Sharpest Images With "Lucky" Telescope 165
igny writes "Astronomers from the University of Cambridge and Caltech have developed a new camera that gives much more detailed pictures of stars and nebulae than even the Hubble Space Telescope, and does it from the ground. A new technique called 'Lucky imaging' has been used to diminish atmospheric noise in the visible range, creating the most detailed pictures of the sky in history."
Compared to adaptive optics? (Score:5, Informative)
Overall, a fairly clever technique. I wonder how this compares to adaptive optics [wikipedia.org], which is another solution to this problem. In adaptive optics, a guide laser beam is used to illuminate the atmosphere above the telescope. The measured distortion of the laser beam is used to distort the imaging mirror in the telescope (usually the mirror is segmented into a bunch of small independent sub-mirrors). The end result is that adaptive optics can essentially counter-act the atmospheric distortion, delivering crisp images from ground telescopes.
I would guess that adaptive optics produces better images (partly because it "keeps" all incident light, by refocusing it properly, rather than letting a large percentage of image acquisitions be "blurry" and eventually thrown away), but adaptive optics are no doubt expensive. The technique presented in TFA seems simple enough that it would be added to just about any telescope, increasing image quality at a sacrifice in acquisition time.
You Too Can Get Lucky. (Score:5, Informative)
DIY [cam.ac.uk].
Re:Exposure Time? (Score:5, Informative)
Re:Yawn (Score:4, Informative)
Dr. Mackay? (Score:3, Informative)
Re:But surely... (Score:5, Informative)
Additionally, while they don't mention details in the article, I presume they have a specially designed camera. This is an old technique, but it's generally limited to very bright objects due to something called readout noise. Basically all CCD's produce an additional signal due to the process of reading out the data. This limits the effectiveness of repeated short observations to sources which are much brigher than this noise, since the noise also grows linearly with the number of images taken.
To image distant galaxies you typically have to take exposures of one to several hours, and thus this technique isn't useful.
Doug
Many amateurs already do this (Score:5, Informative)
Look at the planetary images here [imeem.com] for my attempts at this technique.
Comparison to hubble... (Score:5, Informative)
Probably they can push their technique harder than this initial image suggests (it was mainly comparing the "lucky" image with a conventional, blurry, ground-based image)... But I just thought it would be good to show Hubble's pictures alongside.
Re:But surely... (Score:5, Informative)
They are using a new kind of CCD that somehow lowers the noise floor. Details are at:
http://www.ast.cam.ac.uk/~optics/Lucky_Web_Site/L
In fact this site (same basic place) is much more informative than the press release and answers a lot of questions:
http://www.ast.cam.ac.uk/~optics/Lucky_Web_Site/i
Re:Compared to adaptive optics? (Score:5, Informative)
link (Score:1, Informative)
Re:You Too Can Get Lucky. (Score:2, Informative)
This is indeed no news to amateur astronomers. This technique has been used extensively by planetary imagers in recent years to take amazing photos of Jupiter, Mars and Saturn. The basic tools are a good webcam to take AVI files and Registax to proccess the frames. Take a look to Damien Peach's best images [damianpeach.com].
As for pro, there is even an article in Wikipedia about it: Lucky imaging [wikipedia.org]: "Lucky imaging was first used in the middle 20th century, and became popular for imaging planets in the 1950s and 1960s (using cine cameras or image intensifiers). The first numerical calculation of the probability of obtaining lucky exposures was an article by David L. Fried in 1978."
In order to throw away many frames and retain only those of high quality, better have a bright object or a big telescope. In this case, the astronomers had been able to image a faint nebula.
Blue Peter for non-Brits (Score:5, Informative)
using 'Blue Peter' technology
Blue Peter [bbc.co.uk] is a BBC childrens show. Blue Peter Technology is effectively something so simple a child could do it.
Re:Yawn (Score:4, Informative)
Far infrared is a different story, and you're absolutely correct there.
Common use with amateurs, but has issues (Score:4, Informative)
I'm curious though about how they deal with some of the "features" you get to see with this technique. It's *very* easy to stack a few hundred images, run Registax's sharpening filter and get some interesting pictures of stuff that doesn't really exist. I'm not sure I really trust the fine detail in my photos- unless I see it in another taken a few hours later it may well not be real.
Re:Yawn (Score:4, Informative)
See here [noao.edu], for example, for more information.
There are wavelength ranges in the NIR where the atmosphere is indeed transparent (J,H and K bands, for example); but the atmosphere is opaque at most NIR wavelengths (and, even at those IR wavelengths where the atmosphere is transparent, the transmittance is lower than at visible or radio wavelengths). See here [caltech.edu] for more info.
Re:Compared to adaptive optics? (Score:3, Informative)
No, they propose that it be used together with adaptive optics. The research that was done to produce this press release was actually done at the Mount Palomar observatory, which was completed in 1947 [caltech.edu] and most certainly does not feature adaptive optics.
From the article:
The technique could now be used to improve much larger telescopes such as those at the European Southern Observatory in Chile, or the Keck telescopes in the top of Mauna Kea in Hawaii. This has the potential to produce even sharper images.
(Emphasis mine)
Space-based telescopes aren't dead yet... (Score:3, Informative)
Re:But surely... (Score:3, Informative)
Now there is a new type of CCD with a built in digital signal multiplier that precedes the readout step in each individual pixel. You can simply select an appropriate multiplier that gives pixel values that fall nicely in the middle of the register width and when you read out the value, any noise can simply be subtracted away because you know that it will be much less than the signal value you are looking at.
Re:Not convinced by TFA (Score:1, Informative)
- The Earth rotates in 24h
- Hubble orbits in 90 min
so Hubble cannot peer "hours at a time", but ground telescopes can.
Re:Lucky Imaging (Score:5, Informative)
So it looks like each frame is shifted as a whole rather than each individual pixel. Which makes sense from the description of the process, since the theory is that the images you're picking in the Lucky Imaging technique are high-quality images with a random offset due to the atmosphere.
Re:If they can do this from earth... (Score:3, Informative)
Lucky Imaging relies on the fact that every so often, a really high-quality image makes it through the atmosphere almost unperturbed (based on the Kolmogorov model [cam.ac.uk] of turbulence). While I don't know whether the same model can be applied to cosmic gas clouds, there may be another model that could accurately model the phase distortions those clouds impress upon a wavefront.
To achieve this one must take many very short-exposure (compared to the time-scale of atmospheric turbulence, or gas-cloud turbulence in the case we're considering) images of the source. However, distant (or dim) objects often require reasonably long exposure times in order to collect a large enough amount of light to be able to see the image. The problem with this technique may simply be that the exposure time necessary for the Lucky Image algorithm to work is too short to actually collect enough light to create a good image in the first place.
Email from the principle investigator (Score:2, Informative)
Re:Comparison to hubble... (Score:3, Informative)
Re:Lucky Imaging (Score:3, Informative)
http://www.astronomie.be/registax/html/multi_oper
Re:Blue Peter for non-Brits (Score:3, Informative)
Not quite squinting, but still an eye trick