Supersharp Images from New VLT Adaptive Optics • Hacker News Board

Re: Supersharp Images from New VLT Adaptive Optics

#21

Post by eisstrom » Wed, Jul 18, 2018, 12:49 PM UTC

vanderZwan wrote: post #14

eisstrom wrote: post #5

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

> With this new capability, the 8-metre UT4 reaches the theoretical limit of image sharpness and is no longer limited by atmospheric blur. Theoretical limit as in diffraction limited? How will this technology "scale" to other frequencies and resolutions? Related to this diffraction limit: is there any overlap in the advances in microscopy and astronomy? For example, do advances in super-resolution microscopy[0] affec…

Yes, the diffraction limit is meant here. The VLT has four 8 m mirrors, for each of them the angular resolution limit is = wavelength/diameter = 8 * 10^(-8) rad. The practical resolution of the new narrow-field mode is about 4*10^(-7) rad, and it was one order of magnitude larger before.

Adaptive optics is the key invention here. As far as I know, it works better in the near-infrared than in the red part of the optical range, and it gets worse toward the blue part. Due to this, our resolution changes as a function of the wavenlength, since MUSE captures the flux from all wavelengths at the same time.

ESO wants to achieve an even higher resolution at the 40m Extremely Large Telescope (another order of magnitude better): https://www.eso.org/public/teles-instr/elt/

It's funny that your mention super-resolution microscopy because Stefan Hell, one of the Nobel Prize winners for advances in that field, works in the same city as we do. So far, I don't think we have any overlap with what he does.

Re: Supersharp Images from New VLT Adaptive Optics

#22

Post by eisstrom » Wed, Jul 18, 2018, 12:54 PM UTC

mozumder wrote: post #20

eisstrom wrote: post #16

Earlier quoted context omitted.

The advantage of MUSE is that you get all color information, i. e. the flux at any wavelength from blue to red. In principle, one can use this together with the sensitivity curve for our eyes to construct a natural image. In this case, I think, they tried to imitate the color scheme from the Hubble image which is more limited. In short: Not sure how realistic this is, but one could make a realistic image from the new…

So MUSE is hyperspectral? there's a full spectrograph at each pixel?

Exactly! One datacube that comes out from the instrument contains 300 x 300 spectra. This is actually the main capability of the instrument which has 24 individual spectrographs. Here's a nice animation of the path the light takes inside MUSE: https://www.youtube.com/watch?v=-fh2Y6Zyhwc&feature=youtu.be...

Re: Supersharp Images from New VLT Adaptive Optics

#23

Post by eisstrom » Wed, Jul 18, 2018, 12:57 PM UTC

nabla9 wrote: post #18

eisstrom wrote: post #15

Earlier quoted context omitted.

We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/united…

Does adding more lasers fix the field of view problem?

This is very much unexplored territory, but ESO thinks so. The ELT (https://www.eso.org/public/teles-instr/elt/) will use more lasers but the exact configuration is still work in progress, as far as I know.

Re: Supersharp Images from New VLT Adaptive Optics

#24

Post by modzu » Wed, Jul 18, 2018, 1:01 PM UTC

Jaruzel wrote: post #10

eisstrom wrote: post #5

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

Are the images natural colour, or have they been 'enhanced' in any way? i.e. is Neptune really that blue?

here's a natural color image of neptune:

https://upload.wikimedia.org/wikipedia/commons/6/63/Neptune-...

Re: Supersharp Images from New VLT Adaptive Optics

#25

Post by dghughes » Wed, Jul 18, 2018, 1:21 PM UTC

raverbashing wrote: post #2

This one is impressive https://www.eso.org/public/images/eso1824c/

I think this one is even more impressive https://www.eso.org/public/images/eso1824d/

If I understand correctly the middle and the image on the right are the same thing, both taken by VLT array. But the right is using the new MUSE technique.

Re: Supersharp Images from New VLT Adaptive Optics

#26

Post by skykooler » Wed, Jul 18, 2018, 1:36 PM UTC

eisstrom wrote: post #15

appleflaxen wrote: post #8

Earlier quoted context omitted.

the article makes it sound like the approach is so effective that it makes space-based telescopes unnecessary. is that true? does this mean that we should simply use ground-based 'scopes with adaptive optics?

We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/united…

Do the lasers create light pollution problems for the telescopes?

Re: Supersharp Images from New VLT Adaptive Optics

#27

Post by SiempreViernes » Wed, Jul 18, 2018, 1:43 PM UTC

eisstrom wrote: post #15

appleflaxen wrote: post #8

Earlier quoted context omitted.

the article makes it sound like the approach is so effective that it makes space-based telescopes unnecessary. is that true? does this mean that we should simply use ground-based 'scopes with adaptive optics?

We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/united…

The Hubble field of view is pretty small too, something like 25 arcseconds the internet tells me.

Re: Supersharp Images from New VLT Adaptive Optics

#28

Post by yread » Wed, Jul 18, 2018, 1:52 PM UTC

eisstrom wrote: post #22

mozumder wrote: post #20

Earlier quoted context omitted.

So MUSE is hyperspectral? there's a full spectrograph at each pixel?

Exactly! One datacube that comes out from the instrument contains 300 x 300 spectra. This is actually the main capability of the instrument which has 24 individual spectrographs. Here's a nice animation of the path the light takes inside MUSE: https://www.youtube.com/watch?v=-fh2Y6Zyhwc&feature=youtu.be...

Awe-inspiring. You can see the individual spectrographs at https://youtu.be/-fh2Y6Zyhwc?t=1089

Re: Supersharp Images from New VLT Adaptive Optics

#29

Post by dekhn » Wed, Jul 18, 2018, 1:54 PM UTC

vanderZwan wrote: post #14

eisstrom wrote: post #5

I'm a PhD student working with data of globular clusters from this instrument for quite some time now. I will be happy to answer your questions!

> With this new capability, the 8-metre UT4 reaches the theoretical limit of image sharpness and is no longer limited by atmospheric blur. Theoretical limit as in diffraction limited? How will this technology "scale" to other frequencies and resolutions? Related to this diffraction limit: is there any overlap in the advances in microscopy and astronomy? For example, do advances in super-resolution microscopy[0] affec…

In my first year of grad school (1995) our microscopy professor showed us an astronomy adaptive optics paper and said "we're going to do that". Years later, they did that.

Re: Supersharp Images from New VLT Adaptive Optics

#30

Post by eisstrom » Wed, Jul 18, 2018, 1:54 PM UTC

SiempreViernes wrote: post #27

eisstrom wrote: post #15

Earlier quoted context omitted.

We can achieve a very high resolution from the ground but only in a very small field of view. To cover one typical HST image with MUSE at the VLT, we would need a mosaic of hundreds of exposures. The reason for this are the four artificial guiding stars from the lasers. The closer they are together on the sky, the more atmospheric distortion you can correct. Here is an image of them: https://www.eso.org/public/united…

The Hubble field of view is pretty small too, something like 25 arcseconds the internet tells me.

I was comparing it to HST WFC3 with a field of view of 160 x 160 arcsec^2 (https://www.spacetelescope.org/about/general/instruments/wfc...). Thats about 450 times larger than the MUSE narrow-field mode FOV.

I think you mean the high-resolution mode of the ACS instrument (https://www.spacetelescope.org/about/general/instruments/acs...) but that is broken and it was not repaired during the last HST service mission.