Tele
Vue Genesis (Non-SDF) Review
Fast, flat-field astrographs using the
Petzval design have become common in recent years – think Takahashi FSQs,
Vixen VSD and Tele Vue’s own NP-101 and NP-127 and Chinese copies
marketed by various brands. But the Petzval is just an old-fashioned
four-element camera lens design that Al Nagler of Tele Vue adopted for
telescopes in the mid Eighties. One of those early Petzval designs was the
Genesis.
The Genesis on test here was owned by a
friend and taken by me in a part trade for a Takahashi FS-128. I didn’t
know what to expect, but found a very interesting old ‘scope, as we will
see.
Note that this review covers the
non-SDF Genesis models. The SDF is a rather different beast, produced before
the NP101.
At
A Glance
|
Telescope |
Tele Vue Genesis |
|
Aperture |
100mm |
|
Focal Length |
500mm |
|
Focal Ratio |
F5 |
|
Length |
About 650mm |
|
Weight |
About 5 Kg |
Data from Me.
What’s
in the Box?
Like most Tele Vue 4” refractors,
the Genesis comes in a nice hard case.
Design
and Build
The Genesis is deceptively similar to
much more recent Tele Vues and shares most of their build characteristics. The overall appearance of this
Genesis is subtly different from the later SDF version and it’s smaller
too.
Optics
I have written about Petzvals at
length in the NP101 review. The Genesis is a similar quadruplet design with an
ordinary doublet up front and a second doublet reducer-flattener just in front
of the focuser to make four elements in total. It’s a design now shared
with other flat-field refractors, such as Takahashi’s FSQ models.
The front doublet is held in a slim and simple cell attached
to the tube by rivets or blind-headed screws. The collimation is set at the
factory by carefully nudging it into place on an optical bench and then fixing
it (no adjustment is possible) – sounds crude but works out fine.
Multi-coatings are good, but not quite up to modern standards.
The rear Petzval lens allows greater freedom to correct
monochromatic aberrations, like field curvature and coma, than most other
designs, but it doesn’t correct chromatic aberration. Instead, the
‘trick’ is that it reduces the focal length by about half (down to
a very fast 500mm, F5 in this Genesis). That means the front doublet is
actually about F10.
On these early Genesis models, the front doublet is an
achromat, but one with a large air gap to improve correction. That and the
focal length of F10 substantially reduces false colour, but doesn’t
eliminate it.
The Genesis is labelled ‘fluorite’, but here that
is a little disingenuous. In a Takahashi, a fluorite element allows the doublet
objective to be apochromatic. In the Genesis the magic mineral is in the
Petzval element and has little or no effect on false colour according to optics
guru Roland Christen.
The later F5.4 SDF model needs a mention. The
‘SD’ indicates that the doublet at the front has a fluoro-crown element of Special Dispersion glass of some
sort, making it an apochromat. Consequently, false colour correction is much
better than these early Genesis models. However, ‘SD’ as opposed to
‘ED’ in the NP101 likely indicates an older type of fluoro-crown glass and so the SDF reputedly doesn’t
have quite the later NP101’s perfect correction.
The punch line to all this is
tech-talk that the early Genesis reviewed here is an achromat, albeit one with
a fast, flat field and the reduced false colour of a slower achromat.
Petzval lens of the near-identical (only brass) Renaissance
model.
Painted dew shield and anodised lens cell.
Tube
Whereas the later (f5.4) Genesis models (like the NP-101 that
replaced them) were finished in cream pebble-finish powder coat with a black
anodised dew shield, these early models have a traditional gloss white tube and
dew shield, though the latter slides over a black anodised lens cell. Otherwise
the Genesis is similar to later Tele Vues – a short, slim OTA, simple,
but all beautifully made for the long term, so very different from most
mass-produced telescopes today.
The F5.4 SDF model seems to have been longer than either the
early Genesis reviewed here and the later NP101.
Like most Tele Vues, the Genesis benefits from a screw-fit
metal lens cap (‘screech, screech,’ as it’s unscrewed,
‘CLANG,’ as you fumble and drop it with freezing fingers).
Again, like other Tele Vues the tube has no baffles, it is
just lined with what looks like (and may actually be) black painted sandpaper.
Focuser
The Genesis has the usual (for pre-imaging Tele Vues) heavy
cast focuser body and chrome draw tube running by rack and pinion, with a
2” visual back and single lock knob. Oh, and you get solid chromed
focuser knobs, like chromed versions of the brass knobs on a Renaissance,
instead of the trademark later Tele Vue “Mag’ wheels”. Like
all early Tele Vue focusers, it’s super smooth and easy.
Mounting
The Genesis
has the trademark Tele Vue clamshell mounting ring. It has ¼-20 threads
on the bottom so you can mount it on one of Tele Vue’s alt-az mounts (Panoramic or Gibraltar). Alternatively, you can
get a short dovetail to fit which is CG5/Vixen compatible, but has matching
¼-20 threads on the bottom and a machined in lip so you can put it
straight on a Tele Vue mount as well without removing the dovetail –
neat.
That’s
handy, because TV clamshells require some effort with an Allen key to open!
Accessories
It goes without saying that Tele Vue
make loads of accessories, like eyepieces and barlows.
The Genesis clamshell has a dovetail to fit a Tele Vue ‘Star Beam’
red-dot finder as shown in the photos.
The genesis comes in a hard case, not dissimilar to the one
for a modern Tele Vue, except that it’s brown.
In
Use – Daytime
Unlike many astro’ scope makers,
Tele Vue has always advocated using its telescopes during the day for spotting
and nature viewing. The Genesis gives a wonderful daytime view – pin
sharp, bright and flat. Use a widefield eyepiece – Nagler, Panoptic or
more recent Ethos or Delos – and you are treated to a real picture window
view. Only at higher powers and on high contrast subjects does a bit of false
colour creep in.
In
Use – Astrophotography
Off axis aberrations are well
controlled by the Petzval lens, though not to the same extent as an NP-101.
Still, stars remain nicely pin-point to the edges of an APS-C frame.
Back in the day, as the manual says, TV
intended the Genesis to be used as a telephoto lens for a 35mm camera, so
coverage on APS-C is pretty good, with just a little drop-off in the corners.
There is a problem though and it is
false colour. The Genesis’ achromatic nature shows up when imaging and
every white or blue star is surrounded by a pretty blue halo. Fine for casual
imaging, with a fast speed and flat field, the Genesis is not for the keen
imager.
Below are unprocessed single APS-C
frames of the Pleiades and the Moon taken through the Genesis. Note the false
colour which is visible on the Lunar limb too.
In
Use – The Night Sky
General
Observing Notes
The Genesis
may basically be an achromat, but otherwise optical quality is very high.
People worry about collimation with Petzvals, but
this one is certainly spot-on. Focus is snappy and the Genesis takes high
magnifications well.
Cool
Down
The doublet design of the Genesis means it cools quickly when
you put it outside and is ready to use after just a short cool-down period.
That makes it a handy quick-look scope.
Star
Test
The star test
looks excellent.
The
Moon
According to the theory the Genesis should display chromatic
aberration like a 4” F10 achromat. Now the rule about chromatic
aberration in achromats is that to display “acceptable” CA levels,
their focal length should be longer than about 1.22x their aperture in cm,
which in this case would be about F12. So you might expect that the Genesis
suffers from quite noticeable CA at higher powers; it does. At medium
magnifications, the Moon is sharp and contrasty, but above about 70x it is surrounded
by a pretty purple halo. At higher magnifications still, 100x and more, even
crater shadows are washed in purple, though everything is otherwise very sharp
and detailed. Repeat after me “it’s
an achromat”! But whilst
it’s not an NP101, the Genesis is not a Sky-Watcher StarTravel
102 either and it is quite usable for the Moon.
Jupiter
High power planetary viewing is a very colourful experience
with the Genesis, though in other ways the optics hold up under high powers.
Unfortunately, used as I am to APOs, I find a lot of CA rather hard to take and
seeing Jupiter embedded in Imperial Purple isn’t the way I like it.
Deep
Sky
I recall the time I first popped a Nagler into the Genesis
and looked at the Orion Nebula. Given the large number of times, before and
since, that I have looked at M42 that’s surprising. The view was just
amazing – so flat and wide with such pinpoint diamond stars right to the
field stop; at last that space walk they talk about.
I was hooked. The Genesis is a telescope for sweeping star fields, for brighter
DSOs and clusters. The Pleiades has never looked better and Andromeda is
particularly detailed with that wide field.
Consider that very few 4” refractors have focal lengths
of 500mm or less and even fewer combine it with a flat field. Takahashi’s
FSQ matches it and the only scopes with less are the rare Pentax SDUF F4 and
similar Vixen VSD100, but that is purely for imaging and very compromised for
visual use. So 25 years on, the Genesis is still a rare visual instrument
– supremely fast bright and wide. My guess is that sweeping for clusters
is Al Nagler’s favourite thing and that is certainly what the Genesis is
optimised for.
Summary
I loved the Genesis on deep sky, but the Genesis is less
ideal for the Moon and planets due to significant false colour. All Tele
Vue’s Petzvals give peerless deep sky views,
but unlike the NP-101 the Genesis is pretty much a specialist visual deep sky
scope. Someone recently said to me of the NP-101 (and I quote) “Oh
the sharpness. Open clusters are mind blowing through those things.”
Exactly the same could be said of the Genesis.
After perhaps a
quarter of a century of, I would say, very regular use, the Genesis still
performed flawlessly. The focuser was smooth and precise, the optics pin sharp
with collimation spot on. And it still looked great. Tele Vues are solidly
built. People talk about a “legacy telescope” and I suspect that
Genesis will still be delivering lovely views long after both Al Nagler and I
have gone. True, it’s not an APO and the NP-101 is vastly better in that
respect, but for low to medium power wide-field viewing the Genesis is
unequalled.
Confession time: on an
emotional-attachment level, I think I liked the Genesis even better than the NP-101,
for reasons that I find hard to explain. I preferred its looks and I think it
was slightly shorter; perhaps it was even flatter and more stunning on deep
sky. Its quirky single mindedness gave it character. Interestingly, the friend
I bought it from still regrets selling it and reckons it gave him his finest
views of extended DSOs like M31.
If you mainly like
sweeping star fields, then Tele Vue’s classic Genesis is highly
recommended, just remember it’s not an APO, so price accordingly.
Updated by Roger Vine
2018.
