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Hi all,
for those interested in design details, I would like to share with you a small but very important difference between classic design and UC design regarding the position of the collimation screws on the upper (according to position at zenith) and lower bar of the mirror cell.
Maybe you noticed that for UC, the upper bar has only one collimation screw whereas there are two for classic design and vice versa for the lower bar.
According to the mechanical engineer who designed the ?, the upper bar will be slightly more deformed at zenith than the lower bar because of the two spaced anchor points of the collimation screws at the lower bar. This will induce a mirror cell looking slightly at the back of the scope at zenith. Let us suppose that you collimate in this position, when the scope points at horizon, this effect on the primary cel will vanish (the primary is essentially carried by the sling) but another effect will compensate ie the flexure of the truss tube that will displace the secondary in the same direction, keeping the respective position of the two mirrors more or less unchanged. In the case of the classic design where the upper bar has two collimation screws, the two effects add. In the example of the cruxis telescope (a 1m diameter telescope) the computation shows that the two effects nearly compensate perfectly.
What is interesting here is that Dave K. changed the design (on purpose?) and that UC that have longer truss tubes with more flexure at low altitudes offer some natural compensation of the flexure with the specific position of the collimation screws on the mirror cell bars.?I am curious to know whether Dave K. decided to adapt the design on purpose or for another reason like the fact that this two collimation screws on the lower bar need less clearance when the VMB moves in the rocker box.

Regarding collimation, I am convinced that the UC22 with 8 truss tubes offering a strong anchor point almost below the focuser on the single ring UTA shows a better resistance to the flexure of the UTA when you move from horizon to zenith compared to the 6 truss tubes design of the UC18. I have a UC22 and a classic 15 (with short truss tubes) and I do not notice significant difference among the two scopes regarding to collimation stability between horizon and zenith.
Useless (as we do not build telescopes) but interesting to me and I hope some of you.?

Clear skies Frédéric.

Clear skies, Frédéric