IN THE SHOPSTeleVue Delos:
Spectacle wearers often struggle with the poor eye relief on eyepieces, but the new Delos
range from TeleVue promises to change that, and offer a wide-field too, says Neil English.

W The first, and still the most popular, trio of TeleVue Delos eyepieces. Image: Neil English.

come to expect from TeleVue. They all possess anadjustable eyecup that enables the observer to findthe optimum distance between the large field lensand the eye. I found this activity to be relatively
easy to do consistently. All that is required is a little
adjusting of the position of the twist-up sleeve until
you can see the entire field of view without blackouts.
I found that performing these adjustments during
daylight to be the best way forward. Examining
the field stop under a bright light showed it was
devoid of dust. The multi-coatings applied to thelenses are amongst the best I’ve seen. All in all,these eyepieces are exceptionally well designed.

Notes from the fieldConsult any decent bookon practical amateur
astronomy and you’llsoon uncover recommendations
on the best eyepieces to use withyour telescope. If the native focal
ratio of the telescope is high (sayf/10 or beyond), pretty muchany modern eyepiece design
works well to deliver sharp, highcontrast images with little in theway of aberrations such as coma,
astigmatism, field curvature andso on. Place the same inexpensive
ocular in an f/6 telescope, though,and the limitations of the design
soon become apparent. Stars at
the centre of the field are sharp
and well defined but as one moves
off axis, the pinpoint star images
become more and more distorted,
necessitating higher quality
designs that can correct for these
distortional effects.
The same is true when one
explores the traditional wisdom
on planetary eyepieces. Highquality orthoscopics and Plössls
are usually recommended owing to
the low number of glass elements
and excellent light throughput.
However these tried and trusted
designs, while delivering excellent
images, suffer from a rather
restrictive field-of-view and exhibit
76 | Astronomy Now | April 2013poor eye relief, making it very
difficult for observers who wear
spectacles from engaging with theentire telescopic field.
Nowadays, you can have yourcake and eat it. TeleVue Optics of
New York have introduced a newline of oculars that combine allthese features in one package: enter
the Delos. Named in honour ofPaul Dellecchiale, TeleVue’s senior
optician, each eyepiece in the range
offers a full 20mm of eye relief andan immersive 72-degree apparent
field-of-view.

Fit and finish
I received three Delos eyepieces
for field testing; the original focal
lengths in the range – 17.3mm,10mm and 6mm. All have a very
solid feel with the exceptional
quality construction that you’dI tested all three oculars on a variety of telescopes
ranging from 750mm to 1,200mm focal length.
They all were able to reach focus. None ofthe eyepieces were parfocal, though the 6mmand 10mm models were almost so, while the
17.3mm required considerably more back focus
in comparison to the others. All three eyepieces
delivered excellent images with beautiful contrast
across the field-of-view. The field stop is very welldefined and shows a bright blue ring in daylighttests, which was not seen in my orthoscopics. Icould not detect any lateral colour in the images.
My tests were conducted on some prominent
star clusters, such as the Pleiades Cluster (M45) anda first quarter Moon, searching for signs of off-axis
astigmatism, field curvature, flaring and light scatter.
In more detailed tests I conducted a side-by-side
comparison of the 6mm Delos with a tried and trusted
6mm orthoscopic eyepiece on Jupiter.
Examining the stars of the Pleiades served upby the 17.3mm Delos, I was immediately struckby the pinpoint star images right to the edge ofthe field-of-view. Contrast was superb. Nor could
I detect any signs of off-axis distortions. On aAt a glance: TeleVue Delos eyepieces
Focal length
6mm
10mm
17.3mmApparent field-of-view
72 degrees
72 degrees
72 degrees

Available from: The Widescreen Centre
Details: www.widescreen-centre.co.uk

Eye relief
20mm
20mm
20mm

Weight
450g
408g
400g

Fitting1.25 inch
1.25 inch
1.25 inch

Price
£295
£295
£355

IN THE SHOPS

much needed eye relief
Q The Deloseyepieces are on theheavy side at over
400 grams. Image:Neil English.

dark, moonless night with my 152mm (six-inch)
refractor, I sat back and enjoyed the swirls ofnebulosity (reflection nebulae) around Merope.
The same was true with the 10mm Delos. Overall,I’d rate their deep sky performance as excellent.
With the first quarter Moon present in the sky, I
tested all three oculars for off-axis glare, comparing
them to a few mediocre eyepieces in my collection
known to exhibit light leakage. Placing the Moon justoutside the field-of-view, I can report that the Delosoculars suppressed moonlit glare exceptionally well,with stars at the other side of the field presenting asthey should against a velvet black sky.
One of the enduring questions raised by thesenew, super-comfortable eyepieces is whether they
can be considered to be worthy replacements oftried and trusted designs such as the venerable
orthoscopic eyepiece, especially in their ability topick off fine planetary detail. Over several nights, I
conducted careful comparisons of my 6mm Baader
genuine orthoscopic and the 6mm Delos. Both ocularsdelivered excellent images, rich in contrast and fully
the equal in terms of perceived light scatter. Indeed,
there was really little to choose between them, save forthe large difference in size of the field-of-view! Would
it be right to say that the restrictive field-of-view (42degrees) of the orthoscopic was a disadvantage in thisregard? In my opinion, no. There are some observers,

X Little and large:
how does theDelos stack up as aplanetary eyepiece?
Image: Neil English.

yours truly included, that find larger fields-of-view anunnecessary distraction when scrutinising a planetary
image or the aspects of a close binary star. You could
still say that a smaller field frames the image better.
I encountered only one major niggle while
comparing the Delos eyepieces with my other oculars.
Because the former are quite heavy compared tothe small but excellent eyepieces in my collection, I
found it an exercise in frustration having to adjust thebalance of the optical tube while switching between
lighter and heavier eyepieces. Those who are won overby the Delos eyepieces will be encouraged to collectthe entire range.
Neil English’s new book, Classic Telescopes, is now
available from Springer.

W The large,
comfortable eyelens of the Delos
eyepiece. Image:
Neil English.

“I WAS IMMEDIATELY STRUCK BY THE PINPOINT
STAR IMAGES RIGHT TO THE EDGE OF THE
FELD-OF-VIEW”
April 2013 | Astronomy Now | 77

IN THE SHOPSTeleVue ethos:
How wide can eyepieces go? Steve Ringwood tackles TeleVue’s Ethos rangeof eyepieces, with apparent fields-of-view up to 110 degrees.

Eyepieces have come far
since Galileo struggled withapparent fields of threedegrees that even at just 20× showed
him barely a third of the Moon. It
was Al Nagler who, in 1979, patented
the first truly wide-field astronomical
eyepiece, of 82 degrees. The samestable now has an Ethos range
boasting 100–110 degrees. Three ofthese long anticipated eyepieces have
now fallen into my hands (21mm,10mm and the SX 4.7mm) and I had
ready two telescopes just waiting togive them a run.
Early 2013 has seen Jupiterdominating the sky. Just as soon as
my f/10 305mm (12-inch) LX200 wasQThe 10mm Ethos
eyepiece on a305mm aperture
LX200. Image: Steve
Ringwood.

ready I moved to it with the 10mm
eyepiece. The four Galilean moons
were generously strung out either sideof the planet. Yet, at a magnificationof 305×, the leap from Io on Jupiter’seast to opposing Callisto in the west
straddled only half the field. To havea real field a third of a degree acrossembedded with a richly detailed jovian
disk was remarkable and an indicationof the treats to come.
Moving to the 110 degree
4.7mm eyepiece expanded Jupiter’s
disc to 648×, pushing at the limitsof permitted magnification, but
fortunately the night was a superior
one and Jupiter presented a richhorizontal tapestry of browns andmustard yellow. Remarkably, within

this smaller but still significant ten arcminute field, Io andEuropa were still in attendance! This counterintuitive
combination of high magnification and large scale isbreathtaking and reveals hackneyed objects in a completely
new light. However, wide-field eyepieces are not only about
more in one go.
A telescope’s fixed aperture delivers a finite amount oflight. Eyepiece magnification stretches this delimited light,
weakening its intensity. Although increasing magnification
dims the target’s luminosity, it has the same darkening effecton background sky glow. Ergo, increasing magnification
beneficially makes the sky field darker. It unfortunately also
makes the sky smaller because the greater power reduces
the real field of view – but not so with these cavernouseyepieces. At relatively higher magnifications you still viewa large patch of sky, with the bonus of a darker background(and hence better contrast).
With the Moon’s milky cast out of the way, I wasinterested in how well these eyepieces could do thisother job. Still armed with the 4.7mm’s true field of ten
arcminutes, I did not even trouble to switch to a lower
power as I glided south to the Great Nebula in Orion(M42). Simply astonishing. Through my vast 110 degree
window, buried in its cool glow, the nebula’s central
Trapezium stars were like icy coals in the hearth of a ghostly
fire. Contrast was incredible.

Edge of field
I hatched a plan to test how well these wide fields werethinning background light. Cautious to avoid too much
subjective comparison I had the brainwave of seating two
different eyepieces at once into my bino-viewer. With myready made ‘blink comparator’ the 100 degree 10mm Ethos
was clearly darker and richer than my equivalent 82- and68-degree rivals. This improvement of contrast was evenevident when I pitched the telescope back to decidedly‘non-deep sky’ Jupiter.
The Orion Nebula was truly spellbinding in the 21mm.
Be mindful that still at a relatively moderate magnificationof 145× I was drinking in a huge field of 41 arcminutes(much larger than a lunar diameter!). It was a stunning sightand beautifully held right to the edge of the field - indeed
all three of these highly corrected eyepieces held peripheral
field aberrations at bay with extreme unction. This huge
lower power field sent me chasing for the Andromeda“ONCE THE MOON WAS OUT
OF THE WAY, THE ENORMOUS
FIELDS PROVIDED BY THEETHOS GAVE SPECTACULARPANORAMAS OF EVERY CLUSTERAND GASEOUS SMUDGE I COULD
LAY MY EYES ON”
78 | Astronomy Now | April 2013

IN THE SHOPS

a wider view
Galaxy high in the west. How
wonderful to see, at 145×, not only theouter parts of the central condensation
but its M32 and M110 satellites too.
Still with the 21mm eyepiece,
I turned my gaze upon the Double
Cluster in Perseus. Even the field of
this eyepiece could not simultaneously
capture this binary cluster. Yet it
perfectly enclosed the clusters singly,
revealing them as incredible sights intheir own right. The scatter of stars
also usefully confirmed the eyepiece’s
coherence across the field.
I found the Ethos demands anarrow plane of observation. Placethe eye too distant from the eye lensand the full extent of the apparent
field is constricted. Yet eagerly lean in
too far, the iris is insufficiently large(particularly for older observers) toabsorb all of the exit pupil and you
get nulled visual areas called ‘kidneybeaning’ (common to all wide-fieldeyepieces). The rubber eye-guards
assist well in disciplining best position,although spectacle wearers may haveto get their glasses hard up against
these eye-guards. This, perhaps,is where the more generous eye
clearance of the Delos eyepieces comein. Yet, get the position just right andnot only do you enjoy the gargantuan
views but the eyepiece’s field stop
disappears behind your ears! All you
see is sky.

Enormous fields
Over the next few days a waxing firstquarter Moon made its appearance
in the evening sky and I beganobservation with the 21mm (145×).
The 41 arcminute field enfolded theMoon with alacrity, encircling it witha generous dark surround. What madethese observations unusual was thatin order to view different features atthis moderate power I had no needto gently slew the telescope towards
them; I merely viewed at will, my eye
alone alighting on what it wished. Likean Olympian god, incredible detail wasrevealed wherever I gazed.
With the mighty Apennine
mountain chain scything into theterminator, the glowering pit ofCopernicus was emerging into its

X The three Ethos eyepieces under review:the 4.7mm (SX), the 10mm and the 21mm.
Image: Steve Ringwood.

W Comparing field illumination between the100 degree 10mm Ethos and an equivalent82-degree rival. Image: Steve Ringwood.

morning glare. Its snow white circular cliffs blanchedagainst the inky crater floor. The higher power focal lengths
filled my visual field with crisply detailed lunar terrain.
Unconscious of the eyepiece field stops, the impression of alunar orbital EVA was tangible.
The 305mm f/10 having given its verdict, I pressed an
f/4.3 255mm (10-inch) Newtonian into service. Its shorter
focal length delivered much lower powers and wider fields.
The Moon at 51× was practically lost in the 21mm’s twodegree field. Yet once our deep sky spoiler was out of the way,the enormous fields provided by the Ethos gave spectacularpanoramas of every cluster and gaseous smudge I could laymy eyes on. One thing their wide fields did reveal is theneed of this shorter focal length light-bucket for a goodcoma-corrector. Yet even without one,the view afforded me of the Pleiades
captured in a single field is one that I
will remember for a long time.
These eyepieces provide incredible
vistas at remarkable magnifications.
Although these weighty eyepieces
may not suit some smaller telescopes,
I used the one kilogram (36oz)
21mm eyepiece to great effect on myCoronado PST!
Steve Ringwood is Astronomy Now’s
Equipment Consultant.

At a glance: TeleVue Ethos eyepieces
Focal length
4.7mm (SX)
10mm
21mm

Apparent field-of-view
110 degrees
100 degrees
100 degrees

Eye relief
15mm
15mm
15mm

WeightFitting590g
2/1.25-inch
499g
2/1.25-inch
1.02kg Two-inch onlyPrice
£525
£525
£720

Available from: The Widescreen Centre
Details: www.widescreen-centre.co.uk

April 2013 | Astronomy Now | 79

IN THE SHOPSTeleVue eyepieces:

The verdict

Our two reviewers, Steve Ringwood and Neil English, put their heads together to determine
which range or combination of Ethos and Delos eyepieces provides the best views.

B

oth the Ethos and Delos eyepieces deliverwide fields with very high physical and opticalspecifications. The Ethos, with its huge, highly
corrected apparent field of 100–110 degrees has beensuch a great hit with the astronomical communitythat the Delos was born to afford a similar standardof performance that was kinder to spectacle wearers.
In order to extend the Delos’ eye relief to a generous
20mm, the apparent field was narrowed to a still boastful
72 degrees.
The optical gymnastics required to achieve theperformance of these remarkable eyepieces requires
quite a number of glass elements and this inevitably
makes both designs quite weighty. Furthermore, unlessas mentioned in the Delos review you can fund a wholeset, continually rebalancing a small instrument might
become onerous. Yet that other concern of multi-element
eyepieces, internal reflection (ghosting) and absorption
were not found in either review, countered throughthoughtful design and superior coatings.
The Ethos eyepiece is remarkable in that the visible
field stop is practically out of the range of peripheral

W TeleVue produce a huge variety of eyepieces – but the Ethos
and Delos really stand out from the crowd. Image: Max Alexander/
Astronomy Now.

V The wide field-of-view of the Ethos eyepieces can be addictive. Image: Steve Ringwood.

vision – permitting the conceit that
there is nothing (not even yourtelescope) between you and theuniverse. The Delos is probably tobe preferred by spectacle wearers andperhaps less experienced observers
who might find its generous eye
relief friendlier to use.
These eyepieces will work wellon most types of telescopes, but
do bear in mind that in order forthem to work well with rich field
instruments, a good corrector, suchas the Paracorr type 2, will allow
them to produce best results. For
instruments with slower f-ratios,
both the Ethos and Delos range
work flawlessly.

Mix and match eyepieces
Of the three Delos eyepieces
reviewed here, the reviewer (Neil)found himself using the 6mm model
most often (as a planetary anddouble star eyepiece) followed by
the 17.3mm. Since the launch of

the original trio of Delos eyepieces,
TeleVue have introduced a handfulof new focal lengths in the range –3.5mm, 4.5mm, 8mm, 12mm and14mm.
Which of these eyepiece ranges– Delos or Ethos – best suits you?
That depends on your budget, as
well as your preference of a 72
degree field-of-view over a 100-plus
degree field-of-view, or vice versa.
The Delos eyepieces, which areworthy successors to the venerable
Radian eyepieces, are considerably
less expensive than the Ethos range.
And while some observers will findthe 100 degree experience quite
addictive, others will conclude thata smaller, 72-degree field will suit
their needs better. Or perhaps, yourneeds are best met by a judicious
selection of both? Whatever yourchoice, you can be assured of top
quality, immersive views of the nightsky. Something we all have come to
expect from TeleVue.

“THE DELOS EYEPIECES ARE WORTHY
SUCCESSORS TO THE VENERABLE RADIANEYEPIECES AND ARE CONSIDERABLY LESSEXPENSIVE THAN THE ETHOS RANGE”
80 | Astronomy Now | April 2013

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