A wacky telescope making idea...

Aside from the fact that the requirements for focusing radio waves is less
than the requirements to focus light waves . . .

A group of flat surfaces does not focus light to a point, which is needed
if you're going to get anything close to a clear view. The segmented
mirrors used in the Keck and other scopes are themselves parabolic, so each
can focus the light without the need of the other mirrors. CDs, even if
reflective enough, are not curved in parabolas, hence none of them will
bring the light to a focus, and hence the entire setup won't come to any
focus, hence no images. Hence no telescope.
--
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There is a fifth dimension beyond that which is known to Man.
It is a dimension as vast as space and as timeless as infinity.
It is the middle ground between light and shadow,
Between Science and superstition
And it lies between the pit of Man's fears
and the Sunlight of his knowledge.
It is the dimension of imagination.
It is an area that might be called. . . The Twilight Zone.


----------------------------------------------------------------------

"jagbot" wrote in message
om...
Hello all:

I have no experience making telescopes. Advance apologies if this idea
is stupid and shouldnt have been posted at all. OTOH, I would like
some feedback. Please read on:

I look at a Sky TV dish and it seems parabolic. The radio/tv waves are
reflected off it and brought to focus at the reciever. To convert this
dish into a mirror, I assemble a large number of CDs that reflect
light decently, cut them up to small pieces and stick them along the
dish without leaving any gaps. I now have a parabolic mirror whose
radius is the radius of the dish with focal point at the reciever. I
replace the reciever with a secondary mirror and direct the light to a
focusser where an eyepiece can be fitted. Have I got a telescope?

Thank you.

radius is the radius of the dish with focal point at the reciever. I
replace the reciever with a secondary mirror and direct the light to a
focusser where an eyepiece can be fitted. Have I got a telescope?

Heavens, no. The required precision of the parabolic surface of a telescope
mirror is about 0.0001 millimeter. You will be off by many millimeters.
You will not get a viewable image.

Also, the parabola of a satellite dish is way too deep in proportion to its
diameter. Satellite dishes are about f/0.3 as I recollect. Even if it were
optically perfect, a parabolic mirror of this general size and shape would
not form a sharp image over an area more than about 1 mm in diameter.

What you propose would not work as a telescope, but it would work as a solar
furnace.


--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

radius is the radius of the dish with focal point at the reciever. I
replace the reciever with a secondary mirror and direct the light to a
focusser where an eyepiece can be fitted. Have I got a telescope?

Heavens, no. The required precision of the parabolic surface of a telescope
mirror is about 0.0001 millimeter. You will be off by many millimeters.
You will not get a viewable image.

Also, the parabola of a satellite dish is way too deep in proportion to its
diameter. Satellite dishes are about f/0.3 as I recollect. Even if it were
optically perfect, a parabolic mirror of this general size and shape would
not form a sharp image over an area more than about 1 mm in diameter.

What you propose would not work as a telescope, but it would work as a solar
furnace.


--
Clear skies,

Michael Covington -- www.covingtoninnovations.com
Author, Astrophotography for the Amateur
and (new) How to Use a Computerized Telescope

"Fleetie" wrote:

By the way, I'm bull****ting,

I'm sure the good Doctor will confirm that the charter lays down cruel
and unusual punishments for tautology...

Sorry Martin - couldn't resist.

I think these guys are onto something - henceforth all telescopes will
be made out of woks and collanders. My old 10 inch mirror will be dead
handy for making chips - while I gaze down into a lovely image of my
face - stomach and ego satisfied in one easy operation - irresistable.

-----------------------------
Martin Frey
http://www.hadastro.org.uk
N 51 01 52.2 E 0 47 21.1
-----------------------------

"Fleetie" wrote:

By the way, I'm bull****ting,

I'm sure the good Doctor will confirm that the charter lays down cruel
and unusual punishments for tautology...

Sorry Martin - couldn't resist.

I think these guys are onto something - henceforth all telescopes will
be made out of woks and collanders. My old 10 inch mirror will be dead
handy for making chips - while I gaze down into a lovely image of my
face - stomach and ego satisfied in one easy operation - irresistable.

-----------------------------
Martin Frey
http://www.hadastro.org.uk
N 51 01 52.2 E 0 47 21.1
-----------------------------

On Fri, 21 Nov 2003 01:48:22 +0000, Martin Frey
wrote:

...

I think these guys are onto something - henceforth all telescopes will
be made out of woks and collanders. My old 10 inch mirror will be dead
handy for making chips - while I gaze down into a lovely image of my
face - stomach and ego satisfied in one easy operation - irresistable.

-----------------------------
Martin Frey
http://www.hadastro.org.uk
N 51 01 52.2 E 0 47 21.1
-----------------------------


Don't underestimate the versatility of woks.. Just recently Stefan Raab, a
German talk show host has staged a sporting event where they went down a
bob run in woks..
So they had one-man wok and four-man wok instead of bobs..

Regards,

Joerg

--
Joerg Glissmann

remove pants to reply..

On Fri, 21 Nov 2003 01:48:22 +0000, Martin Frey
wrote:

...

I think these guys are onto something - henceforth all telescopes will
be made out of woks and collanders. My old 10 inch mirror will be dead
handy for making chips - while I gaze down into a lovely image of my
face - stomach and ego satisfied in one easy operation - irresistable.

-----------------------------
Martin Frey
http://www.hadastro.org.uk
N 51 01 52.2 E 0 47 21.1
-----------------------------


Don't underestimate the versatility of woks.. Just recently Stefan Raab, a
German talk show host has staged a sporting event where they went down a
bob run in woks..
So they had one-man wok and four-man wok instead of bobs..

Regards,

Joerg

--
Joerg Glissmann

remove pants to reply..

Martin Frey wrote in message . .

I think these guys are onto something - henceforth all telescopes will
be made out of woks and collanders. My old 10 inch mirror will be dead
handy for making chips - while I gaze down into a lovely image of my
face - stomach and ego satisfied in one easy operation - irresistable.

Martin Frey


Despite your (assumed) attempt at humour you are the only one in this
thread to hit the nail on the head. A solar heater for the odd cup of
tea might be possible if you polish the dish well and the Sun actually
was shining. I'd recommend the aluminium variety though, rather than
the pressed steel ones. Or simply cover the face with reflective
mylar/space blanket. Such a device is not uncommon, or new. Leonardo
is supposed to have came up with a "solar weapon". The idea being to
use a large dish to fry the enemy at sea. Or at least set fire to his
sails. But he was way ahead of his time as usual. As he didn't have
access to CDs the idea was a flop.

Chris.B

Martin Frey wrote in message . .

I think these guys are onto something - henceforth all telescopes will
be made out of woks and collanders. My old 10 inch mirror will be dead
handy for making chips - while I gaze down into a lovely image of my
face - stomach and ego satisfied in one easy operation - irresistable.

Martin Frey


Despite your (assumed) attempt at humour you are the only one in this
thread to hit the nail on the head. A solar heater for the odd cup of
tea might be possible if you polish the dish well and the Sun actually
was shining. I'd recommend the aluminium variety though, rather than
the pressed steel ones. Or simply cover the face with reflective
mylar/space blanket. Such a device is not uncommon, or new. Leonardo
is supposed to have came up with a "solar weapon". The idea being to
use a large dish to fry the enemy at sea. Or at least set fire to his
sails. But he was way ahead of his time as usual. As he didn't have
access to CDs the idea was a flop.

Chris.B

I had this idea of putting a 4.5-inch mirror into my CD player to see if it
plays. I'll probably need to drill a hole first...

Edwin.