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Carbon truss would be better. How much better? I don't know but possibly significantly.
All the top RC, CDK etc are carbon truss. Why? Firstly lighter weight. Secondly they have less tube currents from temperature differentials between the tube and the mirror and thirdly for stability of focus.
Carbon truss type or carbon tube type scopes do not shift focus much at all with temperature shifts.
Aluminium tubes match refractors quite well as the shrinkage of the tube when it gets colder is not too different to the shift in focal length of the objective - FSQ excepted.
But steel, probably not a good match. Perhaps others who own one of these steel tubed scopes can comment. Does it need to be refocused when temperature drops and is very sensitive to temperature drops. Some scopes are.
A heavier tube will affect your mount and ability to get round stars. How much weight can your mount take easily?
If the above is not a concern dew is no different for a steel tube versus a carbon truss as the carbon truss should take a material shroud that covers it. That also blocks stray light.
You could though wrap a steel tube with a thermal blanket to reduce the onset of dew more easily than a truss bit I suppose you could do the same on the truss.
Dew is handled in a few ways.
1. Dew heaters
2. Dew shield
3. Thermal blankets to delay the cooling of the tube to dew point and keep it a few degrees warmer when temps drop.
4. Fans
I would think the big factors would be weight and the affect that may have on your mounts tracking, the focus shift with temperature drops and the thermal currents inside the tube affecting image quality.
Greg.
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