue and weep onto the front surface.
However, the other methods of eliminating the glare are also good.
Just thought I would elaborate on how to do the painting properly.
The trick is to spray the paint from about 18-24" away so that it just dusts the mirror not soak it. This produces a very flat and rough finish. You can uses a piece of paper cut to the shape of the mirror to place over the back side so it stays free of the paint.
Let it dry completely before moving the mirror. Do not spray too quickly, use many light coats not one quick one and the paint will not soak into the tissue and weep onto the front surface.
However, the other methods of eliminating the glare are also good.
Just thought I would elaborate on how to do the painting properly.
[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue
Amateur Imager
Posted 03/15/2006 10:18PM
| Edited 03/16/2006 04:17PM
#3
Painting the mirror will have some impact on how
you clean it in the future. Sometimes people use
rubbing alcohol to clean, but this will dissolve
Krylon paints (including Ultra Flat Black, a favorite).
Some people clean with acetone, but this will
dissolve most paints.
I know from experience -- I once used a Sharpie pen
to blacken the eyepiece edge of the secondary. Couple
years later I absent mindedly decide to do a quick
touch-up cleaning using rubbing alcohol and soon
had an awful mess with dissolved Sharpie ink all over
the front of the mirror. It all cleaned-up eventually,
but I would rather have been observing that night.
One strategy would be to use oil-based paint
(not Krylon) that is resistant to alcohol, and then
clean with alcohol. Or just leave it in the shroud.
you clean it in the future. Sometimes people use
rubbing alcohol to clean, but this will dissolve
Krylon paints (including Ultra Flat Black, a favorite).
Some people clean with acetone, but this will
dissolve most paints.
I know from experience -- I once used a Sharpie pen
to blacken the eyepiece edge of the secondary. Couple
years later I absent mindedly decide to do a quick
touch-up cleaning using rubbing alcohol and soon
had an awful mess with dissolved Sharpie ink all over
the front of the mirror. It all cleaned-up eventually,
but I would rather have been observing that night.
One strategy would be to use oil-based paint
(not Krylon) that is resistant to alcohol, and then
clean with alcohol. Or just leave it in the shroud.
Funding Member
