Tele Vue has
enjoyed great success throughout the United States as producers of
high quality optical products for the discriminating visual observer
and more recently for the advanced astro-imager. Even after 30 years,
Tele Vue eyepieces are made to a standard by which all other designs
are compared and are deservedly the acknowledged world leaders in
this arena of visual observing. But, if we’re honest, their
telescopes haven’t enjoyed the same universal acclaim that say
Astro Physics or Takahashi has enjoyed. Yes, they are very popular in
the US, but here in the UK they enjoy a love-hate relationship with
amateur astronomers. Some folk adore them. Other’s think they
are too expensive and over-rated.
As a case in
point, my path crossed with Anthony McEwan, a discriminating visual
observer who once owned a lovely Tele Vue 85 and used it on most
clear nights near his home on the Murray Firth in North East
Scotland. But after experiencing the views through an economy-priced
Sky Watcher ED 80, he told me he was unable to justify keeping the
considerably more expensive Tele Vue, as the ED 80 was serving up
very comparable images. McEwan’s story is not unique. My own
experiences with a Tele Vue 102 were that, while it is mechanically
in a different league to cheaper ED doublets, there was little
difference between the views they delivered. No if or buts about it.
That said,
owning a Tele Vue refractor is special. For me, they strike a near
perfect balance between form and function, exuding quality from the
tip of their threaded lens cells to the exquisite engineering of
their rack and pinion focusers. And if looked after, they can last
several lifetimes. So even though the Tele Vue 102 didn’t tick
all the boxes for me, I still hankered after a high quality,
uncompromising refractor for use by day and night; an instrument that
I could take anywhere at a moment’s notice and which could
deliver the readies when called for. The 102 is simply too big to be
considered a grab and go scope, so when a used Tele Vue 76 came up
for sale at a reasonable price I took a chance and purchased it. I
now know I made the right decision, as it really has exceeded all my
expectations.
The TV 76
goes anywhere at a moment’s notice
Introduced
in 2001, the Tele Vue (TV) 76 was the replacement for their older ED
scopes – the Ranger and Pronto – both of which were
splendid 70mm F/7 doublets with good but not Apo quality colour
correction. The TV 76 (F/6.3) has a slightly larger aperture but the
same focal length as the older scopes. Like the Tele Vue Pronto, it
has a beautiful rack and pinion focuser in a 2-inch format. Bought
new, the package includes a custom soft case, a screw-on lens cover
and sliding dew shield, a 20mm Tele Vue Plossl eyepiece, and 2-inch
Everbrite diagonal, 1 ¼" adapter (all with clamp ring
fittings) and manual signed by Uncle Al himself. When outfitted with
an eyepiece and diagonal, it tips the scale at just over six pounds.
That’s significantly heavier than some top-of the range
spotting scopes but not enough in my opinion to present problems in
the field. Any loss of portability though is made up for by the TV
76’s amazing versatility. A three inch aperture is just about
large enough to make high resolution visual observing worthwhile, and
its short focal length (480mm) coupled to a big, wide angled eyepiece
means that you get majestic, five-degree views of the night sky.
I received a
forest green, pre-2005 model, as it has the chromed focus barrel and
single focus lock screw located just above the focus wheels.
Personally, I’ve always preferred the look of the older focuser
to the newer version. It also came with a balancing adaptor that
enables you to adjust the pivoting point of the scope quickly and
effectively when using eyepieces and other accessories that vary in
weight.
It’s
easy to test good optics and you don’t need an optical test
bench to do it. The optics on this scope must really be experienced
to be believed. Having owned and looked through several lower-cost ED
doublets of similar specification, I can say, hand on heart, that the
TV 76 bested them all. The difference was more dramatic in my
opinion, than those I had experienced in comparing the 4-inch TV 102
with the Orion/Sky Watcher 100ED. Star testing this scope at 120x
shows how superbly crafted the optics are. Vega displays a bone white
Airy disk surrounded by a single diffraction ring. No colour error
was noted, safe for the occasional sparkle from atmospheric
turbulence. The diffraction patterns both inside and outside focus
were the nearest I’ve seen to perfection in any
telescope. They’re cleaner and easier to see compared to the
slightly fuzzier patterns I’d usually observe with cheaper ED
doublets. Like other two-element Apos, it does display a small amount
of colour on the rim of the diffraction pattern both inside (magenta)
and outside (green) focus but that’s normal behaviour for an
instrument with an ED doublet objective.
The
diminutive TV 76 atop a sturdy Gibraltar Alt-azimuth mount
The very well figured doublet objective of the TV 76
If you look carefully at the objective at various angles, you’ll
notice that not all the air to glass surfaces have the same
anti-reflection coatings applied. The coatings seem to be
individually tuned to maximise light transmission. Although I think
knife edge baffles do a slightly better job, stray light is
effectively dealt with using the company’s matt black flocking
material. The TV 76 comes with a dedicated clamshell and mounting
bracket that enables you to attach the instrument to a Gibraltar or
Telepod mount using two wing knobs. You can also attach it to a
heavy-duty photographic tripod for more portable terrestrial
projects.
Using a Vernier callipers I measured the colour error (see my
previous Cloudy Nights article, “A little piece of Russian
magic” for details) of this scope to be about 0.018% which I
believe to be very good considering it has such a short focal ratio
(F/6.3). A well figured lens ought to able to take very high
magnifications before noticeable image breakdown occurs. My daylight
and night time tests with high quality eyepieces and image amplifiers
show that the TV 76 can take amazingly high powers and I can
confidently attest that this little scope can hold 100x per inch of
aperture. It has very low spherical aberration (at least 1/8th
wave measured) and is devoid of astigmatism and coma. I consider that
extraordinary too. And it’s no accident either. It’s down
to both the excellent figure of the lens and the employment of a
large air gap between the objective elements. Nagler is clearly a fan
of the late American astronomer James Gilbert Baker (1914-2005), who
introduced large air spaces between the objective elements in order
to reduce spherochromatism (the change of spherical correction with
wavelength) in the design of his refractors. And Uncle Al’s
been doing it for quite some time now. My old 1991 Genesis F/5 had an
air gap measured in inches between the front doublet elements!
The superlative rack and pinion focuser on the TV 76
One for the Birds
I must admit, though I’m no birder, I look through scopes as
frequently by day as by night. The great advantage of using a
‘cross-over scope’ like the TV 76 compared with a
conventional spotting scope, is that it can be purchased as an
optical tube assemby and you can carefully choose a diagonal and
eyepiece combination tailored to your needs. This, in my opinion,
makes them far more versatile than dedicated spotting scopes. One can
choose either a 1.25 inch diagonal or a 2-inch diagonal depending on
the eyepiece you want to use. Most birders make do with spotting
scopes that use relatively lightweight 1.25-inch eyepieces. 2-inch
eyepieces deliver greater fields of view, which is great for
astronomy but normally overkill if you’re trying to concentrate
on the variegated feathers of a nesting kestrel. Besides, 2-inch
eyepieces add a lot of weight to the scope too.
By purchasing an optical tube assembly, you get to choose the
kind of viewing you want to experience. Having observed
through traditional spotting scopes for many years, with their
dedicated, non-interchangeable zoom eyepieces, I find the freedom the
TV 76 gives me to be a great liberation. If for example, you wish to
experience the prismatic world with its correctly orientated view, a
number of companies including William Optics produce both 1.25 and
2-inch prismatic diagonals angled for 45 degree viewing. They were
designed to give very good images over typical daylight
magnifications for their small ED scopes. Alternatively, you can
purchase the 60-degree Everbrite diagonal for 1.25 inch eyepieces
which delivers the finest views this instrument can offer -although
you’ll still have to get used to left-right reversed images!
The Tele Vue 60 degree Everbrite Diagonal
Nocturnal Adventures
Night time observing shows up many of the strengths and a few of the
weaknesses of this scope. With a 31mm Nagler, the little refractor
serves up five degree views more comparable to giant binoculars than
to an astronomical telescope. Many economical eyepieces work well
with its modest focal ratio, especially orthoscopics. I noted some
field curvature when used with low power eyepieces of various genres
(including plossls, Pentax XWs and Naglers). Stars sharply focused at
the centre have to be slightly re-focused at the edge of the field.
Little or no field curvature was detected using my high power
eyepieces.
The Moon and bright planets are gorgeous through this instrument.
Creamy Jupiter showed me four or five bands on good nights with a
palid Great Red Spot and hints of low contrast swirls and ovals in
the giant planet’s atmosphere. The four ‘Medicean stars’
resolve to tiny globes at 196x. Banding on the Saturnian globe was
also evident at powers at 120x and above but the rings were too
‘edge-on’ for me to test this scope on them. The full
Moon was sharp and colour free with the prominent rays craters
clearly in evidence. The background sky showed up the pinpoint light
of faint stars near the limb – all good signs that stray light
was being kept at bay. First quarter luna is a sight for sore eyes at
powers up to and in excess of 200x with no colour fringing evident
near crater rims. I did note that, while observing our satellite at
high powers, the lunar regolith seemed to be imparted with a very
pale ‘coffee’ coloured hue compared to the view served up
by a Newtonian reflector set up next to it.
The TV 76 really rocks when it comes to resolving double stars. The
instrument’s excellent colour correction makes seeking out
variegated doubles a joyous adventure. Albireo, 61 Cygni and Almach
unveil their austere beauty at moderate and high powers. Forget
Polaris and Rigel: these high-contrast companions usually cited as
tests for a 3-inch refractor are too easy for this refractor. More
challenging (and more fun) are the lovely triple system of Iota
Cassiopeiae, and close binaries such as delta Cygni and epsilon
Aurigae, all of which the TV 76 managed to resolve. And though it’s
not the hardest binary system to discern with a good 3-inch
refractor, Epsilon Bootes (Izar) is arguably one of the most
compelling sights to see in a small telescope in all the heavens.
Steady skies and high
magnifications are required to elucidate its lovely secret; a
magnitude +4.6 blue green companion
separated from its primary by just 2.9 arc seconds of sky. Now my
little telescope can resolve
pairs as close as 1.5 arc seconds provided they are of fairly
equal brightness. But the near
sevenfold difference in
brilliance between Izar and its main sequence companion renders the
secondary hard to see, overwhelmed as it is by the light of its
primary. Optics plays a role with this system too – I've looked
through 4-inch instruments that consistently struggled with this
system but a high quality 60mm refractor should just do the job under
good conditions. And though I've looked at Izar with all sorts of
telescopes, from small portable 'scopes to humongous Dobs measuring
fully two feet across, I must say that the fondest view of Izar I've
ever enjoyed was with this 3-inch refractor. During a recent vacation
to a tiny coastal resort on the north west coast of Scotland, I
chanced upon some fair weather. Tucked away in a shallow inlet, the
early evening winds subsided gradually to a dead calm after midnight,
allowing me to take advantage of exceptional observing conditions
with dark magnitude +6.5 skies. On two successive nights, I was able
to rack up the power on my 'scope to 276x to get a razor sharp
separation of the system. Like a budding yeast cell seen under a
microscope, the pale blue ball of the secondary sat on an otherwise
perfect first diffraction ring of a golden orange primary. Small
wonder the famous double star observer Otto Struve was impelled to
call it Pulcherimma!
The Tele Vue 76 waits patiently for darkness at a remote Scottish
resort.
The TV 76 is arguably among the most perfectly made, ultra-compact,
and highly versatile refracting telescopes ever designed. And even
though many other instruments of similar specification to the TV 76
are now available at much lower cost than what this instrument
retails for ($1725), I believe an experienced observer will notice
the difference even during casual viewing, either by day or by night.
While being an excellent astronomical instrument (with limited
aperture of course), it also provides a real alternative to birders
and other nature enthusists who require a super-quality, durable,
no-nonsense instrument that will deliver bright, high contrast images
and with better colour correction than any traditional spotting scope
can currently deliver. Uncle Al has really done his homework with
this instrument and, not having looked through a Tele Vue 85, I
consider it to be the real jewel in Tele Vue’s telescopic
crown.
The author has no affiliation, commercial or otherwise with Tele
Vue Optics.
You can hear more about my telescopic musings in his forthcoming
book, Choosing and Using a Refracting Telescope,
which will be published by Springer in 2010.
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