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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.