20" Lens Blank--Need Info

Our small science museum recently received in a very roundabout way a 20"
dia. clear lens blank. It's about 1" thick and is in good shape. We'd like
to give it to someone who can use it in the Sacramento, CA or Reno, NV that
can put it to a legitimate astro use. If not, then perhaps we could sell it
and use the funds for the museum's astro fund. I have no idea what it's
worth, but perhaps there's some way to find out? I can provide pix. There
are really two parts. The lens and a cell. The latter looks like it has
quite a bit of copper in it. Both are very heavy.

--
Wayne Watson (Nevada City, CA)

Web Page: home.earthlink.net/~mtnviews

To bad I'm so far away, it soulds like it could be turned into a mirror with
some grind of it, I'd lay odds that John Dobson could do that in a few days.
is that glass a lens or just flat glass?


--
There are those who believe that life here, began out there, far across the
universe, with tribes of humans, who may have been the forefathers of the
Egyptians, or the Toltecs, or the Mayans. Some believe that they may yet be
brothers of man, who even now fight to survive, somewhere beyond the
heavens.


The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html


"W. Watson" wrote in message
...
Our small science museum recently received in a very roundabout way a 20"
dia. clear lens blank. It's about 1" thick and is in good shape. We'd like
to give it to someone who can use it in the Sacramento, CA or Reno, NV
that can put it to a legitimate astro use. If not, then perhaps we could
sell it and use the funds for the museum's astro fund. I have no idea what
it's worth, but perhaps there's some way to find out? I can provide pix.
There are really two parts. The lens and a cell. The latter looks like it
has quite a bit of copper in it. Both are very heavy.

--
Wayne Watson (Nevada City, CA)

Web Page: home.earthlink.net/~mtnviews

"W. Watson" wrote in
:

Our small science museum recently received in a very roundabout way a
20" dia. clear lens blank. It's about 1" thick and is in good shape.
We'd like to give it to someone who can use it in the Sacramento, CA or
Reno, NV that can put it to a legitimate astro use. If not, then perhaps
we could sell it and use the funds for the museum's astro fund. I have
no idea what it's worth, but perhaps there's some way to find out? I can
provide pix. There are really two parts. The lens and a cell. The latter
looks like it has quite a bit of copper in it. Both are very heavy.


1" thick seems a bit on the thin side for a 20" lens element. What sort of
glass is it? Do you know the refractive index even?

Klazmon.

"Llanzlan Klazmon the 15th" wrote in message
7.6...
"W. Watson" wrote in
:

Our small science museum recently received in a very roundabout way a
20" dia. clear lens blank. It's about 1" thick and is in good shape.
We'd like to give it to someone who can use it in the Sacramento, CA or
Reno, NV that can put it to a legitimate astro use. If not, then perhaps
we could sell it and use the funds for the museum's astro fund. I have
no idea what it's worth, but perhaps there's some way to find out? I can
provide pix. There are really two parts. The lens and a cell. The latter
looks like it has quite a bit of copper in it. Both are very heavy.


1" thick seems a bit on the thin side for a 20" lens element. What sort of
glass is it? Do you know the refractive index even?

Klazmon.


I bet its a mirror blank, not a lens blank.

"Peter Webb" wrote in message
...

"Llanzlan Klazmon the 15th" wrote in message
7.6...
"W. Watson" wrote in
:

Our small science museum recently received in a very roundabout way a
20" dia. clear lens blank. It's about 1" thick and is in good shape.
We'd like to give it to someone who can use it in the Sacramento, CA
or
Reno, NV that can put it to a legitimate astro use. If not, then
perhaps
we could sell it and use the funds for the museum's astro fund. I have
no idea what it's worth, but perhaps there's some way to find out? I
can
provide pix. There are really two parts. The lens and a cell. The
latter
looks like it has quite a bit of copper in it. Both are very heavy.


1" thick seems a bit on the thin side for a 20" lens element. What sort
of
glass is it? Do you know the refractive index even?

Klazmon.


I bet its a mirror blank, not a lens blank.
Even then, 1" on a 20" mirror, would require a really superb multi-point
mirror cell. However I agree 'much more likely'.

Best Wishes

Roger Hamlett wrote:
"Peter Webb" wrote in message
...

"Llanzlan Klazmon the 15th" wrote in message
.37.6...

"W. Watson" wrote in
. net:


Our small science museum recently received in a very roundabout way a
20" dia. clear lens blank. It's about 1" thick and is in good shape.
We'd like to give it to someone who can use it in the Sacramento, CA
or
Reno, NV that can put it to a legitimate astro use. If not, then
perhaps
we could sell it and use the funds for the museum's astro fund. I have
no idea what it's worth, but perhaps there's some way to find out? I
can
provide pix. There are really two parts. The lens and a cell. The
latter
looks like it has quite a bit of copper in it. Both are very heavy.


1" thick seems a bit on the thin side for a 20" lens element. What sort
of
glass is it? Do you know the refractive index even?

Klazmon.


I bet its a mirror blank, not a lens blank.

Even then, 1" on a 20" mirror, would require a really superb multi-point
mirror cell. However I agree 'much more likely'.

Best Wishes


Sound like it is an optical window
d.

On Mar 14, 2:57 pm, "Roger Hamlett"
wrote:
"Peter Webb" wrote in message

...

"Llanzlan Klazmon the 15th" wrote in message
. 37.6...
"W. Watson" wrote in
et:

Our small science museum recently received in a very roundabout way a
20" dia. clear lens blank. It's about 1" thick and is in good shape.
We'd like to give it to someone who can use it in the Sacramento, CA

1" thick seems a bit on the thin side for a 20" lens element. What sort
of
glass is it? Do you know the refractive index even?

I bet its a mirror blank, not a lens blank.

If it is truly clear it may be intended as an optical flat window.

Even then, 1" on a 20" mirror, would require a really superb multi-point
mirror cell. However I agree 'much more likely'.

Grubb Parson experimented briefly with a technique where a relatively
thin mirror and tool were worked and then the mirror was carefully
grafted onto the back of the tool. The only surviving example I know
of is an 18" Naysmith design that due to lost bits is operated as a
Newtonian but there have always been rumours of a twin with location
unknown.

However, mirror blanks were rigged for best thermal expansion
properties and tended to have a green impure glass cast rather than
the water clear glass that would form a lens blank. Very expensive to
get rid of the colour impurities in glass so I guess it was intended
to transmit light. A photo may be worth a thousand word here.

ISTR The mirror cell of the 18" Grubb Design was a bronze casting and
not copper which is too soft.

Regards,
Martin Brown

I wish I knew. I may find out eventually. Someone identified the donor.

Llanzlan Klazmon the 15th wrote:
"W. Watson" wrote in
:

Our small science museum recently received in a very roundabout way a
20" dia. clear lens blank. It's about 1" thick and is in good shape.
We'd like to give it to someone who can use it in the Sacramento, CA or
Reno, NV that can put it to a legitimate astro use. If not, then perhaps
we could sell it and use the funds for the museum's astro fund. I have
no idea what it's worth, but perhaps there's some way to find out? I can
provide pix. There are really two parts. The lens and a cell. The latter
looks like it has quite a bit of copper in it. Both are very heavy.


1" thick seems a bit on the thin side for a 20" lens element. What sort of
glass is it? Do you know the refractive index even?

Klazmon.


--
Wayne Watson (Nevada City, CA)

Web Page: home.earthlink.net/~mtnviews