Skywatcher 120mm Achromatic Refractor
Submitted: Tuesday, 21st February 2006 by Mick Stevens
Skywatcher 120mm (4.7") Acromatic Refractor - FL 1000mm, f/8.3
A few years ago I purchased a Skywatcher 120mm f 8.3 achromatic refractor on an EQ5 mount after using it for some time I decided it might be constructive to share my experiences with this 'scope.
There are probably more than a few ameatuer astronomers who are confronted with the skywatcher who may automatically dismiss it as a bargain basement, cheap'n' nasty piece of junk from China. This is an incorrect but quite a natural reaction. There are so many exceptional quality apochromatic refractors on the market that it is easy to assume that the inexpensive achromat is as Bill and Ted might say " not worthy". The truth is the 120mm Skywatcher represents excellent value for money, for well under $1500 you get a telescope that only 10 years ago would have cost a premium.
Go Low Go Wide
Well enough of the waffle, what about the optics? Chromatic aberration (CA) is probably the main concern with achromatic refractors and yes the skywatcher does suffer from this ailment BUT not to a great degree. Planets like Venus, Jupiter and Saturn do present a purple halo which some do find distracting but which I barely notice. 2nd magnitude or brighter stars also show a trace of CA. but in deep sky scenes CA is totally absent. Planetary and Luna views through the skywatcher show a lot of detail and the Telescope is ideal for double stars. I have split the companion to Antares on a average night and viewing Rigel's companion is routine except on the worst of nights. Star images either side of focus are identical except for a slight colour shift verifying the existance of CA.
Punching Above Its Weight
When I was a kid starting out in astronomy many of my books were written by Patrick Moore. When reccomending a beginners telescope he would always recommend a 3" (75mm) refractor or 6" (150mm) newtonian reflector. I always thought that was a bit harsh on the poor reflector but it does illustrate the superior light gathering abilities of a refractor. The skywatcher is no exception.
The skywatcher appears to have a fully multicoated objective lens which does wonders for the contrast. Coupled with the fact there is no central obstruction the Skywatcher is going to be a winner on an object with low contrast, Nebulae, planetry detail etc. The effect on nebulae is by my reckoning the same as viewing the same object with a 150-180mm Newtonian. While testing for this review I observed NGC 2359 (thors helmet) a nebula in Canis Major. Under the light pollution of Perth I didn't expect to see it at all but swept it up fairly easily as a faint indefinite haze, the view improved with averted vision. The view improved big time with the addition of my trusty OIII filter, the nebula was conspicious and very beautiful showing its familiar bust shape (standing on it's head).
Is It a Winner?
The Skywatcher seems to be well built and the finish is good. The tripod an EQ5 with rolled aluminium legs is barely adequate and would benifit much from a tripod upgrade. I have seen 120mm skywatchers with stainless steel tripod legs which would be a better option. There is not too much plastic on the set up except for a few knobs and some odd's and ends. I replaced the focusing knobs with oversized aluminium ones. I also plan to get a drive for the scope so I can do more double star viewing in the future.
Would I recommend this telescope, Yes. For the price it is truly a bargain and despite a few flaws I outlined above it is a very versitile instrument for general astronomy.