Diagonal dropped on main mirror - ouch!

You are unlikely to notice any image degradation. Paint them black.

C.W. Thomas wrote:
My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Unfortunately, not in the center of the mirror...

Can I paint over these/ black them out with something without there being
major ramifications to the mirrors quality?

Yes.

I am concerned about weather this has caused stress areas surrounding the
pits that are signifigantly larger than the pits themselves.

Does anybody know anything about pyrex and stresses induced by impacts with
diagonals?

You don't want to get water or methanol in the fresh crack. Small
molecules can encourage stress corrosion cracking.

Beyond that something along the lines of epoxy or DPX ought to seal a
small defect and then spot it with matt black. It will only be a tiny
fraction of the area of the mirror that is lost.

Regards,
Martin Brown

I would take it outside tonight and test it's viewing on mars or something
else. I would think that small a nick on that big a mirror would amount to
next to nothing.


--

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"C.W. Thomas" wrote in message
...
My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking
it up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Unfortunately, not in the center of the mirror...

Can I paint over these/ black them out with something without there being
major ramifications to the mirrors quality?

I am concerned about weather this has caused stress areas surrounding the
pits that are signifigantly larger than the pits themselves.

Does anybody know anything about pyrex and stresses induced by impacts
with diagonals?

Thanks in advance;


C.W. Thomas

My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Unfortunately, not in the center of the mirror...

Can I paint over these/ black them out with something without there being
major ramifications to the mirrors quality?

I am concerned about weather this has caused stress areas surrounding the
pits that are signifigantly larger than the pits themselves.

Does anybody know anything about pyrex and stresses induced by impacts with
diagonals?

Thanks in advance;


C.W. Thomas

C.W. Thomas wrote:

My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Unfortunately, not in the center of the mirror...

Can I paint over these/ black them out with something without there being
major ramifications to the mirrors quality?

I am concerned about weather this has caused stress areas surrounding the
pits that are signifigantly larger than the pits themselves.

Does anybody know anything about pyrex and stresses induced by impacts with
diagonals?

Thanks in advance;


C.W. Thomas




Ouch is right. However all is not lost. As another poster stated you
should seal the chips and place a spot of black paint on the seal. As to
interfering with observation, some time ago mention was made of a major
instrument that has bullet holes in the main mirror that was still in
operation. My only concern would be for any scratches on the silvering
material or its protective covering. This might be a problem at sometime
in the future but not now.

Dave N

C.W. Thomas wrote:
My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Unfortunately, not in the center of the mirror...

Can I paint over these/ black them out with something without there being
major ramifications to the mirrors quality?

I am concerned about weather this has caused stress areas surrounding the
pits that are signifigantly larger than the pits themselves.

Does anybody know anything about pyrex and stresses induced by impacts with
diagonals?

Worse things have happened; you should be alright...

"one February night in 1970 a McDonald Observatory employee [...]
suffered a breakdown and carried a pistol to the observing floor of the
107-inch telescope. He fired a shot at his supervisor, and then unloaded
the rest of the clip into the primary mirror. Happily, fused silica is
more resilent than ordinary glass, and the big mirror did not break. The
craters have been bored out and painted black to reduce any
light-scattering effect, and the end result is simply a slight reduction
in the efficiency of the telescope. It is now the equivalent of a
106-inch telescope."

photos and commentry at
http://www.astr.ua.edu/keel/telescopes/mcdonald.html

Can I paint over these/ black them out with something without there being
major ramifications to the mirrors quality?

Yes. It will be like a very small obstruction. You won't see
much change if any.

I am concerned about weather this has caused stress areas surrounding the
pits that are signifigantly larger than the pits themselves.

I wouldn't worry about it. If it gives you peace of mind, you
might take it to the folks that repair windshield chips, but I
wouldn't worry about it.

Clear Skies

Chuck Taylor
Do you observe the moon? If so, try
http://groups.yahoo.com/group/lunar-observing/

If you enjoy optics, try
http://groups.yahoo.com/group/ATM_Optics_Software/
*********************************************

"C.W. Thomas" wrote in message ...
My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Have them grind you a new mirror

--

Hilton Evans
---------------------------------------------------------------
Lon -71° 04' 35.3"
Lat +42° 11' 06.7"
---------------------------------------------------------------
Webcam Astroimaging
http://home.earthlink.net/~hiltoneva...troimaging.htm
---------------------------------------------------------------
ChemPen Chemical Structure Software
http://www.chempensoftware.com

them who?


Hilton Evans wrote:

"C.W. Thomas" wrote in message ...
My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Have them grind you a new mirror

--

Hilton Evans
---------------------------------------------------------------
Lon -71° 04' 35.3"
Lat +42° 11' 06.7"
---------------------------------------------------------------
Webcam Astroimaging
http://home.earthlink.net/~hiltoneva...troimaging.htm
---------------------------------------------------------------
ChemPen Chemical Structure Software
http://www.chempensoftware.com

The perps.

Hint: read the first two words in
the C.W. Thomas' first sentence.

--

Hilton Evans
---------------------------------------------------------------
Lon -71° 04' 35.3"
Lat +42° 11' 06.7"
---------------------------------------------------------------
Webcam Astroimaging
http://home.earthlink.net/~hiltoneva...troimaging.htm
---------------------------------------------------------------
ChemPen Chemical Structure Software
http://www.chempensoftware.com

"Mild One" wrote in message ...
them who?


Hilton Evans wrote:

"C.W. Thomas" wrote in message ...
My boys accidentally knocked over my 12.5 inch F7 newtonian. In picking it
up, the Diagonal fell and struck the face of the main mirror (pyrex)
leaving a couple of small "craters" about 0.2" and 0.1" in length.

Have them grind you a new mirror

--

Hilton Evans
---------------------------------------------------------------
Lon -71° 04' 35.3"
Lat +42° 11' 06.7"
---------------------------------------------------------------
Webcam Astroimaging
http://home.earthlink.net/~hiltoneva...troimaging.htm
---------------------------------------------------------------
ChemPen Chemical Structure Software
http://www.chempensoftware.com