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Captain's Log

October 2015


Telescopes - From Spyglasses to Space Exploration

Telescopes - From Spyglasses to Space Exploration

'The camera cannot lie...' Whoever coined that expression knew precious little about photography - or human nature. Because 'trick' photography has been around as long as tricky photographers. Double exposure techniques convinced gullible Victorians that they were looking at pictures of ghosts or fairies - and then there was the telephoto lens.

Nowadays an essential piece of kit for the paparazzi and wildlife cameramen who want to get up close and personal, the first telephotos were simply telescopes screwed onto the front of cameras. As for telescopes themselves, they go back a lot further.

Shrinking distances
In the 14th century convex lenses were developed to correct farsightedness. People with the opposite problem (shortsightedness) had to wait approximately 100 years until it occurred to  someone that an opposite shaped lens - concave - was the answer. Then in 1608 a Dutch optician called Hans Lippershey discovered that looking through two lenses some distance apart made distant objects appear closer. A year later Galileo began constructing telescopes. These ranged from three times magnification to an impressive thirty times and enabled him to observe craters and mountain ranges on the moon.

'I see no signal'
Relatively low-powered telescopes or spyglasses were quickly adopted by the military, both on land and sea. Naval commanders on both sides in the Anglo-Dutch Wars of the 17th century used them to keep an eye on the enemy. And in the Napoleonic Wars, telescopes made signalling with flags over greater distances possible. Even if Nelson did turn a blind eye occasionally.

Taking the long view
But these early telescopes were beset by a basic optical problem. The images viewed were distorted by haloes of coloured light - attractive but detrimental to scientific observation. Two solutions were proposed. Johannus Hevelius realised that the longer the telescope was, the closer together the different colours would be at the focal point, resulting in a reduced halo effect and a clearer view. Not a man to do things by halves, Hevelius built a telescope 140 feet long. In theory this should have given a sharp image. However it was almost impossible to keep the two lenses aligned because the supporting structure - essentially a long tube - couldn't be made rigid enough.

It's all done with mirrors
Isaac Newton - the greatest natural philosopher of the age - came up with an alternative answer. He designed and built a reflecting telescope using a two inch diameter concave spherical mirror, a flat, angled secondary mirror and a convex eyepiece lens. Newton's telescope showed the potential of this kind of instrument. Objects could be magnified millions of times - far beyond what was possible with lenses alone.

Three hundred years of R&D
For the next three centuries telescopes were refined and perfected. Experiments in lens and mirror design and greater precision in optical engineering resulted in better, brighter and bigger images from further and further away. But all technologies have their limitations and by the early 20th century optical astronomical telescopes had been developed about as far as they could be. The next step was revolutionary.

Viewing the invisible
In 1945 Sir Bernard Lovell established the Jodrell Bank Experimental Station, now known as the Jodrell Bank Observatory. This was to play a crucial part in the new science of radio astronomy. Today Jodrell bank is home to four giant telescopes including the third largest steerable version in the world. Using a technique known as 'gravitational lensing' Jodrell bank is involved in the forefront of radio telescope technology, detecting objects invisible to the eye, including the mysterious Dark Matter that dominates cosmic structure.

The power to see the glory
Of course what is observable from Earth is limited. So in the spirit of meeting the problem half way, on April 25 1990 the Hubble Space Telescope was launched. Its role - job description if you like - was ambitious. This included tasks such as 'measure the age and size of the universe', 'search for our cosmic roots' and 'unlock the mysteries of galaxies, stars, planets and life itself'. So no pressure then. Orbiting approximately 380 miles above the Earth's surface, Hubble has produced unprecedented images - photographs that are quite literally 'out of this world'

It's a long way from the telephoto lens and a whole lot further from Hans Lippershey's first telescope. Makes you wonder what the next 400 years will bring...

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