Vixen A70LF Review
I bought this, ready mounted on Vixen’s Porta, for a certain small
child. It’s worth a review, because it is a prime example of the kind of scope
that many (adults and children) will encounter as their first, if they’re
lucky.
Why lucky? There are of course numerous such refractors available from
toy stores, department store, camera stores and Ebay, after all. When I say ‘lucky’
it’s because most of those Ebay and store scopes are just rubbish. Reviewers
like me shout ourselves hoarse at Christmas trying to persuade parents not to
put one under the tree. But such ‘department store scopes’ tend to be marketing
exercises with poor optics and crummy accessories.
Now given that Vixen has an old and illustrious name in amateur
astronomy, I hoped that the A70LF would be much better than your average toy
store refractor. Let’s see if it is …
At
A Glance
|
Telescope |
Vixen A70LF/Porta |
|
Aperture |
70mm |
|
Focal Length |
900mm |
|
Focal Ratio |
F12.9 |
|
Length |
860mm |
|
Weight |
1.9Kg |
Data from Vixen.
Design and Build
The A70LF is typical of Vixen’s bottom-range scopes and is
probably a re-badged Synta from China, a close-relative of a basic SkyWatcher, but
none the worse for that.
Optics
Optically, the A70LF is a simple longish focal length (900mm, F
12.9) air-spaced (with the usual foil spacers) achromat from Vixen’s current
(white and black) range of refractors.
A good long focus achromat (as opposed to a useless toy store
device with plastic lenses) has some key advantages for visual use:
·
Much lower chromatic aberration
(false colour). An F12 design like this one should be virtually CA-free for
visual use – APO not required!
·
Long focal lengths are less
collimation sensitive.
·
Long-f lenses are easy to make
well due to the less pronounced curves.
·
High magnifications for the Moon
and planets don’t require expensive specialist eyepieces, simple plossls or
orthos will do fine.
Foil-spaced
achromatic objective lens.
Tube & Focuser
Though long at 34”/860mm, the OTA is very light weight (1.9kg) –
great for kids or as a budget guide-scope which won’t strain a small mount. To
this end, the 1.25” focuser has a lightweight, but high-quality, plastic body
with a metal draw tube. Focusing is well-weighted and precise, however – better
than the Synta all-metal 1.25” unit found on the ST80.
Overall fit and finish is good and the OTA interior well baffled
and matte-painted. Light weight but good quality cast rings are provided with a
Vixen dovetail.
Mounting
The A70LF was supplied as a package with Vixen’s excellent Porta
mount. The Porta has a standard dovetail interface and features push-pull and
slow-motion control. It’s well-made, robust and stable, as well as being fairly
light.
The Porta has some clever features, like a set of Allen keys
hidden beneath a rubber mat (handy for the odd accessory or your glasses) on
top for easy tension adjustment of the push-pull action. Its small round
eyepiece tray can stay on when you kick the legs in to fold them for a quick
grab-n-go.
The A70LF
mates to the Porta with a standard Vixen dovetail.
Vixen’s Porta
mount is top notch – easy to use and stable. The legs handily fold in for a
quick move outside.
Vixen’s
‘silver-top’ Plossls have become minor classics.
Accessories
The accessories are a mixed bag. The eyepieces – 20mm and 6.3mm
giving 45x and an optimistic 142x respectively - are silver-top Plossls, are
very good indeed and would stand a scope-upgrade later on. The diagonal is a
good-quality prism type.
However, the finder is a toy-scope item: plastic singlet lenses
with the most horrible, dimmest view imaginable and a plastic finder-mount
which won’t hold alignment. Unfortunately, the fitting is non-standard so there
is no easy way to fit an RDF. This is the A70LF’s big drawback.
In
Use – Daytime
The A70’s
optics are perfectly up to some daytime spotting or casual birding, but it’s
much too bulky for anything more serious.
In
Use – Astrophotography
With a 1.25”
only focuser and a long F-ratio, the A70LF would take great snaps of the Moon,
but probably not much else.
A quick DSLR snap of the Moon taken with a long-f
achromat of similar aperture to the A70LF.
In
Use – The Night Sky
It annoys me when manufacturers sell short-tube refractors with
optical finders – the thing is a
finder! However, the same comment doesn’t apply to a 900mm focal length like
the A70LF. The reason is that a longer focal length gives a smaller field of
view. That means the A70LF delivers a maximum (with a 32mm Plossl) field of
just 1.7 degrees. Compare that to a 55mm plossl in an ST102 giving a whopping 5.3
degrees.
However, in practice the A70LF is even worse, because the 20mm Plossl
supplied yields just 1.1 degrees. With a field that narrow you really need a decent finder, but effectively
the A70’s is so useless it effectively has no finder at all.
What all that means is big frustration for a child. They just
can’t find stuff. Even the Moon is a struggle.
Once you find things, though (which means Dad helping out) the
view is very good indeed.
The
Moon
As expected, there is no chromatic aberration worth mentioning and
the Moon looks fantastic. That 6.3mm plossl seems like a crazy power for a beginner’s
scope, but the A70 takes it and delivers wonderful Lunar views.
The Planets
The planets look good too, with the quality optics ensuring you
get to see Jupiter’s cloud belts, Saturn’s rings and Venus’ phases.
Deep
Sky
The small aperture and long f-ratio aren’t ideal for deep sky, but
again the A70 works surprisingly well. Bright DSOs, like the Orion nebula and
open clusters like the Double and the Pleiades look great with sparkly
pin-sharp stars.
Make no mistake, on many targets the A70LF delivers performance on
a par with a TeleVue Pronto, also a 70mm achromat.
The Sun
There is one purpose for which the A70 is particularly well
suited: solar projection. The long focal length and modest aperture work well
for this application (and the end-cap has a little aperture stopped with a
plastic cap for the purpose). What’s more, at this price there’s little worry
about getting it wrong and burning some part of the OTA innards! I’ve had many
good views of sun-spots (projected onto a sheet of paper) with the A70 and it’s
one of the best and cheapest ways I know of getting into solar viewing.
Please Note: (!!! Never, EVER look at the Sun through the
eyepiece!!!).
Summary
The A70LF I had performed surprisingly well and had excellent
optics and decent mechanicals. The Porta mount is excellent.
Unfortunately, the finder problem spoils the party as a child’s
scope: The A70LF is not suitable for children for this reason. I ended
up selling it because my daughter couldn’t learn to find things without a
finder and we couldn’t easily fit an RDF.
The basic concept of small aperture and long focal length
certainly works though, delivering Solar System views close to that of a much
more expensive 3” semi-APO.
The little Vixen makes an interesting comparison is to another long
focal length refractor: my 1960s
Unitron. Mechanically the Unitron is better of course (it was, relatively
speaking, a much more expensive telescope when new), but optically the Vixen is
far better. The A70 is also much better than that ‘70s Tasco I mentioned in the
introduction. So in some ways it’s reassuring to see that cheap telescopes have
improved! Talking of cheap, a friend picked one of these up brand new for £25
on Ebay, which must be the bargain of the century for a lightweight guide
scope.
Recommended as a grab-and-go, guider or a knock-about solar scope,
but not for children due to the small FOV combined with useless finder.
