On the large diameters there is no competition (from a mechanical point of view, I did not test the optics)! At least if one compares the actual 18" SW and the ES 20" prototype. Actually (if the optics are as good as the mechanics) the 18" SW can compete with high-end Dobsons, as Apollo pointed out.
The 18" SW is solid as rock, without being heavy, and smooth in the movements. It will be commercialized in France starting next week (the vendor Optique Unterlinden received already 5 scopes)
The 16" ES is already distributed in France. It looks to me a little too light already for a 16".
The ES 20" is just a prototype. The prototype is a just a scale-up of the 16" model. This is not good to me. Testing the movements and the stability of the 20"-ES-prototype at the Paris-expo I got the impression that the structure is too light to keep collimation for these diameters and the movements were not smooth at all. They have to rethink the 20" from scratch as SW did if they want to go beyond a 16".
On the contrary the SW is so robust that it could easily be scaled up to 20-24" or to shorter focal ratio than f/4. I hope that they will take this way.
If they come out with a 20" with a f3.6 or even better a f/3.3 with good optics, I will buy it immediately!
Notice that the 6 truss-bars of the 18" SW can be spitted in two, to reduce the bar-lenghts for transportation.
If I have to suggest a simple mechanical improvement to SW, I would add the possibility to attach (just during transportation) two wheels at the end of the altitude bearings (on the back-side) to easily transport the mounted-tube (see the schematic wheels location in red in the attached figure). Given the solidity and rigidity of the structure, this modification would allow a single person to move quickly the Dobson without the need of mounting and unmounting the tube-structure. If I buy it, I will solder two attachments for the wheels, to move the Dobson mounted from the house to the garden.
Edited by pippo, 11 November 2014 - 06:49 AM.