electronic telescope primary mirror

[Jamie Morken]

Hi all,

Would it be possible to substitute a 2d CCD array for the 3d parabola
mirror in a telescope if each CCD pixel only grabbed light with a phase
delay proportional to its "virtual" position on a parabolic mirror?


__ __
''-_ __-''
'-__ _--' virtual primary mirror
''-_ _--''
'''
--------------------------------- CCD array

(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)

So if a pixel in the CCD array was 1meter away vertically from the
virtual mirror, you would delay sampling the pixel about 3 nanoseconds
(approximate time it takes light to travel 1meter) compared to the pixel
at the root of the parabola, and you would sample the pixels at a rate
proportional to the frequency of the light you are receiving. I think
the light would also have to be polarized so that it is only travelling
vertically to the CCD. Also the CCD array would have to be custom in
that each pixel would have to be able to be triggered seperately and
very quickly.

I have always wanted to be able to build a telescope using just a planar
sheet of material and avoid having to have a precision mirror so this is
just a wild idea about that!

cheers,
Jamie

 

[PaulCsouls]

I don't think you understand how a lense works. You would get the same
image with a parabolic array of CCDs as you would with a flat array.
With a flat array you need a lense to image onto the array. With a
parabolic CCD array you would need a different kind of lense to image
onto the array. You can image onto a CCD using a pinhole lense. The
pinhole breaks up the image into little pieces putting a different
piece of the image onto different pixels of the CCD by the
relationship of the angle of the object to the pin hole and the CCD.
Just imagine looking through a pinhole and by moving your head around.
As you move your head you glimpse a little different piece of the
scene on the other side of the pin hole. If you move your head around
real fast the little piece will combine and you will see the whole
scene. With a mirror or lense the entire scene ends up on every spot
of the lense. What happens to create an image is that the light is
bent in such a way as to create an interference pattern that generates
the image. With a device as you describe you would only get a blur. No
interference pattern; no image.

Paul C

On Thu, 27 Jan 2005 11:24:28 GMT, Jamie Morken <jmorken@shaw.ca>
wrote:

Hi all,

Would it be possible to substitute a 2d CCD array for the 3d parabola
mirror in a telescope if each CCD pixel only grabbed light with a phase
delay proportional to its "virtual" position on a parabolic mirror?


__ __
''-_ __-''
'-__ _--' virtual primary mirror
''-_ _--''
'''
--------------------------------- CCD array

(created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)

So if a pixel in the CCD array was 1meter away vertically from the
virtual mirror, you would delay sampling the pixel about 3 nanoseconds
(approximate time it takes light to travel 1meter) compared to the pixel
at the root of the parabola, and you would sample the pixels at a rate
proportional to the frequency of the light you are receiving. I think
the light would also have to be polarized so that it is only travelling
vertically to the CCD. Also the CCD array would have to be custom in
that each pixel would have to be able to be triggered seperately and
very quickly.

I have always wanted to be able to build a telescope using just a planar
sheet of material and avoid having to have a precision mirror so this is
just a wild idea about that!

cheers,
Jamie

 

[Rich Grise]

On Fri, 28 Jan 2005 11:51:34 +0100, Rene Tschaggelar wrote:

Rich Grise wrote:

On Fri, 28 Jan 2005 03:34:03 +0000, Yukio wrote:


Did you know that the Hubble mirror could have been QC inspected and
tested with only a Pin-hole Light source and a Knife-edge. Idea was
overruled as too primitive, like building the Panama Canel with a pick
and shovel.!


Do you have links to any more information about this, or is it just more
UL?

Rich,
Telescopes can be tested against a point source. In earlier
times one used aluminum foil with a pinhole in front of a
lamp, nowadays, I'd rather use a laserdiode without optics
in 500m distance. The 10um in square are pretty close to a
point soutce. Through the telescope one then sees the bessel
rings of the fourier transformed point source if the telescope
is right. Otherwise one sees the distortions in interferometry
style.

Ah. Thanks for this. All I could think of was, "point source, pinhole -

doesn't that mean "spherical?"

Forgot all about those rings.

Thanks!
Rich