Sunday, October 21, 2012


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 800mm TelyR.  But not many are aware that Leica made a lens twice as long, a 1600mm f/5.6 Apo-Telyt-R.  It was delivered in 2006 on special order from 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 prototype is on display at the Leica factory showroom in Solms, Germany, and can be admired there.

Leica 800mm f/6.3 Apo-Telyt-S

Leica 1600mm 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.

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 Kec 1 and 2k 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 took a big step closer to becoming reality in June of this year, when final approval came from the scientific consortium backing the new observatory.

Plans for the mega-telescope, appropriately called the European Extremely Large Telescope (E-ELT), were approved by the governing council of the European Southern Observatory (ESO), officials announced.

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 $1.35 billion at current exchange rates. ESO officials have said that construction is expected to begin sometime this year, with the telescope becoming operational in the early 2020.  Unfortunately, no information regarding its focal length and subsequent speed are available at this time.

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

For more on the subject go to:



  1. Very interesting, especially the data on the telescopes in terms of focal length and speed. I have never seen astronomical telescopes looked upon in those terms.One question, what is the difference between a solid and a segmented mirror?

  2. Solid mirrors have size limitations. It was thought that the 5 meter mirror of the Hale telescope on Mount Palomar was the limit. But the BTA-6 telescope in Russia has a 6 meter mirror. That unit has been plagued by considerable flaws ever since it was first built. The reason for these limitations is weight and the fact that the mirror will actually distort under its own weight. With segmented mirrors the entire mirror is divided in a multitude if hexagon shaped smaller units which, when assembled, will form a large mirror functioning as a single unit. The individual segments are relatively thin and therefore quite light. Their shape is computer controlled via a very sophisticated system which actually reshapes the individual segments to the highest degree of accuracy. This way it is also possible to compensate for atmospheric disturbances which ultimately makes these telescopes as sharp and accurate as orbital telescopes like the Hubbel telescope, for instance. The E-ELT will use several laser beams to probe the atmosphere for any possible disturbances to an even higher degree of accuracy and compensate for it accordingly. It will be the most amazing telescope ever built.

  3. Could you give us a guess as to the speed of the E-ELT, to have some comparison to other large telescopes?

  4. Well, we 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. 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.

    1. I should add that the known specs for the E-ELT indicate that it will be 12 times more sensitive than anything else currently in use. That is an increase of 3 1/2 stops. Considering that the large binocular telescope has a maximum aperture of f/1.142, that would bring the E-ELT to approximately f/0.3. That in turn indicates a focal length of approximately 12 meters

  5. I wonder what the lever is on the side of the 1600mm Apo-Telyt?

  6. I have no idea. I'll let you know once I find out.

    1. I put out that question over the internet. Nobody really knows (other than some people at Leitz) and very little is known about the lens. The general consensus is that it is not a lever but a handle. This is actually installed on both sides of the lens.
      I will definitely fins out about it on my next visit to Solms.

    2. I wish there was an editing function for the comment section.

      Make that 'find out about...'

    3. One answer I received was indicating quite a different purpose. It read
      "There's a built in fridge and that's the handle to open the fridge to get the beers out."

    4. Is it big enough to hold a bottle wine instead?

  7. Certainly not a magnum, and I think even a regular 750ml bottle might be too big. But you could always use a 1/3 liter bottle, like what Trockenbeerenausleses or Eiswein usually come in. In addition, there are also the so-called piccolo champagne bottles. Also, let's not forget that the lever/handle is on both sides of the lens, so ti should be possible to store the wine on one and the beer on the other side. But the double fridge is only available on the deluxe model. The others have only one fridge and just a storage compartment on the opposite side;-)

    1. But the lens is not available in either version.

    2. Of course the lens is available. How else did the Sheikh obtain it. It is not officially part of what Leica is offering in their list of goods, but as the 2 million cost to the Sheikh indicates, pass on another 2 million, and the lens is yours. The price for the deluxe version is available upon request.

  8. I don't see much sense in writing about telescopes because Leica is not involved in their manufacture.

  9. I respectfully disagree. To gain a better understanding of optical instruments in general will inevitably lead to a better understanding of Leica as well.