New Horizons: Using Newtonians for Daylight Applications.

No expense spared to bring you the latest in Newtonian innovation.


Newtonians are not only the best and most cost-effective astronomical telescopes, but they can also be used to great effect during the day! In this article, I’ll be reporting on a number of eyepieces, as well as new, roof-prism based systems that  provide correctly orientated views of the Creation. Such devices coupled to a small, portable Newtonian telescope leave traditional spotting ‘scopes in the dust.


Tune in soon to find out why…………………………..


De Fideli.

De Rerum Natura

Hubble deep Field Image. Credit: Wiki Commons.


However, the Most High does not dwell in temples made with hands, as the prophet says:

 ‘Heaven is My throne,
And earth is My footstool.
What house will you build for Me? says the Lord,
Or what is the place of My rest?
Has My hand not made all these things?’

                                                                                         Acts 7:48-50


A new paper by a team of Oxford University scientists, submitted to the Royal Society, London:

Dissolving the Fermi Paradox

(Submitted on 6 Jun 2018)

The Fermi paradox is the conflict between an expectation of a high {\em ex ante} probability of intelligent life elsewhere in the universe and the apparently lifeless universe we in fact observe. The expectation that the universe should be teeming with intelligent life is linked to models like the Drake equation, which suggest that even if the probability of intelligent life developing at a given site is small, the sheer multitude of possible sites should nonetheless yield a large number of potentially observable civilizations. We show that this conflict arises from the use of Drake-like equations, which implicitly assume certainty regarding highly uncertain parameters. We examine these parameters, incorporating models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude. This makes a stark difference. When the model is recast to represent realistic distributions of uncertainty, we find a substantial {\em ex ante} probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it. This result dissolves the Fermi paradox, and in doing so removes any need to invoke speculative mechanisms by which civilizations would inevitably fail to have observable effects upon the universe.

Full Paper here



De Fideli.

Collins Stars & Planets (5th Edition): Book Review.

The new edition ( October 2017) of a favourite observing guide.

















Collins Stars & Planets (5th Edition, October 2017)

Publisher: William Collins

Authors: Ian Ridpath & Wil Tirion

ISBN: 978 000 823927 5

Book size: 400 pages

Retail Price: £19.99 (UK)

The urge to study the sky transcends national boundaries, and so it should. The skies are open to us all.

pp 2

It’s been ten long years since I last purchased my field guide to the stars: Ian Ridpath & Wil Tirion’s 3rd edition of Stars & Planets. Travelling with me the length and breadth of the country and also on a few overseas trips, this pocket sized guide has proven indispensable for my grab and go excursions under the night sky. Alas, the wear and tear over the last decade is now definitely showing. The binding has now come loose and the pages have become heavily soiled from excessive handling. So, I figured it was high time that I got a new copy of this well received volume, and was delighted to see that it was now in its 5th edition (October 2017).

Stars & Planets is the result of a fruitful collaboration between the British amateur astronomer, Ian Ridpath, and an illustrator, Wil Tirion, living in Holland. In keeping with earlier editions, the first two thirds of the work consists of comprehensive maps of the night sky (both northern and southern hemispheres being readily presented) as they appear from month to month. In addition you will find fairly simple maps of all 88 constellations that grace the night sky, together with a list of interesting objects; some brief mythology, as well as notes on their brightest stars and deep sky objects within reach of a small backyard telescope. The full panoply of celestial objects are represented, including  a suite of pretty double stars, open clusters, emission nebulae, globular clusters, the brighter galaxies and planetary nebulae.  What particularly attracted me to the earlier edition was the relative simplicity of the maps; they were clearly designed to be used in the field where they present the basic outline of each constellation, as seen with the naked eye from a reasonably dark country sky. This enables one to easily ‘star hop’ from one object to the next. Striking a balance between adequate content and clear presentation, it is ideally suited to casual observing, adopting a low tech (my particular favourite) approach.

Each constellation shows the main deep sky objects accessible to an observer with a small, backyard telescope or binoculars.


















I was delighted to see that the latest edition retained this same format, only that the maps are now presented with noticeably better contrast against a darker blue sky background. The introduction is filled with basic but very comprehensible facts to help you make sense of how the sky ‘works,’ as well as providing excellent notes on star names (both common and the Greek lettering system), how the planets move in the sky as well as such interesting topics as precession of the equinoxes. The final one third of the book covers information on practical astronomy, including a no frills overview of telescopes and binoculars, observing double and variable stars, comets and meteorites, the Sun, and the planets, including a brief overview of sky transparency and astronomical seeing. Here you will also find a very well laid out section on lunar observing, with plainly presented maps of the particular lunar sections that can observed as it grows from a thin crescent through to full Moon.

Overall, the content is ideally suited to those having small telescopes (60mm to 100mm aperture) and binoculars, with virtually all the objects being well seen with a telescope of just 6 to 8 inches in aperture. The volume is handsomely illustrated throughout, with very high quality images of a wide variety of heavenly bodies; both in the solar system and far beyond. While these are strictly not necessary in a field guide, they certainly improve the overall attractiveness of the book. My only criticism of the work is that the binding is the same as in earlier editions, and so will surely come loose with extensive handling. It would have been better to produce this with a simple ring or sewn binding for greater durability in the field.

For busy grab ‘n’ go observers.

















Overall, I highly recommend this book as a conveniently small (for travel) but excellent field guide to the night sky that will be appreciated by either novices or seasoned observers alike. It’s strength lies with its simplicity and will keep a busy amateur happy for many years.



Neil English’s ambitious new historical work, Chronicling the Golden Age of Astronomy, will be publised later this year.



De Fideli.

Changing Culture III: Aperture & Resolution.

On the left, a 90mm apochromatic refractor and on the right, a 203mm f/6 reflector enjoying a bout of late evening sunshine.

On the left, a 90mm apochromatic refractor and on the right, a 203mm f/6 Newtonian reflector enjoying a spell of late evening sunshine.












One of the ABCs of telescopic optics is that resolving power scales linearly with aperture and light gathering power with the square of aperture. These are fundamental facts that are demonstrably true and have been used productively over two centuries of scientific applications. And yet, all the while, there has been a consistent drive in the last few decades within a section of the amateur community that somewhat erroneously links performance to absolute monetary value. This largely corrupt movement is most ostensibly seen in the refractor market, where amateurs are apparently willing to shell out relatively large sums of money for telescopes that, in terms of performance, are severely limited by their small apertures. This is a worrying trend indeed, and has led many astray within the hobby.

In this capacity, I decided to highlight the anomaly by devising a simple test which exposes this ‘peashooter’ mentality for what it is; a gross misrepresentation of basic optical principles.

Materials & Methods:

Two telescopes were set up in my back garden; a 90mm apochromatic refractor retailing at £1017 (tube assembly only) and a 203mm f/6 Dobsonian, with a retail price of £289, but with some basic modifications (97% reflectivity coatings and a smaller secondary giving a linear obstruction of just 22 per cent) which increased its cost to  approximately half that of the smaller telescope. The Newtonian was carefully collimated before use.

The telescopes were left out in the open air during a dry and bright evening when the temperatures had stabilised and were fully acclimated. Both instruments were kept out of direct sunlight. The refractor had an extendable dew shield to cut down on ambient glare, while the Newtonian was fitted with a flexible dew shield to serve the same purpose. To remove the complicating effects of atmospheric seeing, the telescopes were targeted on the leaves of the topmost boughs of a horse chestnut tree, located about 100 yards away.

Both telescopes were charged with approximately the same magnifications, in this case, a very high power was deliberately chosen; 320x. Next, the images of the leaves were examined visually, being especially careful to achieve the best possible focus, and the results noted.


The 203mm Newtonian images of the leaves were crisp, bright and full of high contrast detail. In comparison, the image served up by the refractor was much dimmer and a great deal of fine detail seen in the larger instrument was either ill-discerned or completely invisible in the smaller instrument. Though less dramatic, the same results were obtained when a larger refractor (127mm f/12) was compared with the 203mm f/6 Newtonian under similar conditions, with the latter delivering brighter, crisper images with finer detail.


This simple experiment, requiring nothing more than a few minutes of one’s time and no complicated formulae or optical testing devices, clearly showed the considerable benefits of larger aperture. The images served up by the Newtonian were brighter and easier to see than those served up by the smaller instrument. Resolving power and light gathering power work hand in hand; you need decent light grasp to discern fine details and vice versa.These results were largely independent of the surrounding atmospheric conditions, as the targets were located at close proximity to the telescopes and thus had to travel through a short column of air.

These experiments were repeated with larger instruments; a 127mm f/12 refractor and the same 203mm Newtonian, with the same results, that is, the smaller instrument runs out of light faster than the larger and shows less fine detail in the images served up.

These results confirm that larger aperture is superior to smaller aperture. No amount of claptrap can change the result either. Complications may arise when the same tests are performed on celestial targets, especially during bouts of turbulent atmospheric seeing, when the larger instrument will be commensurately more sensitive. In such instances, it is the environment that introduces anomalies. But when conditions are good, the benefits of larger aperture will be seen, clearly and unambiguously. Absolute monetary value has little or nothing to do with the end result, in direct contradistinction to what is claimed by those who promote small aperture refractors in an unscientific way.

See here for further reading.


De Fideli

Changing Culture.

Octavius: instrument of change.

Octavius: instrument of change.















As  I have commented on in previous communications, an urban myth has been cultivated over the years regarding the unsuitability of Newtonian reflectors in the pursuit of double stars. In the last six months or so, there are encouraging signs that more people are bucking this trend using Newtonian optics of various f ratios and in the examination of pairs of various difficulty, including the sub-arc second realm;

Exhibit A

Exhibit B

Exhibit C

Exhibit D

Exhibit E

These are but a few examples, and I can only hope that the changes will continue so that more people can enjoy this wonderful pass-time.

De Fideli

Origins of Life: A Closer Look Part I

Some life scientists believe they can present a truly naturalistic scheme of events for the origin of life from simple chemical substrates, without any appeal to an intelligent agency.

Here is one such scenario, presented by Harvard professor, Jack Szostak.

I invite you to study the video at your leisure.

In this work, I wish to critically appraise each of the steps Dr. Szostak presents in light of the latest research findings that show that any such scheme of events is physio-chemically untenable from a purely naturalistic perspective.


Video Clock Time 00.00 -10.00 min

Here Dr. Szostak sets the scene for this thesis, exploring the varied landscapes and environments under which we find life on Earth. Dr. Szostak reasonably suggests that when life first appeared on Earth, it must have done so in an extreme environment with higher temperatures and in aqueous environments with extreme pH values and high salinity. What Dr. Szostak does not acknowledge is that life was already complex when the Hadean environment first cooled enough to permit life to gain a footing. For example, there is solid isotopic evidence that the complex biochemical process of nitrogen fixation was already in place at least 3.2 Gyr ago and possibly earlier still.


Eva E. Stüeken et al., “Isotopic Evidence for Biological Nitrogen Fixation by Molybdenum-Nitrogenase from 3.2 Gyr,” Nature, published online February 16, 2015,
“Ancient Rocks Show Life Could Have Flourished on Earth 3.2 Billion Years Ago,” ScienceDaily, published online February 16, 2015,

In a more recent study conducted by a team of scientists headed by Professor Von Karnkendonk, based at the University of South Wales, solid evidence for complex microbial ecosystems in the form of stromatolite colonies were established some 500 million years earlier at 3.7 Gyr ago.


M..J Van Krankendonk et al, Rapid Emergence of Life shown by the Discovery of 3,700 Million Year Old Microbial Structures, Nature Vol 537, pp 535 to 537, (2016).

Dr. Szostak claims the origin of life must have occurred via a Darwinian evolutionary mechanism, but the self-evident complexity of the first life forms strongly argues against this assertion, as there would not have been enough time to have done so. In other words, the window of time available for the emergence of the first forms of life on Earth is too narrow to entertain any viable Darwinian mechanism.

Dr Szostak continues by considering the vast real estate available for potential extraterrestrial life forms. Szostak presents the emerging picture; the principle of plenitude – that of a Universe teeming with planets. That is undoubtedly the case; there are likely countless trillions of terrestrial planets in the Universe.  However, new research on the frequency of gamma ray bursts (GRB) in galaxies suggests that such violent events would greatly hamper any hypothetical chemical evolutionary scenario. In December 2014, a paper in Physical Review Letters, a group of scientists estimated that only 10 per cent of galaxies could harbour life and that there would be a 95 per cent chance of a lethal GRB occurring within 4 kiloparsecs of the Galactic centre, and the likelihood would only drop below 50 per cent at 10 kiloparsecs from a typical spiral galaxy. What is more, since the frequency of GRBs increases rapidly as we look back into cosmic time, the same team estimated that all galaxies with redshifts >0.5 would very likely be sterilised. These data greatly reduce the probability that a planet could engage in prebiotic chemistry for long enough to produce anything viable.


In addition to GRB induced sterilization events, Dr Szostak completely ignores the remarkable fine tuning that is required to produce a planetary system that could sustain life for any length of time.


Dr. Szostak entertains the possibility that lifeforms with fundamentally different chemistry may evolve and that our type of life might be the exception rather than the rule. This reasoning is flawed however, as the latest research suggests that carbon-based chemistry in a water-based solvent is overwhelmingly more likely to sustain any biochemical system throughout the Universe. Ammonia has been suggested as an alternative solvent to water but there are some(possibly insurmountable) issues with it.


Summary: Dr Szostak’s introduction presents a gross oversimplification of the true likelihood of prebiotic chemistry becoming established on Earth and other planets. Szostak does concede that our planet could be unique but is unlikely to be. The emerging scientific data however supports the view that life will be rare or unique to the Earth.

Video Clock Time; 10:00 – 32:00 min
The RNA World
In this section, Dr. Szostak presents the central dogma of molecular biology: DNA begat RNA and RNA begat proteins. Origin of life researchers were completely in the dark about how this scheme of events came into being, but in the mid-1980s, Thomas Cech et al discovered that RNA molecules could act catalytically.
Zaug, A. J & Cech, T. The Intervening Sequence of RNA of Tetrahymena is an Enzyme, Science, 231, (1986).

This immediately suggested a way forward; perhaps RNA was the first genetic material and over the aeons, it gradually gave up these activities to its more stable cousin, DNA. Szostak gives some examples of how this ‘fossil RNA’ has been incorporated into structures like ribosomes, the molecular machines that carry out the synthesis of polypeptide chains. His interpretation of these examples as ‘fossils’ is entirely speculative, however.

Szostak then explores hypothetical loci where prebiotic synthesis of biomolecules could have taken place, including the atmosphere, at hydrothermal vents and on mineral surfaces. For the sake of clarity, let’s take a closer look at RNA nucleotides, and in particular, the pentose sugar, ribose. Dr. Szostak mentions the Urey-Miller experiments where supposed prebiotic molecules were produced when an electric discharge was passed through a reducing atmosphere including water vapour. Though widely cited in college textbooks, its validity has in fact, long been discounted by serious researchers in the field. Urey and Miller assumed the atmosphere to be reducing in nature, but it is now known that it was neutral, consisting of nitrogen, carbon dioxide, carbon monoxide and water vapour.

The Early Setting of Prebiotic Evolution, Shang,.S
From Early Life on Earth, Nobel Symposium No. 84, Bengtson, S. (ed.), pp 10-23, Columbia University Press (1994).


Even in the complete absence of molecular oxygen, this atmosphere could not have sustained the production of prebiotic molecules, including ribose. Only in the presence of significant quantities of molecular hydrogen has some synthesis been demonstrated.

Schlesinger, G, & Miller, S. Prebiotic synthesis in Atmospheres containing methane, carbon monoxide and carbon dioxide. Journal of Molecular Evolution, 19, 376-82 (1983).

The problem with this scenario though is that molecular hydrogen would rapidly escape from the Earth’s gravitational field and thus is entirely irrelevant to the question of prebiotic synthesis.

An Aside:

Video Clock Time: 20:00 min: The Narrow Time Window:  Reconciling Dr. Szostak’s timeline for prebiotic chemical evolution with impactor bombardment history.

At 20.00min on his video, Professor Szostak envisages the time during which prebiotic chemical evolution took place on the primitive Earth. He dates it to a period between 4.2 and 3.8Gyr ago (the supposed time of the beginning of the RNA world). Szostak presents a warm, aqueous environment during which all these reactions were taking place. But the planetary scientists modelling the impact history of the inner solar system have revealed a violent early history for the Earth. Extensive isotope analysis of terrestrial and lunar rocks, as well as cratering rate analysis indicate that the inner solar system was subjected to intense bombardment from the debris left over from the formation of the planets, which occurred between 4.5 and 3.9 Gyr ago. The cratering intensity declined exponentially throughout that era, except for a brief episode of increased bombardment between 4.1 and 3.8 Gyr ago. This is known as the Late Heavy Bombardment. One study has estimated that the total accumulation of extraterrestrial material on Earth’s surface during this epoch added a mean mass of 200 tons per square yard over all the surface of the Earth. Thus, Dr. Szostak’s relatively ‘gentle’ scenario is untenable. Realistically, the only oceans to speak of during this epoch are those of magma.


Anbar A.D. et al, Extraterrestrial Iridium, Sediment Accumulation and the Habitability of the Earth’s Surface, Journal of Geophysical Research 106 ( 2001) 3219-36.

Back to Ribose (a key component of RNA nucleotides discussed by Dr. Szostak). The only plausible mechanism for the synthesis of ribose is the so-called Butlerow reaction (also referred to as the formose reaction) which involves the coupling of the single carbon molecule, formaldehyde (methanal) in spark-ignited reactions, forming sugars of varying carbon numbers, including ribose. However, many side reactions dominate formose chemistry, with the result that the atom economy with respect to ribose is very low; up to 40 other chemical products being typically produced. This is the case in carefully controlled laboratory synthesis (read intelligently designed!), where the reaction is protected from contamination. Experimentally though, the presence of small amounts of ammonia and simple amines (which should be permissible in Szostak’s scheme) react with methanal to bring the formose reaction to a grinding halt.

Chyba, C. & Sagan,C., Endogenous Production, Exogenous delivery and Impact Shock Synthesis of Organic Molecules: An Inventory for the Origins of Life, Nature 355(1992): 125-32.

The concentrations of ribose would have been far too low to sanction any RNA world envisaged by Dr. Szostak. Compounding this is the added problem that ribose and other simple sugars are subject to oxidation under alkaline and acidic conditions, and since Szostak presents both hot and cold scenarios on the primitive Earth, it is noteworthy that ribose has a half life of only 73 minutes at 100C (near hydrothermal vents) and just 44 years at 0C.


Oro, J., Early Chemical Changes in Origin of Life, from Early Life on Earth, Nobel Symposium No. 84, Bengtson, S. (ed.), pp 49-50, Columbia University Press (1994).

But there are more serious reasons why Szostak’s scheme of events could ever have happened on the primitive Earth. This is encapsulated in the so-called Oxygen-Ultraviolet Paradox.
Szostak envisages prebiotic synthesis in warm aqueous environments, but on the primordial Earth, some 3-4 Gyr ago, the presence of much higher levels of radionuclides such as uranium, thorium and potassium-40 would have presented another proverbial spanner in the works. These would have been more or less evenly distributed over the primitive Earth and when the radiation they emit passes though water, it causes its breakdown into molecular oxygen, hydrogen peroxide and other reactive oxygen species. Oxygen and the associated reactive oxygen species easily and quickly destroy organic molecules; not just ribose and other sugars, but the other biomolecules mentioned by Dr. Szostak too, including fatty acids and purine & pyrimidine bases required for the production of micelles(see Part II) and nucleotides, respectively .

The other part of the paradox pertains to the produce of stratospheric ozone, which requires ultraviolet light. The ozone layer was not present during the epoch in which Szostak’s scheme of events would have occurred. The intense UV irradiance on the primitive Earth would have sundered any exposed prebiotics, further compounding the problem.


Draganic, I.G., Oxygen and Oxidizing Free Radicals in the Hydrosphere of the Earth, Book of Abstracts, ISSOL , 34 (1999) .

Draganic, I, Negron-Mendoza & Vujosevis, S.I, Reduction Chemistry of Water in Chemical Evolution Exploration, Book of Abstracts ISSOL, 139 (2002).

Dr. Szostak appears to be completely unaware of Draganic’s work (though citing Hazen and Deamer’s hydrothermal synthesis work @ 31 minutes) and indeed, in and of itself, would preclude any further discussions of his scheme of events. But we shall nonetheless persevere with this analysis.


This work will be continued in a new post (Part II) here.

The Life & Work of Dr. William Doberck (1852-1941)

The Makree refractor erected in Hong Kong.

The 13.3 inch Markree refractor erected in Hong Kong.

It gives me great pleasure to present an essay written by my compatriot, Dr. Kevin MacKeown (now at the Unversity of Hong Kong) on the life and work of the Danish astronomer, Dr. William Doberck (1852-1941), who, amongst other things, dedicated his professional career to double star astrometry.

Dr. William Doberck ( 1852-1951).

Dr. William Doberck ( 1852-1941).

Most significant for me was his spell at Markree Observatory, Co. Sligo, Ireland (my homeland), where he used a magnificent 13.3 inch refractor, with a lens fashioned by Robert A. Cauchoix of Paris, which was privately owned by a wealthy British gentleman, Edward J. Cooper. There the telescope was used to catalog 60,000 stars. After leaving the west of Ireland, Doberck moved the telescope to Hong Kong Observatory, where he served as its first director between 1883 and 1907.

You can view this essay here.


Neil English is working on a new book – Tales from the Golden Age – honouring the life and work of the greatest telescopic observers in history.

De Fideli.

Charm Offensive: A Spyglass Comes This Way!

A telescope that fits in the palm of your hand.

A telescope that fits in the palm of your hand.














Whichever way you slice it, the invention of the telescope revolutionised human civilization and extended our reach far into the wider Universe. And though the telescopes of the 17th century were very crude and unwieldy by today’s standards, the arrival of the achromatic doublet greatly increased their convenience and ease of use. The new technology, patented first by John Dollond in 1758, was quickly exploited to produce portable instruments for the military and the navy in the form of the nautical or ‘signalling’ telescope. And while Dollond & Co. made a fortune selling these telescopes to customers all over the British Empire and beyond, it was not long before an army of other opticians took their cut of the market, by fashioning their own renditions of the instrument.

An un-coated object glass of one inch aperture.

An un-coated object glass of one inch aperture.














As a result, although many authentic signalling telescopes built by the finest opticians in Europe and the New World can still be had for prices that reflect their provenance in the 21st century, many other antique models fashioned by more obscure artisans can be purchased relatively cheaply even in today’s market.

I’m no antique collector though, but I was pleasantly surprised to see that the classical spyglass, the signalling telescopes of old, are still being made today. I took delivery of one such instrument this very afternoon. Tipping the scales at about 380 grams, the telescope collapses to just half a foot (15 cm), making it fit snugly in your pocket, and extends to 15 inches – in three draws – when pressed into service.

An ornate eye lens.

An ornate eye lens.





It was only in the aftermath of World War II that anti-reflection technology in the form of a thin layer of magnesium fluoride was first applied to lenses to increase light throughput and decrease glare, but the ship telescopes that accompanied the soldiers and sailors of the 18th and 19th century were entirely un-coated.

In this capacity, though some of my contemporaries might baulk at the thought, I was actually delighted to see that the lenses in my ‘Ship Telescope’ were also un-coated and thus more consistent with those from antiquity. The instrument  has an objective of one inch (26mm) aperture and delivers a correctly orientated image with a power of 6 diameters. Objects can be focused from infinity to just a few feet away! Focusing is intuitive, achieved by slowly sliding the draw-tube in and out, as appropriate.Optically, the instrument isn’t great – compared to all the wonderful and inexpensive mass produced telescopes we enjoy now – but I believe it is more or less typical of what these instruments could deliver in their day. Specifically, it displays strong field curvature, some obvious lateral colour, minor internal reflections when turned on very bight objects, as well as moderate spherical aberration in a very narrow field of view. But to dismiss the instrument as optically shoddy is to completely miss the point! The centre of the field is good and sharp and perfectly adequate to the task intended for it. And what it lacks optically, it more than makes up for in other ways.

The three-draw spy glass extends to about 15 inches.

The three-draw spy glass extends to about 15 inches.

Although my model only set me back about £35 (inclusive of delivery), I was pleasantly surprised by the build quality of the instrument. The main tube has a stitched leather sheath and the three draw tube is entirely fashioned of polished brass. Each draw glides smoothly over the other with just the right amount of traction. Handling the instrument for any length of time imparts the strong aroma of cuprum et pellis in the palm of one’s hand that is so reminiscent of bona fide antique pieces. It also came with a nicely machined brass dust cap for the objective, though without a soft case or box to store it in.

I spent the odd idle moment enjoying the landscape around my home with the instrument and once my boys arrived back from school, they were eager to try out the new pirate ‘scope for themselves. All in all it was a big hit with the entire family and just a joy to use on a bright Spring day. A telescope like this would make a thoughtful and relatively inexpensive gift for someone who would like to see the world through the eyes of a child once again. It will bring you all the way back to the time of your youth, when the world seemed more innocent than it is today; an ornate and charming memento of a by gone age.

Oscar keeps a close eye on those roosting corbies.

Oscar keeps a close eye on those roosting corbies.














De Fideli

A New Filter for Planetary Observers

The Televue Bandmate Planetary Filter.

The Televue Bandmate Planetary Filter.

Planetary filters have been around for a long time. For many years simple, dyed in glass colour filters were used productively by keen observers of the bright planets Mars, Jupiter and Saturn. In general, the would-be observer would choose a filter with a colour opposite to that of the feature he/she wished to observe. And while these filters are still used productively by seasoned observers today, in recent years a new type of filter has come to the fore; the interference filter; designed to selectively block unwanted wavelengths and transmit selected wavelengths with high efficiency.

The interference filter is made out of successive layers of dielectric materials, with thicknesses ranging between one-quarter and one-half of the target wavelength. The coatings are deposited onto an optically flat glass surface in a vacuum using ion beam sputtering technology. The unwanted wavelengths are nulled by the reflections generated by the dielectric materials, which undergo destructive interference and thus are removed from the optical path. Because the designer can cut off and enhance any visible wavelength or waveband at will, they offer the potential to experiment in new ways with the human visual system.

A good planetary filter ought to accomplish a number of things.

1. Glare reduction, which almost invariably leads to an increase in perceived image quality.

2. Exaggerating differences in brightness between the various coloured features of a planetary image.

3. Overcoming to a greater or lesser degree, the image distorting effects of the atmosphere

3. Enabling observers to study different levels of a planetary atmosphere.

4. Enhancing the resolving power of a telescope.

In the last few years, Televue has brought to market a series of interference based filters designed to enhance details on the bright, extended objects like planets. Their latest product, the Bandmate Planetary (BPL) Filter, has different dielectric layers applied to each side of the optically flat BK7 substrate. At the present time, Televue only produce the filter in a 1.25 inch format, which is threaded to mate to most any eyepiece. Some have questioned why not a 2 inch version? I believe the company reasoned (correctly) that most planetary eyepieces are going to be of the smaller, 1.25 inch variety. When viewed in bright daylight, the filter gives a pinkish tinge to objects and seems to enhance brown, yellow and red tones.

Overall, the light transmission of the filter is good. Comparing it with a light yellow colour filter, a Baader Fringe Killer and the Baader Contrast Booster, the Televue BPL showed less light transmission than the all of them bar the Contrast Booster. Light transmission is important in determining the size of a telescope that would benefit from its use. If the telescope is too small and gathers only a limited amount of light, the filter will dim the image too much. For this reason, the benefits of filters are best revealed in larger aperture instruments.

I tested the filter on a number of telescopes, with apertures ranging from 80mm to 200mm My target was invariably the bright planet Jupiter, now well placed in the sky for observation. In my 80mm f/5 achromat, the filter imparted a reddish tone to the planet. Visible chromatic aberration was reduced but the image was quite dim, making any gains in contrast marginal at best.

When tested with a 5 inch refractor, the effects of the Televue BPL were more readily observed. The greater light gathering power of the instrument allowed the filter to transmit a decent amount of light to the eye. The modest amount of secondary spectrum seen in the unfiltered image was effectively removed with the filter and the elaborate banding of the giant plant was more easily seen. Close examination of the image under optimal magnifications revealed many shades of orange, yellow, fawn and dark brown. The Great Red Spot (GRS) was much easier to see with this filter than without it. The bright zones surrounding the belts came through in a plain white.

When I tested the filter on a 17cm f/16 Maksutov Cassegrain and a 8-inch f/6 Newtonian, its effects were most effectively manifested. Like all good filters, it reduced glare and greatly enhanced the dark Jovian belts. Under the best conditions, the filter brought out very subtle features, such as ovals and festoons in the planet’s southern hemisphere. The GRS was very obvious and with appropriate magnification, some substructure could be seen within it. Shadings in the polar hoods were also more easily seen with the filter.

When compared to other filters with a proven track record to enhance certain Jovian features, the Televue BPL edged ahead in terms of the amount of Jovian atmospheric details revealed. All in all, the images struck a nice balance between image brightness and the telescope’s contrast transfer.

The fact that the filter passes longer wavelengths better than shorter wavelengths may help stabilise the image. This is because of Rayleigh scattering which predicts that for a given sized particle, light is scattered in inverse proportion to the fourth power of wavelength. This means that the air is less turbulent when viewed at longer wavelengths. This effect was not vigorously tested however.

Cui bono?
What is clear from my tests is that the Televue BPL filter works very well indeed for larger aperture ‘scopes. Personally, I would not recommend it for ‘scopes less than about 5 inches in aperture but will work brilliantly with larger Dobsonians and catadioptric telescopes. It will also work extremely well in suppressing the chromatic aberration of inherent to larger achromatic telescopes and would thus be a useful tool used with old fashioned classical refractors housed in observatories up and down the country.

Planetary imagers will also likely benefit from using this filter, especially large aperture instruments. Because of its reduced light transmission, slightly longer exposures may be necessary in order to achieve optimal results.


In summary, the Televue BPL filter is an excellent filter to divine as much detail from Jupiter’s massive and ever changing atmosphere as is conceivably possible. If you’ve never seen the Great Red Spot, you will with this filter! Saturn and Mars should also benefit from its use. It is more expensive than other filters on the market but I believe the extra cost incurred is well worth it when you see what the filter can achieve. Albert Nagler has definitely done his homework with this exciting new product. Highly recommended!

ergo dixi vobis

Typical UK Retail Price: £113.

Typical US Retail Price: $140.

De Fideli

Neil English is author of Choosing and Using a Dobsonian Telescope.