Apollo moon hoaxers take a look at this:

Originally posted by twhitehead
I am afraid I do not follow your logic at all. With a standard handheld digital camera, the formula for resolution includes lens size, zoom, sensitivity, exposure etc. I do not believe that resolution is ever limited by lens size. A cell phone camera with a 1mm can potentially take as good a picture as a camera with a 20mm lens if the zoom and sensitivity ...[text shortened]... telescope is that the zoom is determined by the curvature of the dish, not the size of the dish.

I assume by zoom you mean the magnification? Take a look at this and look at the section 'lens resolution'.

http://en.wikipedia.org/wiki/Optical_resolution

If you have an earth bound telescope, say a nice Celestron, you get some eye piece lenses. You can use say a 25 mm eyepiece and get say 30 power of magnification.

If you use a 12.5 mm eyepiece you get 60 power

A 6 mm gets you about 120 power.

3 mm gets you 240 power.

1.5 mm gets you 480 power.

0.75 gets you close to 1000 power.

There are a couple of problems with that situation.

One is the size of the image gets smaller as they eyepiece gets smaller, you get greater magnification but the image size gets smaller than your pupil so you see smaller and smaller circles with the image in them.

The second is diffraction limit of the lens or mirror. Sin Theta=1.22 * (wavelength of light/diameter of the lens)

Sin theta is the diffraction limit. Notice as the size of the lens gets smaller, the diffraction limit gets bigger.

So in order to get better diffraction limits you need bigger lenses. Doesn't matter how many pixels your sensor has, once you reach diffraction limit you can't get any more magnification.

If we could achieve great resolution with a 1 mm lens, why would we build telescopes with 2 meter, 10 meter, 20 meter diameter mirrors? There are fundamental limits we cannot at this point in our technological development, go beyond in terms of resolution Vs lens size.

There are in development a property of lenses called negative refraction index and that may allow lenses that surpass the so far fundamental resolution Vs size limitations but not yet at least for telescopes. There is work going on to get around the limits of optical microscopes with negative refractive indexes and such but I don't think a commercial product is out yet in that field.

Here is a brief layman article about negative refractive index material:

http://www.economist.com/node/417791

Originally posted by sonhouse
The second is diffraction limit of the lens or mirror. Sin Theta=1.22 * (wavelength of light/diameter of the lens)

Does that apply to mirrors? I don't think it does, but I could be wrong.

If we could achieve great resolution with a 1 mm lens, why would we build telescopes with 2 meter, 10 meter, 20 meter diameter mirrors?
Its also about light gathering capacity, and atmospheric interference and the fact that it is easier to get a large lens/mirror accurate than a small one.

There are fundamental limits we cannot at this point in our technological development, go beyond in terms of resolution Vs lens size.
I agree, but I don't believe lens size is everything. I don't think the fundamental limits are any where near met when it comes to satellite telescopes. Again, I may be wrong.

Originally posted by twhitehead
Does that apply to mirrors? I don't think it does, but I could be wrong.

[b]If we could achieve great resolution with a 1 mm lens, why would we build telescopes with 2 meter, 10 meter, 20 meter diameter mirrors?
Its also about light gathering capacity, and atmospheric interference and the fact that it is easier to get a large lens/mirror accurate l limits are any where near met when it comes to satellite telescopes. Again, I may be wrong.[/b]

Mirrors and convex lenses do the same exact job but in a different way. They both bring light to a focal point and have exactly the same problem with diffraction limits.

And you are partially right about the size of the lens/mirror, larger size means more light gathered so a job done on a large scope can be done in a shorter amount of time and it will have better resolution than a smaller one.

Didn't you see the formula I gave? That is fundamental, large lens/mirror = smaller diffraction limit, small lens=larger diffraction limit which means less resolution. It's pretty cut and dried.

Originally posted by sonhouse
Mirrors and convex lenses do the same exact job but in a different way. They both bring light to a focal point and have exactly the same problem with diffraction limits.

Do you have any references for this? I thought mirrors didn't diffract light.

Originally posted by twhitehead
Do you have any references for this? I thought mirrors didn't diffract light.

references, still trying to get others to do your research you lazy bum, even when you
are provided with references you dispute them or fail to understand them, there is no
point in engaging with you in any capacity whatsoever, other than to say,


[CENSORED: This post has been removed to preserve sanity levels]

Originally posted by twhitehead
Do you have any references for this? I thought mirrors didn't diffract light.

http://en.wikipedia.org/wiki/Diffraction-limited_system

You are defining diffraction in a different way than the meaning in optics. I think you are thinking of diffraction of light on regular surfaces like say a layer of sand which reflects light in all different directions and diffracting light also.

The definition of diffraction in optics is what the focused spot looks like. The spot of light say from a perfectly parallel wavefront of light impinging on a lens produces a spot of light but it is not a perfect spot, there is a diffraction of light around the spot in different sized rings. This article talks about that.

Here is another discussion of the issue with some graphics:

http://www.oldham-optical.co.uk/Airy%20Disk.htm

Originally posted by sonhouse
You are defining diffraction in a different way than the meaning in optics. I think you are thinking of diffraction of light on regular surfaces like say a layer of sand which reflects light in all different directions and diffracting light also.

The definition of diffraction in optics is what the focused spot looks like. The spot of light say from a per ...[text shortened]... a diffraction of light around the spot in different sized rings. This article talks about that.

I thought 'diffraction' simply meant 'bending', but it seems it refers rather to the interference pattern resulting when waves are bent different amounts by an object.
I also thought this did not occur with mirrors, and again, it seems I was mistaken.

Thanks for the references.

Originally posted by twhitehead
I thought 'diffraction' simply meant 'bending', but it seems it refers rather to the interference pattern resulting when waves are bent different amounts by an object.
I also thought this did not occur with mirrors, and again, it seems I was mistaken.

Thanks for the references.

I was thinking about that airy disk thing and was wondering if the application of a plug on the edge of the mirror that absorbed all the light or as close to 100% as possible and use a thinning edge down to the actual mirror so it doesn't present an edge, just a gradual transition, wonder if that could help make the airy disk smaller? Like those nanocrystals that I read about recently that absorbs almost all the light in sees.

Originally posted by sonhouse
I was thinking about that airy disk thing and was wondering if the application of a plug on the edge of the mirror that absorbed all the light or as close to 100% as possible and use a thinning edge down to the actual mirror so it doesn't present an edge, just a gradual transition, wonder if that could help make the airy disk smaller? Like those nanocrystals that I read about recently that absorbs almost all the light in sees.

I don't think the airy disk has anything to do with the mirrors edges. It has to do with the fact that not all the light reflecting off the mirror reflects at the perfect angle. Some reflects at slightly greater or slightly smaller angles resulting in an interference pattern. This happens at every point on the mirror and the airy disk exists around every point on the image (but is only obvious where there are bright points on dark eg stars elsewhere it just results in a decrease in resolution).

But I am still not convinced that this is the current limit for most telescopes. Wikipedia clearly says that atmospheric distortion is the main limiting factor for earth bound telescopes, and Hubble originally suffered from a distorted mirror. The fact that long exposures can result in better images, suggests that sensitivity of the sensors is now one of the main factors.

Originally posted by twhitehead
I don't think the airy disk has anything to do with the mirrors edges. It has to do with the fact that not all the light reflecting off the mirror reflects at the perfect angle. Some reflects at slightly greater or slightly smaller angles resulting in an interference pattern. This happens at every point on the mirror and the airy disk exists around every ...[text shortened]... sult in better images, suggests that sensitivity of the sensors is now one of the main factors.

It does not have to do with imperfections in the mirror. You seem to refuse to accept what has already been explained. They can test the validity of the parabolic curve with extreme accuracy and if you look at the specs for telescopes, the mirrors are rated in terms of light wavelengths. Green light has a wavelength of roughly 1/25,000 of an inch. The worse ratings on scopes is in the area of 1/8th wavelength, or 1/10th wavelength. That is accuracy within 1/250,000th of an inch and some are figured to within 1/20th of a wavelength, about 2 MILLIONTHS of an inch accuracy. That means that all the waves arrive on target within 5 percent of a wavelength apart, way too low by itself to have caused the airy disk. That is not the issue.

Now btw, there is an entirely new technology being used on some of the largest scopes on the planet, deformable mirrors.

What they do is to shoot a powerful laser into the sky in the path that the scope would be looking at, that illuminates a patch of atmosphere about 20 to 50 miles up. The scope itself gets the return image of the dot in the atmosphere which, because of atmospheric distortions, the scope sees the laser dot wiggle around because of the diffraction effects of the moving atmosphere. A computer controls the mirror, causing very small changes in the shape of the surface and the net result is to make the laser dot stand still in the image center.

Using that then, they compensate for 99 percent of the distortion caused by the atmosphere so now the big scopes can get better resolution than the Hubble. More accurately, they can better utilize the inherently better resolution of the much larger mirrors which very accurately brings the light to a single point with a much smaller airy disk.

You are also wrong about the long term exposure thing. When the Hubble took a long term exposure of a patch of sky with not many stars in it, hours and hours of looking at the same exact patch of sky, there was zero increase in resolution but a big increase in the number of weak light sources because all the sensor outputs are integrated together digitally where the signals add up and the weak sources are now visible. It had the resolution all along to see such weak sources but it did not collect enough photons to make out the sources.

Remember, for the weakest sources, those galaxies and quasars 10 and 12 billion light years away, only a few photons reach the scope at any one time and it takes a certain amount of photons to get an image.

So a photon comes in, gets counted and the position noted. Then a few minutes later, another single photon from that source comes in, gets counted, the position is a bit different so it came from a different part of the galaxy and its new position is noted.

So after hours of doing this, an image is slowly built up and hundreds of galaxies are images that were never seen before.

The newest generation of land based scopes can do that same job and get even better resolution because the mirrors are a heck of a lot bigger so they intercept more photons at a given time so get the same image in a much shorter period of time.

Hubble and other space born telescopes still beat out Earth based ones because the atmosphere blocks off the edges of the bandwidth a scope can be sensitive to, the IR band and the UV bands. Since no light or very little light from those bands ever make it to Earth, the ones in space still get and will forever get, better images in those bands and they add to the knowledge of the total of astronomy.

So there are jobs Earth based telescopes cannot do in spite of the fact that 21st century technology can eliminate the wiggle introduced to starlight introduced by the atmosphere.

Originally posted by sonhouse
It does not have to do with imperfections in the mirror. You seem to refuse to accept what has already been explained.

Actually no, I said nothing about imperfections in the mirror. It seems that a perfect mirror still has some diffraction whereby some light does not reflect at the perfect angle. I think it has something to do with quantum mechanics and the wave nature of light. My point is that it has nothing to do with the edge of the mirror (which is what I thought you suggested was causing it).

You are also wrong about the long term exposure thing. When the Hubble took a long term exposure of a patch of sky with not many stars in it, hours and hours of looking at the same exact patch of sky, there was zero increase in resolution but a big increase in the number of weak light sources because all the sensor outputs are integrated together digitally where the signals add up and the weak sources are now visible. It had the resolution all along to see such weak sources but it did not collect enough photons to make out the sources.
I think I get that now. Thanks.

Originally posted by twhitehead
Actually no, I said nothing about imperfections in the mirror. It seems that a perfect mirror still has some diffraction whereby some light does not reflect at the perfect angle. I think it has something to do with quantum mechanics and the wave nature of light. My point is that it has nothing to do with the edge of the mirror (which is what I thought you ...[text shortened]... it did not collect enough photons to make out the sources.
I think I get that now. Thanks.[/b]

There are of course quantum fluctuations in the surface of the mirror but they are big time orders of magnitude smaller than the wavelength of light. The quantum fluctuations would think those light waves we view which at 1/25,000 of an inch, would be like us looking at radio waves the size of the solar system, that is to say, just as an example, a radio wave with a wavelength of say, 10 billion miles or about 1/53,000 ths of a hertz.

You get what I am getting at here? So that 10 billion mile wide wavelength hits a reflector of some kind, say a 50 billion mile wide mirror, the quantum fluctuations would be still smaller and have practically no effect on any scattering of the waves.

I don't even know if there IS such a thing as an RF wave of that size, where it would take 50,000 seconds to go by, just making an analogy.

I have done some arm chair calculations of waves almost that big going by the sun and how they would be effected by the gravitational lens the sun makes but I only thought about waves a million miles long or so, 1/5th of a hertz or so.

The gist of it is, quantum fluctuations are way smaller than anything a molecule could see, for instance, in order to work with quantum fluctuations and such, the temperature usually has to be near absolute zero, minus 273 degrees C.

As it stands now for room temperature mirrors, the random dance of molecules due to heat way overwhelms quantum effects.

It seems the rings of the airy disks really are from the edge of the mirror.

Any kind of discontinuity can make extended rings around the airy disk.

Didn't you look at the last link I gave you? It shows the effect with graphics.

Originally posted by sonhouse
There are of course quantum fluctuations in the surface of the mirror but they are big time orders of magnitude smaller than the wavelength of light.

You are misunderstanding me (probably my fault).
I am not saying the surface fluctuates due to quantum mechanics. I am saying that light does not, ever, reflect perfectly due to quantum mechanics. (light can be considered a wave because of quantum mechanics). The Airy disc is essentially a direct result of the wave nature of light.

But my point is that the pattern has nothing whatsoever to do with the edge of the mirror, it is a result of interference between light waves reflecting off all parts of the mirrors surface.

Didn't you look at the last link I gave you? It shows the effect with graphics.
Yes, and I think he has got it wrong (and even admits it)

This is where I “cop out” and say this is due to the wave nature of light and you do need to start digging into the physics text books if you want to understand it better.

Originally posted by twhitehead
You are misunderstanding me (probably my fault).
I am not saying the surface fluctuates due to quantum mechanics. I am saying that light does not, ever, reflect perfectly due to quantum mechanics. (light can be considered a wave because of quantum mechanics). The Airy disc is essentially a direct result of the wave nature of light.

But my point is tha need to start digging into the physics text books if you want to understand it better.[/quote]

Well you are making assertions without experimental backup. There is a lot of theory about photons which come in all wavelengths from those measured in hundreds of meters to those measured in angstroms.

If you have a theory about that you need to do experiments or something not just make assertions based on a hunch.

I am not sure which one you said he admits something he doesn't know, here is the link again, look at this one:

http://www.oldham-optical.co.uk/Airy%20Disk.htm

Originally posted by sonhouse
Well you are making assertions without experimental backup. There is a lot of theory about photons which come in all wavelengths from those measured in hundreds of meters to those measured in angstroms.

If you have a theory about that you need to do experiments or something not just make assertions based on a hunch.

This is not about me doing new science (or claiming a new discovery). Rather it is about my understanding of the currently accepted explanation for Airy rings as described on Wikipedia.
Maybe my understanding is completely wrong.