LBT achieves higher resolution than Hubble ST

[crazyeddie]

This is a very exciting development, and bodes well for ground-based astronomy:


The next generation of adaptive optics has arrived at the Large Binocular Telescope (LBT) in Arizona, providing astronomers with a new level of image sharpness never before seen. Developed in a collaboration between Italy's Arcetri Observatory of the Istituto Nazionale di Astrofisica (INAF) and the University of Arizona's Steward Observatory, this technology represents a remarkable step forward for astronomy. The LBT, with its two 8.4 metre -mirrors, is the largest optical telescope in the world.

The $120 million LBT on Mount Graham utilizes two giant 8.4 metre mirrors and with the new adaptive optics the telescope will achieve the resolution of a 22.8-metre, or approximately 75-foot telescope. Implementation of the adaptive optics is the latest of several major breakthroughs for the LBT in recent months. For example, in April 2010, a near-infrared camera/spectrograph developed by a consortium of German institutes became available to astronomers for scientific observations, allowing them to penetrate interstellar dust clouds and reveal the secrets of the youngest and most distant galaxies. The new adaptive optics will enable other such versatile instruments to achieve their full potential on the LBT.

Until recently, ground-based telescopes had to live with wavefront distortion caused by the Earth's atmosphere which significantly blurred images of distant objects (this is why stars appear to twinkle to the human eye). While there have been advancements in adaptive optics technology to correct atmospheric blurring, the LBT's innovative system truly takes this concept to a whole new level.

In closed-dome tests beginning May 12 and sky tests every night since May 25, astronomer Simone Esposito and his INAF team tested the new device, achieving exceptional results. The LBT's adaptive optics system, called the First Light Adaptive Optics system (FLAO), immediately outperformed all other comparable systems, delivering an image quality greater than three times sharper than the Hubble Space Telescope using just one of the LBT's two 8.4 metre mirrors. As soon as the adaptive optics are in place for both mirrors and their light is combined appropriately, it is expected that the LBT will achieve image sharpness ten times that of the Hubble.

http://www.astromart.com/news/news.asp?news_id=1084

 

[aphh]

Is the image text in the article 0.16 arc seconds for the separation of the two stars? This baby is going to see things. If the moon was 0.5 degrees wide on average, resolution of 0.1 arcseconds would be equivalent of roughly 200 meters on the moon.

This scope could eventually see what is, and what was, going on on the surface of the moon.

 

[ravnostic]

Nice. Stuff like this will make Hubble and other space telescopes completely unnecessary, at least at visual wavelengths.

 

[James_Bull]

Sweet!! Does that mean the 42m European Extremely freakin big and ridiculously Large Telescope (EELT for short i think) will be able to achieve a resolution of roughly 100m with the moon?

 

[aphh]

Sweet!! Does that mean the 42m European Extremely freakin big and ridiculously Large Telescope (EELT for short i think) will be able to achieve a resolution of roughly 100m with the moon?

Doubling the diameter of the mirror increases the light-gathering area and thus potential resolution four times. For Earth based telescope a lot depends on the adaptive optics, and they seem to have mastered that with LBT.

Once the second mirror come on-line, that should double the resolution (in theory, atleast). But having two eyes instead of just one has an added benefit, instead of pointing the mirrors to the exact same direction, they will look slightly cross-eyed. This improves the resolution even further, the technology is called sub-pixel rendering.

If with just one eye your limiting resolution was 1 pixel, having two eyes with both having limiting resolution of 1 gives the resolution of 0.5 pixels when combined properly. The other eye would see the bottom of the pixel and the other would see the top of the pixel.

 

[MeteorWayne]

Sweet!! Does that mean the 42m European Extremely freakin big and ridiculously Large Telescope (EELT for short i think) will be able to achieve a resolution of roughly 100m with the moon?

Doubling the diameter of the mirror increases the light-gathering area and thus potential resolution four times. For Earth based telescope a lot depends on the adaptive optics, and they seem to have mastered that with LBT.

Once the second mirror come on-line, that should double the resolution (in theory, atleast). But having two eyes instead of just one has an added benefit, instead of pointing the mirrors to the exact same direction, they will look slightly cross-eyed. This improves the resolution even further, the technology is called sub-pixel rendering.

If with just one eye your limiting resolution was 1 pixel, having two eyes with both having limiting resolution of 1 gives the resolution of 0.5 pixels when combined properly. The other eye would see the bottom of the pixel and the other would see the top of the pixel.

Wrong. Doubling the mirror size increases the light gathering ability by 4, but only increases the resolution by 2.
Basic physics, my friend.

 

[aphh]

Wrong. Doubling the mirror size increases the light gathering ability by 4, but only increases the resolution by 2. Basic physics, my friend.

You did not specify whether you meant optical resolution or perceived resolution. Neither did I. These are both same and different things. To me the ability to see four times fainter objects is an increase in perceived resolution.

You could have a scope with twice the optical resolution and half the light gathering ability and a scope with half the optical resolution but twice the light gathering ability.

Both would have the same perceived resolution, but they would see different things. The other could not see the fainter objects and the other could not see the smaller objects.

There's more to it, but you get the point.

 

[MeteorWayne]

Wrong. Doubling the mirror size increases the light gathering ability by 4, but only increases the resolution by 2. Basic physics, my friend.

You did not specify whether you meant optical resolution or perceived resolution. Neither did I. These are both same and different things. To me the ability to see four times fainter objects is an increase in perceived resolution.

That's pure obfuscating balony.

You need to learn that in science specific words have specific meanings. You can't just keep making up new ones as you go along to support your point.

 

[aphh]

That's pure obfuscating balony.

You need to learn that in science specific words have specific meanings. You can't just keep making up new ones as you go along to support your point.

Okay, here is what I wrote originally: "Doubling the diameter of the mirror increases the light-gathering area and thus potential resolution four times."

There is no mention of optical resolution at all. There is a mention of potential resolution. Anybody can open up a wikipedia page and have a look at the formula for optical resolution. But it is just one part of the whole concept.

The ability to see dimmer objects is another. Then there is the shape of the mirror and how accurate that is. These all add up and you finally get the practical resolution, which can only be determined by tests. Hence the word "potential".

Learn to think conceptual. Don't be stubborn booksmart.

 

[MeteorWayne]

Learn to use the words of scince correctly.

 

[csmyth3025]

Learn to use the words of scince correctly.

In my quest to learn more obfuscating science baloney (or bologna, if you prefer), when you double the size of your telescope (lens or mirror) you increase the light gathering capacity 4 times. This makes sense to me because A=pi*r^2.

I found the following in the Wikipedia article on optical telescopes:

Ignoring blurring of the image by turbulence in the atmosphere (atmospheric seeing) and optical imperfections of the telescope, the angular resolution of an optical telescope is determined by the diameter of the objective, termed its "aperture" (the primary mirror, or lens.) The Rayleigh criterion for the resolution limit αR (in radians) is given by:

a_R=1.22(lambda/D)

where λ is the wavelength and D is the aperture. For visible light (λ = 550 nm) in the small-angle approximation, this equation can be rewritten:

a_R=138/D

Here, αR denotes the resolution limit in arcseconds and D is in millimeters. In the ideal case, the two components of a double star system can be discerned even if separated by slightly less than αR. This is taken into account by the Dawes limit:

a_D=116/D

The equation shows that, all else being equal, the larger the aperture, the better the angular resolution.

I don't pretend to understand how these formulas are derived, but they do seem to show that the arcsecond resolution is inversely proportional to the size of the aperture. That is, if the aperture is twice as big, the arcsecond resolution is halved.

I'm guessing that this is why doubling the size of your lens (or mirror) increases the light gathering capacity of your telescope 4 times but only doubles the resolution of your telescope. You can see fainter things (4 times fainter?) but you can only discern separate things that are separated by 1/2 the angular separation. Is this approximately right?

PS I'm not halfway through any degree programs so my feelings wont get hurt if you tell me I'm full of bologna.

Chris

 

[MeteorWayne]

You've got it right csmyth

 

[James_Bull]

So.... I was right! Thanks guys

 

[JonClarke]

Nice. Stuff like this will make Hubble and other space telescopes completely unnecessary, at least at visual wavelengths.

Not at all

Space telescopes in visual wavelenghts can still collect much longer exposures, can take images at any time of day or night, are not effected by weather or light pollution.

 

[aphh]

I'm guessing that this is why doubling the size of your lens (or mirror) increases the light gathering capacity of your telescope 4 times but only doubles the resolution of your telescope. You can see fainter things (4 times fainter?) but you can only discern separate things that are separated by 1/2 the angular separation. Is this approximately right?

It is, but as mentioned before, the genius of LBT is having two eyes, instead of just one. The mirrors will work in tandem as an interferometer. Hence by doubling the diameter by having two mirrors, you now actually have the potential to get four times the resolution or 1/4 of the angular resolution in radians.

This is because you can adjust the mirrors so that the other mirror sees half wavelength different image. When the images are combined, the resolution is doubled. Think of it like having the resolution of five fingers of your right hand. When you combine with your left hand and cross your fingers, you have the combined resolution of ten fingers.

Hence what we have here is A) doubling the diameter with the second mirror (doubles resolution) and B) half-wave resolution of one mirror (again doubles potential resolution).

So there is potential for four times the angular resolution for LBT, when the other eye comes on-line.

 

[MeteorWayne]

aphh, I just love how you make stuff up with no respect for reality and expect people to believe it.

 

[aphh]

aphh, I just love how you make stuff up with no respect for reality and expect people to believe it.

I am sorry if you struggle even with simple concepts, but once again, Modulation Transfer Function Limit is easy to understand and logical too.

Get the basics from here: http://photo.net/learn/optics/mtf/
Especially scroll the page a bit and there is a graph of comparison of a perfect F4 lens and a similar F4 lens with 1/2 wave error. Note also, that no perfect or ideal lens or mirror exists in reality, so two less-than-ideal lenses or mirrors when correctly focused will increase the MTFL.

This is simple physics of wavefronts and constructive interference.

Basically you have a lens or mirror that can see black and white stripes or dots (modulation) with certain minimum width. When you exceed the MTF limit, the black and white is mixed and seen as grey. No more modulation.

But having two separate lenses or mirrors allows the other one to concentrate on the black dots and the other one sees the white dots so that they aren't mixed into grey. Once you combine the images, you will have twice the resolution of just one lens or mirror.

This is actually a simple concept, but I don't think it has been done even close to LBT scale before.

Edit: I even have a very practical example of this, I am in need of new glasses. When I look at text on the wall with the other eye closed, the text is less readable and clear than when looked at with both eyes. This is exactly the very phenomenon of what the LBT should benefit from. Two eyes are better than one.

 

[aphh]

Any info on how the second eye is coming on-line? I know I could do the research also, but asking here first.

 

[Astro_Robert]

A couple of things.

I heartedly agree with JonClarke about space telescopes. However, this adaptive optics advance is a huge deal, and probably will have an effect on what type of science is bid for on the Hubble, given that ground based telescopes will now be able to handle more of that science. Also note that certain wavelengths (UV, Xray, etc..) are heavily absorbed by the atmosphere and can only be done from extremely high altitude or orbit.

The whole arguement on telescope "power" vs size is a litle missleading in this case. For a normal telescope when you double the diameter, then the area of a circle goes up by 4, due to A = Pi * R^2. If the radius doubles then the area goes up by 4. However, in this case we simply have 2 lenses of the same size, so light gathering power is merely double that of a single 8.4m telescope.

Also most of the nice equations cited pertain to telescopes with a single primary lens/mirror. Being a binocular, the resolution on this telescope is related to the separation of the scopes and not just to the point that there are two of them.

So, LBT is using adaptive optics to approach very close to what a space based telescope of the same size could do resolution wise (of course it is much larger than Hubble is, and not expensively engineered to make it into orbit). Once LBT brings the second mirror online as an Interferometer it will doulbe its light gathering power and increase its resolution. You can check on the LBT homepgae, they indicate an operation optical baseline of 23m due to the separation of the primaries.

It is exciting and hopefully they can hold to their schedule. The homepage also notes an expected Interferometer functional date of 2011 depending on when adaptive optics is available on both primary mirrors.

http://lbti.as.arizona.edu/LBTI-Main/Telescope.html

 

[Astro_Robert]

Two eyes are not always better than one.

Eyes can have different focus levels on them, causing people to use one or the other eye for a given task. In fact, it is not unusual for people getting laser eye surgery to get one eye optimized for distance vision (driving) and the other eye optimized for close up vision (reading).

This is done because as a person ages, the eye lens is no longer as flexible at deforming for different focal lengths, so the eye doctors can help ensure a person is able to function in any given situation by having at least one eye properly in focus for either a distant or nearby event.

 

[ZenGalacticore]

Two eyes are not always better than one.

Eyes can have different focus levels on them, causing people to use one or the other eye for a given task. In fact, it is not unusual for people getting laser eye surgery to get one eye optimized for distance vision (driving) and the other eye optimized for close up vision (reading).

This is done because as a person ages, the eye lens is no longer as flexible at deforming for different focal lengths, so the eye doctors can help ensure a person is able to function in any given situation by having at least one eye properly in focus for either a distant or nearby event.

Interesting. Glad to see you back in these parts, Astro Robert!

 

[aphh]

Two eyes are not always better than one.

Eyes can have different focus levels on them, causing people to use one or the other eye for a given task. In fact, it is not unusual for people getting laser eye surgery to get one eye optimized for distance vision (driving) and the other eye optimized for close up vision (reading).

This is done because as a person ages, the eye lens is no longer as flexible at deforming for different focal lengths, so the eye doctors can help ensure a person is able to function in any given situation by having at least one eye properly in focus for either a distant or nearby event.

If I may disagree slightly... I think you just gave us a case where two eyes are better than one?