Large Synoptic Survey Telescope (LSST Update

World’s most powerful digital camera gets the go-ahead

A smartphone with a 16-megapixel camera may seem cutting edge, but it won’t impress astronomers now that the US Department of Energy’s SLAC National Accelerator Laboratory has given the green light to start constriction of the world’s largest digital camera. With a resolution of 3.2-gigapixels (enough to need 1,500 high-definition television screens to display one image), the new camera is at the heart of the 8.4-meter (27.5-ft) Large Synoptic Survey Telescope (LSST) now under construction atop Cerro Pachón in Chile.

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Excellent.

Is this going to be the world’s largest lens?

No good for photographing flowers unless they are on Mars.

mollwollfumble said:

Is this going to be the world’s largest lens?

Let’s compare with some other large ones (excluding Fresnel lenses here).

The LSST front lens is about 1.4 metres diameter.

Yerkes observatory, largest still-existing refracting telescope, has a lens 1.02 metres diameter.
Paris 1900 exposition, lens now scrapped, had a lens 1.25 metres diameter.
Siding Springs has a Schmidt telescope with a lens 1.2 metres in diameter.
The Samuel Oschin telescope at Palomar has a lens 1.22 metres in diameter.
The Alfred-Jensch-Telescope at the Karl Schwarzschild Observatory in Tautenburg, Thuringia, Germany is the largest Schmidt camera in the world. It’s 2 metres in diameter, but the lens is only 1.34 metre across.

So this could be the word’s largest ever non-Fresnel lens.

So the overall diameter is 1.65 metres and the three lens diameters are 1.55, 1.10 and 0.76 metres.

Fresnel lenses come bigger. According to wikipedia a first order Fresnel lens for use in a lighthouse has a maximum diameter 2590 mm. The largest Fresnel lenses are called hyper-radiant or hyper-radial Fresnel lenses. One such lens was on hand when it was decided to build and outfit the Makapuu Point Light in Hawaii. Rather than order a new lens, the huge optic construction is 3.7 metres (12 ft) tall with over a thousand prisms.

The following link gives lots of photographs and drawings of these huge hyper-radiant/hyper-radial Fresnel lenses, but annoyingly gives only the focal length, not diameter, which is understandable because most aren’t circular.
http://uslhs.org/hyper-radial-lenses

This immediately begs the question ‘why don’t telescopes and large cameras use Fresnel lenses?’

mollwollfumble said:

Let’s compare with some other large ones.

Yerkes observatory, largest still-existing refracting telescope, has a lens 1.02 metres diameter.
Paris 1900 exposition, lens now scrapped, had a lens 1.25 metres diameter.
Siding Springs has a Schmidt telescope with a lens 1.2 metres in diameter.
The Samuel Oschin telescope at Palomar has a lens 1.22 metres in diameter.
The Alfred-Jensch-Telescope at the Karl Schwarzschild Observatory in Tautenburg, Thuringia, Germany is the largest Schmidt camera in the world. It’s 2 metres in diameter, but the lens is only 1.34 metre across.

This is interesting. The lens in the Kepler spacecraft (planet finder extraordinaire) is a full 0.95 metre diameter. That has to be by far the largest lens in any space telescope.
The largest lens used in the Apache Point SDSS telescope is 0.802 metres in diameter. (Using a lens system designed by an Australian)
ditto for the largest lens to be used in the Giant Magellan Telescope, 0.802 metres, second largest 727 mm.
The lenses in Pan-Starrs are “only” 0.5 metres in diameter.

There are other large telescopes containing lenses, including The Irénée du Pont Telescope, The Henrietta Swope Telescope, The ESO 3.6 m telescope on La Silla. Look up “Gascoigne corrector”.

More lenses.

“Arizona Optical Systems LLC selected to manufacture and test 850mm diameter aspheric corrector lenses for the Dark Energy Spectroscopic Instrument (DESI) project. The Mayall 4-meter telescope at Kitt Peak Observatory near Tucson is slated for a new study to measure the expansion of the universe. This will be accomplished through a 4 year survey, beginning in 2018”.

AOS will also make the LSST camera lens.