A 'giant' rising in the desert: World's largest telescope comes together (photo)

[Admin]

Construction of the world's largest telescope moves forward with progress of the dome and housing for the primary mirror.

A 'giant' rising in the desert: World's largest telescope comes together (photo) : Read more

 

[brunodoggy]

At first glance, I thought someone was building a Death Star!

 

[damnyankee36]

..."The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3)"...

Wouldn't Mount Palomar's 200", (16.7'), mirror beat the size of the 14' secondary mirror of the ELT?

 

[George²]

..."The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3)"...

Wouldn't Mount Palomar's 200", (16.7'), mirror beat the size of the 14' secondary mirror of the ELT?

Well, it's easy when you compare the size of a primary mirror to the size of a secondary mirror. In this sense, today the main telescope at the Palomar Observatory is surpassed by about 20 telescopes. If we count only telescopes with a non-segmented mirror, then the Hale telescope is only 15th in the ranking of mirror sizes.

 

[DrDave]

..."The 14-foot (4.25-meter) mirror — the largest convex mirror ever produced — will reflect light collected by M1 to the 12-foot (3.75-meter) tertiary mirror (M3)"...

Wouldn't Mount Palomar's 200", (16.7'), mirror beat the size of the 14' secondary mirror of the ELT?

The 200" mirror on Mount Palomar is not a convex mirror but a concave one.

 

[Marc2001]

Will it outperform the JWST?

 

[DrDave]

Will it outperform the JWST?

Well its horses for courses there. It has sufficient collecting area that you'll be able to do things like spectroscopy of the atmosphere of planets at nearby stars. Something JWST can't really do as well, however JWST which is above the atmosphere and all the distortions it brings will be unmatched in terms of the sort of high resolution images it will be able to get.

 

[starman2]

I wonder why it even needs a secondary mirror. At that size (14') you could easily position a human observer at the focal point of the primary mirror for the best undistorted viewing. But if they are also talking about a tertiary mirror (3.75 m) then they must mean some type of catadioptric design which gives a greater focal length. But nowhere in the article is any mention of catadioptric, Cassegrain, or Schmidt.

 

[damnyankee36]

The 200" mirror on Mount Palomar is not a convex mirror but a concave one.

Duh, I didn't catch that... Thanks.

Still, they are comparing two solid mirrors. I really don't know if the convex design makes a difference in the difficulty in manufacturing.

 

[billslugg]

The focal length of the primary mirror is 743.4 meters. Such a large structure would be hard to make.

 

[starman2]

I adjusted my viewpoint. Although the ELT is not completed yet, it is obviously a catadioptric design. For a reflector, the truss would be too extended, too heavy, and too expensive - but maybe not impossible. Catadioptric bounces the incoming light back and forth to achieve a long focal length. Long focal lengths mean high power - they're trying for exoplanets.

 

[DrDave]

I wonder why it even needs a secondary mirror. At that size (14') you could easily position a human observer at the focal point of the primary mirror for the best undistorted viewing. But if they are also talking about a tertiary mirror (3.75 m) then they must mean some type of catadioptric design which gives a greater focal length. But nowhere in the article is any mention of catadioptric, Cassegrain, or Schmidt.

You are producing a telescope with a nearly 40 meter diameter the focal point of the primary will be 743 meters away. If you wish to point the telescope at anything I don't think it will be easy to put anything there at all. With telescopes that size you definitely aren't putting humans at the end looking down them either - you will have a suite of advanced imaging sensors. If you are producing a telescope with a nearly 40 meter diameter - you can bet you aren't using primary correcting plates either. If I have that right that's a catopric design rather than a catadioptric design.

The telescope dome will be enormous as it is and they need a convex secondary just so that they can mechanically fit everything in it.

 

[starman2]

You are producing a telescope with a nearly 40 meter diameter the focal point of the primary will be 743 meters away. If you wish to point the telescope at anything I don't think it will be easy to put anything there at all. With telescopes that size you definitely aren't putting humans at the end looking down them either - you will have a suite of advanced imaging sensors. If you are producing a telescope with a nearly 40 meter diameter - you can bet you aren't using primary correcting plates either. If I have that right that's a catopric design rather than a catadioptric design.

The telescope dome will be enormous as it is and they need a convex secondary just so that they can mechanically fit everything in it.

The telescope design is Nasmyth -Cassegrain, a modified form of Cassegrain - so it is some variant of a catadioptric design. They tend to call anything with a large reflecting mirror a 'reflector telescope,' but it doesn't look much like a Newtonian Reflector. Newtonians will have a large extended truss and the ELT appears stout in appearance. Sometimes a human observer (or imaging sensors) can be located at the focal point of a large primary mirror - but apparently that is some other type of telescope.