[ngcles]

Hi All,

Yep, it was the Nov/Dec 2003 issue of Sky & Space where I did the review on the GSO dob. I've got a copy of it lying around somewhere -- probably filed out in the shed somewhere inaccessible so I'll go from memory as I really don't know how long it would take me to find it.

I'll say this up front -- I'm not going to cast a definitive vote for one over the other. That would be decidedly unfair on both telescopes as they were nearly 5 years apart and I’m going on memory for one of them. I haven't carefully examined a GSO for a while and things might well have changed from the one I looked at — which was a good ‘scope as I said. There is no way that I could do a comparison/evaluation and make a value judgement on that basis. What I’ve written below is a few notes on (my memory) of the two reviews 5 years apart and should be strictly viewed in that context. More importantly it would be unfair on both magazines to cast a vote either way. Again, please bear in mind I'm going on memory — the GSO test was five years ago.

The Skywatcher is a few hunderd dollars more expensive than the GSO. The exact extent of the difference depends on where and when you shop, so shop around for the best deal on either unit.

The execution of both 'scopes in many cases is basically pretty similar. The GSO I tested back then had (I think) a rack and peanut focuser which works fine but a crayford is definitely better. GSO now offer that and it comes with reduction gearing for micro-focuser. having said that, the standard focuser (no microfocuser) on the skywatcher I tested was very good and pleasant to use, but did have a wobbly set-screw -- which I wouldn't expect on every one. I assume it was in all likelihood a simple one-off manufacturing fault.

The paintwork/finish of the tube on the skywatcher was certainly of a high standard and one thing I didn't include (couldn't fit in the space) in the article was the "seamless" tube — the tube has no folded seam like other Newtonian tubes but is instead welded — and I couldn’t pick the weld. Very nice workmanship. The matte black on the inside of the skywatcher was definitely a better finish. But, if I owned either, I'd be installing German black cotton velvet anyway.

Leaving aside colours, the dob base/mount on both is basically similar. The edges/trim of the skywatcher just looked/felt a bit tighter and the GSO I looked at 5 years ago just not quite as well sealed at the joints. Of course that can be fixed with a bit of silicone goo. As I remember, the execution of the altitude bearing is a bit different -- the GSO is a more traditional approach. Neither are bad at all. The Skywatcher's base has to be a bit wider/bigger to accommodate the trunnions inside the side-tines of the mount. The skywatcher’s design also provides, in effect, a clutch on the altitude bearing that is different to the GSO spring system.

The lazy-susan flat bearing making the azimuth bearing in both cases is functionally, if not essentially identical. In the case of the Skywatcher it is sandwiched between thin metal plates. In the GSO one I tested (again, 5 years ago) that didn't have the plates or similar. The bearing had been packed immobile and apparently under a little pressure (for who knows how long) between the groundboard and the bottom of the rocker. As a consequence, the rollers had left little dents in the formica on the bottom of the rocker so that when it was rotated in azimuth, it sounded (and felt a little) like a train going over the joins in the track -- gadunk, gadunk, gadunk, gadunk, gadunk, gadunk, ... etc. I can’t remember whether I mentioned that in the review and again, this was apparently a one-off fault or at least very uncommon. It could easily be cured in any event by sandwiching the lazy-susan bearing between a couple of old-fashioned LP records you can buy at any op-shop for 50c each (and already have pre-drilled centre holes).

The mirror cells were again very similar in design except that the skywatcher is all metal and more robust. The collimation adjustments on the skywatcher were very fuss-free and no tool. There were quite a few plastic components on the GSO in the cells. Both were 9 point cells. The spider vanes on the GSO I looked at were somewhat thicker (though not too bad) and would produce more diffraction effects over the skywatcher. Has this changed? Dunno. Is there still plastic in the GSO cells? Dunno.

Some GSO's have pyrex mirrors while others are float-glass (plate glass) substrate — you get the choice depending on the model. Pyrex is a decidedly better material because of the very low coefficient of expansion, but float-glass is cheaper. The pyrex mirror will hold a better figure in all temperatures. The Skywatchers are all pyrex mirrors.

I’m pretty sure the GSO I tested was a pyrex mirror. The optics were very good and lost little to my own 12”. I was very, very impressed by the smoothness and figure on the Skywatcher’s optics, though for purely visual use, it could easily accommodate a smaller secondary but still have a good-sized 100% illuminated field.

Bottom line is the Skywatcher is a very good ‘scope out of the box as I said in the review. Does this justify the price difference? That’s up to you. Is it good value for $1300 (again, shop around they can be got cheaper)? I reckon so.

Put in context, back in 1998, I made (assembled) a 12” Newtonian tube assembly for my Samson GEM. The mirror is a 50mm thick 307mm diameter f/5.3 pyrex Deep Sky Optics mirror by Mark Suchting (Satchmo). It is an essentially flawless mirror. In its aperture class I’ve not seen one better — period. Mark actually made it for a project for himself and then changed his mind and sold it to me. So, it is not only a Suchting mirror, it was one made for the maker himself— I think you get the picture. The tube is a 70/30 split tube of 1mm thick sheet aluminium which is fully baffled (9 baffles) and is cleverly reinforced. It was engineered by Gary Mitchell. The tube is so solid, you can sit on it (I weigh 100kg) without deformation. The cells are Novak, the focuser is a JMI NGF-2. Despite all that it weighs in at just 19kg! Frankly, it is as good as a visual-use 12” Newtonian can get, simple as that. With a larger secondary it would be a brilliant astrograph too. But, in 1998 that tube assembly alone cost me a total of nearly $2,600- to assemble myself.

How much are the skywatcher (or indeed GSOs) by comparison for a complete telescope with eyepieces?

Thanks very much for the comments on the S&T test report -- much appreciated. Glad it was of value to someone.


Best,

Les D