Review of 12 inches Dobson "Scopic" by Astrotech

Fig.1 - The green laser beams at Jupiter, near the Moon (on March 28, 2004, 20:29 CET).

Let me first say that I have no undisclosed interest in reviewing this telescope and especially no economical return. Nevertheless, I had a role in triggering the development of this interesting scope, which is explained in the review. Thus I feel it partly like the embodiment of an idea of mine (but, I am not involved in any way in making or selling it). I am making my best efforts to be unbiased and thus I have cancelled any hyperbolic statement.

The scope reviewed here is a final pre-production prototype, which I have been able to use for some months -from January to June 2004- because the maker asked me to be a "beta tester" (thanks of my involvement in the initial idea).

Here is the story of how this scope was born. The producer, Giovanni Dal Lago, is an amateur astronomer who has a selling point here in Italy (Astrotech). In spring 2002 it happened that I bought a little apo and needed customer assistance (I wanted to compare the star test with another sample). We then met one night and, after the comparisons (BTW passed by the apo), we went into a nearby bar and began to talk about "the ideal scope". Soon I explained him that "the ideal visual scope" for me was a dobson, possibly like the Teleport or so (if possible bigger): a scope that folds in itself but should have a size of at least 12".... (possibly 16" for me). That discussion convinced him to produce an idea he already had since a long time: a telescope with a telescopic tube that he named "Scopic". The pictures show the final prototype. Before the onw reviewed here, there was another earlier prototype, whose mirror box was made of wood. The scope now is made of metal, mostly alluminium, and manufactured by a friend of him, also amateur astronomer: Giovanni Ariot, who is a mechanical engineeer and own a little mechanical workshop where he makes textile machines for his living (and now makes the Scopic too). Both prototypes were extensively tested by them two, and the latter, the one reviewed here, was then given to me for a second phase of testing (I am a mechanical engineer too), and I think to other people too. As expected I found a few remaining bugs and suggested some improvements that, as far as I know, are going to be included in the next production batches and which I will explain in the follwing.

Fig.2 shows the set up of the telescope which is breezing fast: one drops the ground board and rocker, place the telescope box on the teflon pads (the four white disks), remove the lid, extend the telescopic tube by pulling the upper segment and then put the focuser board on. That is all, and that takes about 30-40 seconds. This is definitely a "grab and go" scope, but it is a 12 inches grab and go!

The heaviest part of the scope is "the box", which is ~23 kg (~50 pounds), including the optional accessories described below. The box has two handles on top, which however I found to be a little bit too streamlined. I suggested to replace them with larger ones and to provide attachments for a shoulder strap. The weight is easy to carry for me: walking tenths of meters with the box resting on my stomach and even making short stairs was not difficult (for me). Nevertheless I understand that some people might prefer the box to be somewhat lighter: in that case a shoulder strap could be the most effective help in my opinion (but other helps could also be used, of course).

I think that 12" is the largest size for which this scope concept results easy to use. A16" would have a box a little bit too heavy for a one-man setup. Smaller sizes are feasible, of course, but 12" is definitely the largest useful size for the concept in my opinion; and that is why of that size.

The lid is kept in place by three smal magnets, and when removed, it can be attached to the box back, where there are three additional magnets (see picture 3 lower left).

The extension of the telescopic segments is achieved by simply pulling. There are 5 latches that lock each tube segment when full extension is reached. These mechanisms is where most work was done by Giovanni Ariot in the development between first and second prototype. Folding down the tubes is conversely achieved by turning the tubes clockwise, which frees the latches. Safety locks prevents unwanted rotation and must be released before turning the tubes counterclockwise. A detail of one latch is seen in Fig.3 (upper right below the switch of the fans).

Mirror and optical performance.

First, one should note that the telescope review is primarily about the structure, which may be fitted with ample choices of mirrors. That said, the prototype I used was sporting a 12" mirror made by Orion Optics UK. According to the manufacturer's websiste, their mirrors are produced in three classes of quality: standard (better than 1/4 wavefront PTV), premium (better than 1/6), research (better than 1/8). It seems to me that the classes result from a selection process: the mirrors come out of the same line and are divided, after interferometer testing, into the three figure groups. A Zygo interferometer is used for the purpose (the research grade is sold with its interferometer report). All that should mean that each class does not exceed the quality of the next. The mirror of this scope was a "standard" one, which means it should have been between 1/4 and 1/6 wavefront PTV.

There are two options for coating (standard and high reflectance, called Hilux) and two for the substrate (pyrex or zerodur). The mirror in this scope was pyrex and standard coating.

In other words the mirror I got was the least expensive: standard class with the standard coating in pyrex. It was choosen that way because Giovanni was interested at evaluating the performance of a "entry level" version (to be made, of course, without fans and laser too).

So, how does the above mirror behave? I have tested it for many months, from January to June, on planets and other targets, often side by side with my 16" dobsonian.

The star test reveals clear signs of incomplete correction of the spherical aberration. Inside focus the diffraction rings were contrasty and well marked, but outside they were softer. At the beginning I thought the mirror to have a sort of turned up edge, but I soon realised it was the residual SA. Although the star test clearly revealed the above imperfections, I think however the amount of residual SA is whithin the declared quality (between 1/4 and 1/6 wavefront PTV). In fact the performance, in terms of roll-off magnification, is in agreement with a mirror of that quality: on Saturn and the Moon I was often able to obtain crisp images at about 430x and above, which means 35x per inch or better. On Jupiter the most frequent magnification with crisp views was 323x, or 27x per inch (according to Mel Bartel's rating criteria it is a "good" mirror). Compared to my 16" the mirror was only a little short in terms of resolution but only after the big 16" was perfectly cooled, which never happened before than a couple of hours. In the first two hours, the lighter and thinner 12", always bested the big gun. Active boundary layer cooling was a great help here, making the scope to reach top resolution in a matter of minutes; but even without using the cooling fans, the thinner 12" mirror was much faster to cool down and sooner producing crisp images (perhaps thanks also to better heat conduction/radiation of the metal box). On Jupiter the details were much better that those shown by a typical 8" SC. Tiny coloured festoons, white spots, and the like were much much better seen than in my previous (and good) 8" Meade Lx 90.

Indeed I think this scope may a valid alternative to either a 16" dobson and a 8"-10" classical SC. Compared to the 16" the advantage is in set up time, and portability. the cons is a slightly less power. Compared to a 8"-10" SC the advantage is much more power, and portability.