Restoring the Alcock Telescope

Alcock1

Anyone with even a casual interest in the history of British amateur astronomy will be familiar with the legacy of Peterborough schoolteacher, George Alcock (1912-2000). Widely regarded as the greatest visual observer to live under English skies, Alcock was the discoverer of five comets and five novae. In his long career, he had memorised the positions and brightness of at least 30,000 stars, scanning the skies mostly with a modest collection of binoculars on every available clear night.

What is less well known is that George conducted a series of planetary studies with an old 3.9” (100mm) f/12.5 refractor made by Ross of London. The telescope was originally owned by Major A.E. Levin, a past Director of the Computing Section of the British Astronomical Association (BAA) and its President from 1930-32. The telescope was believed to be mounted on a wooden tripod (now sadly lost) but it is notable that the instrument was billed apochromatic. It thus would have been very expensive but still affordable to the well-to-do Levin. After his death in 1939, the instrument was held in trust by the BAA and shortly thereafter loaned to George Alcock, who used it to conduct his regular comet sweeps, as well as to embark upon a visual study of Jupiter.

The Alcock 4" f/12.5 triplet refractor on an old Cooke equatorial mount.

The Alcock 4″ f/12.5 triplet refractor on an old Cooke equatorial mount. Image credit: Denis Buczynski.

 

 

 

 

 

 

 

 

 

 

 

 

 

Alcock’s drawings of the Giant Planet, produced during November and December of 1952, reveal extraordinary attention to detail. But as Kay Williams recounted in her biography of the man (Under an English Heaven: The life of George Alcock, (1996), Genesis Publications) Alcock’s Jupiter work was not universally received with gratitude. Some prominent members of the BAA were sceptical about the level of detail Alcock divined from his 4 inch Ross refractor and he became dispirited as a result. Indeed, he soon abandoned BAA planetary work altogether. What’s more, as his interest in comet and nova searches intensified, Alcock came to prefer the wider fields of view served up by his 25 x125 binoculars and, as a result, the telescope was stored away in its wooden box under his bed for many decades.

After he passed away in 2000, the BAA presented the Ross refractor to veteran BAA member and personal friend of George Alcock, Denis Buczynski, who now observes from the crystal clear skies of Rosshire, in Northern Scotland. But from the get go, Denis had noticed that there was something amiss with the images the ‘Alcock’ was producing. Recently, he contacted me about the telescope and asked if I’d take a look at it for him. When I heard about its pedigree, how could I possibly resist!

                                        A Rare Beauty!

The telescope arrived in a beautiful wooden box, solid oak by the look of it. The instrument is fashioned from solid brass, and painted a matt black. And it’s reassuringly massive; weighing in at 30 pounds. A quick daylight test of the optics revealed something was indeed array, the image being incapable of achieving a sharp focus. Subsequent star testing demonstrated the presence of severe coma, although colour correction looked really good. Clearly, one or more of the elements had become misplaced over the years and so required expert adjustment.

The finely crafted Ross objective (uncoated) at the heart of the telescope. Image credit: Denis Buczynski.

The finely crafted Ross objective (uncoated) at the heart of the telescope. Close inspection of the glass revealed a few tiny air bubbles ( normal for an O.G. of this age). Image credit: Denis Buczynski.

 The apochromatic billing of the instrument led me to suspect it had a three element objective, perhaps of Zeiss (Germany) or British (Taylor) origin. The latter were normally made in longer focal lengths (typically f/18), which lent greater credence to the German origin of the objective. Certainly, Ross of London did import glass from the German optical giant in fashioning some of their finest object glasses, although on this occasion, we were unable to offer a definitive proof of origin for the optics.

The interior of the tube was impressively blackened and well baffled. The focuser came as a surprise though, expecting as I was a single wheel. Instead, it was more akin to what you’d find on a modern telescope (with two focus knobs). The lens cell – which I might add, is exquisitely well made – was removed from the instrument and despatched to expert optician, Es Reid, in Cambridge. Es quickly confirmed its triplet design, having two dense positive glasses symmetrically positioned either side of a light negative crown. A few tiny air bubbles were also observed on the crown elements – a characteristic which was rather common in glass of this age – but which had no effect on the performance of the instrument. Es was also very impressed at its lack of secondary spectrum.

Check out the sable innards of the Alcock telescope.

Check out the sable innards of the Alcock telescope.

 

 

 

 

 

 

 

 

 

 

After further tinkering, Es had pinned down the problem to a missing lead spacer which he replaced. The optics were fairly grubby but had good clear surfaces and no devitrification (a common problem in early triplets of this pedigree). Needless to say, Es’ prognosis came as a great relief to both Denis and I, and all that remained to be done was to reunite the object glass with the tube.

 

The unusual focuser on the historic Ross refractor, which is more in step with contemporary models.instrumnets

The unusual focuser on the historic Ross refractor, which is more in step with contemporary instrumnets.

 

 

 

 

 

 

 

 

 

 

 

                 

                                                                  

Ad Astra!

The newly cleaned and adjusted object glass was star tested at the first available opportunity and I was delighted to see that all was well. Testing at high powers (>200x) using a modern wide angle eyepiece on the bright summer star, Vega, the telescope rendered a perfectly round Airy disk, with almost perfect symmetry in the de-focused star image. Spherical correction appeared excellent. Only the merest trace of astigmatism was noted but at a level that I judged wholly negligible. Colour correction was superlative, hardly a trace on brilliant Vega and at least as good as any modern triplet apochromat I’ve had the pleasure of using. Neither was there any sign of lateral colour, either on axis or when the star was displaced to the edge of the field. All in all, a most excellent result!

Further testing on high resolution targets revealed textbook perfect performance. All four components of the Lyra Double Double (Epsilon 1 & 2 Lyrae) were beautifully sharp, the subtle colour difference between the components being clearly on display. It passed much tougher tests too; the devilishly faint companion to Delta Cygni was easily resolved, as was Pi Aquilae and the beautiful triple system Iota Cassiopeiae. Lunar images were tack sharp with no colour visible round crater limbs at the day-night terminator. A brief look at Jupiter at 120x in the small hours of the morning revealed excellent definition and no false colour. Cruising the summer Milky Way through Cygnus was a joyous event, the many shoals of stars appearing like pinpoints against a coal black hinterland. At the time of writing, the bright Nova Delphini appeared in the sky and I eagerly turned the telescope toward it to watch it slowly fade over the subsequent days and weeks. Intriguingly, this was the only nova appearing in Delphinus since Alcock’s famous 1967 discovery of HR Delphini!  How uncanny!

                               

                                    Re-visiting Alcock’s Jupiter Drawings

The superlative quality of the restored instrument throws fresh light on the drawings of Jupiter made by Alcock in the Winter of 1952. Certainly, the great observer could not have recorded the fine Jovian atmospheric details with a telescope that was substandard or mis-aligned. After restoration, the colour and spherical correction were found to be near perfect. While the quality of the optic certainly played its part, the archives reveal no evidence that the original owner- Major A.E.Levin –  saw anything out of the ordinary whilst using the instrument compared with those employing conventional achromatic optics.

Examples of Alcock’s sketches of Jupiter in the Winter of 1952, conducted with the 4-inch Ross telescope. Reproduced with permission from the BAA.

Examples of Alcock’s sketches of Jupiter in the Winter of 1952, conducted with the 4-inch Ross telescope. Reproduced with permission from the BAA.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Alcock’s subsequent discovery and visual rendering of the comets he had discovered  (see Table 1.) clearly reveal his exceptional eyesight (he recorded details in the head and tails of comets that many others had failed to notice visually but were subsequently confirmed photographically). One other thing struck me about Alcock’s drawings was the high magnification he employed (200-250x). Having compiled a study of the average magnifications used on Jupiter by a variety of observers throughout the last two centuries, I found that while there is considerable variation between some observers, they tended to gravitate toward an arithmetic mean of about 30x per inch of aperture, irrespective of their aperture. This may have some bearing on the details recorded by Alcock.

All in all though, despite its great age, the telescope is one of the finest 4 inch refractors I have had the pleasure of using and I considered it a great privilege to have played a small part in its restoration.

 

I would like to thank Denis Buczynski for giving me the opportunity to bring George Alcock’s telescope back to life. I would also like to extend my thanks to Es Reid for his professional re-adjustment of the old object glass and Martin Mobberley for providing the photograph of George Alcock.

  Table 1.
                                  The Discoveries of George Alcock
1959 Comet C/1959 Q1 (Alcock) = 1959e.
1959 Comet C/1959 Q2 (Alcock) = 1959f.
1963 Comet C/1963 F1 (Alcock) = 1963b.
1965 Comet C/1965 S2 (Alcock) = 1965h.
1967 HR Del = Nova Del 1967.
1968 LV Vul = Nova Vul 1968 No 1.
1970 V368 Sct = Nova Sct 1970.
1976 NQ Vul = Nova Vul 1976.
1983 Comet C/1983 H1 (IRAS-Araki-Alcock) = 1983d.
1991 V838 Her = Nova Herculis 1991.

 

 

 

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2 thoughts on “Restoring the Alcock Telescope

    • Hello Neil,

      Thank you for your comments. It was a pleasure to help give that old telescope new light. Denis informs me it is still giving excellent images up north. It is a historically significant telescope and was used by one of Britain’s most dedicated visual observers.

      Regards,

      Neil.

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