Friday, August 22, 2014


A while ago I got into a discussion about the longest telephoto lenses ever made, by Leica but also in general.  Most Leica enthusiast are aware of the awesome 800 mm f/6.3 TelyR, the longest lens after the 560 mm f/6.8 Telyt-R.  But not many are aware that Leica made a lens twice as long, a 1600 mm f/5.6 Apo-Telyt-R.  It was delivered in 2006 on special order to a rich photography aficionado, Sheikh Saud Bin Mohammed Al-Thani of Qatar, at a price of 16 million Hong Kong Dollars - the equivalent of 2,064,500 US dollars. The lens is the only one ever sold, but a another one was on display at the Leica factory showroom in Solms, Germany, and will most likely be shown at the new Leica headquarters in Wetzlar.

Leica 560 mm f/6.8 Telyt-R on Leica M5, Visoflex 3, Bellows2

Leica 800 mm f/6.3 Apo-Telyt-S

Leica 1600 mm f/5.6 Apo-Telyt-R

Unfortunately, little is known about the technical specifications of the lens. It has a bayonet mount for Leica's R-series cameras, is approximately 1.2m long (1.55m with lens hood attached), has a maximum lens barrel diameter of about 42cm, and weighs no less than 60kg.  With a focal length of 1600mm, it covers a diagonal angle of view of merely 1.5 degrees. The lens should be compatible with Leica's 1.4x and 2x APO-teleconverters, increasing the focal length to 1:8/2240mm and 1:11/3200mm respectively.  With the Leica R afapter, it could also be used on the Leica M and Leica M-P.

Leica M8 camera sitting inside the lens hood

Getting sharp images from such a behemoth of a lens is a major challenge and requires a very solid tripod. The Danish Leica expert Thorsten Overgaard reported that Sheikh Al-Thani commissioned a specially-equipped Mercedes four wheel drive to carry his expensive lens and move it around.

But this is very little compared to the truly longest and most powerful lenses ever made.  Actually, the word lens is somewhat misleading because I am talking about astronomical telescopes.  People have argued that a telescope is not really a lens, yet I argue it is.  Astronomical telescopes routinely are used to take photographs.  That, in principle, makes them lenses just like any other telephoto; they are just a lot longer and faster.

One of the main aspects of an astronomical telescope is its light gathering power, or speed as we refer to it in photography.  In this regard I have come up with some rather astonishing numbers.

Currently, the largest telescope in operation is the Gran Telescopio Canaris.  Its main mirror has a diameter of 10.4 meter (34.12 foot).  The actual focal length is 16.5 meter which corresponds to a 16,500mm f/1.586 lens.  Similar in size are the Keck 1 and Keck 2 telescopes on Mauna Kea in Hawaii.  They have a diameter of the main mirror of 10 meter (32.8 foot).  Their focal length is 17.5 meter, making them 17,500mm f/1.75 lenses.

Gran Telescopio Canaris

Keck 1 and 2

The segmented mirror of Keck 2

The Large Binocular Telescope at the Mount Graham International Observatory in Arozona consists of two parallel telescopes which can be combined for simultaneous viewing.  It has currently the largest light gathering power of any earthbound telescope with a focal length of 9.6 meter, making it a 9,600mm f/1.142 lens.

Large Binocular Telescope

By these figures we can definitely see that there is a correlation between focal length and actual speed.  This becomes especially obvious when considering the BTA-6 telescope of the Special Astrophysical Observatory in Karachay–Cherkessia, Russia.  It has a mirror with a diameter of 6 meter (19.69 foot).  Apparently it has the longest focal length of any telescope currently in use with 26 meter (85.3 foot), effectively making it a 26,000mm f/4 lens.

The large structure to the right is a special crane used to service the installation

The 6 meter, solid mirror of BTA-6

A European project to build the largest optical telescope on Earth started to be built in fall of 2012, after getting the final approval from the scientific consortium backing the new observatory.

In fall of 2012 construction of the largest telescope in the world began after gaining the final approval by the governing council of the European Southern Observatory (ESO) earlier that year.

The E-ELT will be a 129-foot (39-meter) segmented-mirror telescope sited atop a mountain called Cerro Armazones in northern Chile, close to ESO’s Paranal Observatory. It will be many times more sensitive than any other instrument of its kind, researchers said.

An artist rendering of the E-ELT.
Please note the size of the car and the person at the lower left for scale

The huge telescope will collect at least 12 times more light than today's largest optical telescopes, allowing astronomers to probe a variety of high-priority cosmic questions. Scientists will use it to help search for habitable alien planets, for example, and to study the nature and distribution of dark matter and dark energy, the mysterious stuff thought to make up most of our universe but which astronomers have yet to detect directly.

"The telescope is set to revolutionize optical and infrared astronomy," said Isobel Hook of the University of Oxford, the United Kingdom's E-ELT project scientist, in a statement. "Its unique combination of sharp imaging and huge light collecting area will allow us to observe some of the most exciting phenomena in the universe in much better detail."

Building the E-ELT is expected to cost 1.083 billion euros, or roughly $1.46 billion at current exchange rates. ESO officials estimate the telescope becoming operational in early 2020. 

No data regarding the actual speed of the telescope has been published so far.  We do know that the telescope's main mirror has a diameter of 39 meters. With a focal length of 39 meters, that would yield a maximum aperture of f/1. Looking at some of the other large telescopes throughout the world, they all seem to have a focal length under 20 meters. Taking a 20 meter focal length would yield a maximum aperture of f/0.51. Consideration that this telescope is designed to gather at least 12 times more light than the largest optical telescopes currently in operation, this could translate to an aperture of potentially f/0.3.  With other words, this telescope will be amazingly fast, especially if one considers that the fastest production lens for photography is the 50mm f/0.95 Leica Noctilux.

Very impressive instruments indeed.  But for the time being I will stay with my 400 and 800 mm lenses.  They are a lot more portable, although also a lot slower.


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