Quote:
Originally Posted by Vanda
Don't truss designs suffer from dust/stray light more than enclosed tubes?  |
They can, but there are ways around this.
*One is designing the truss dob to minimise stray light.
*Useing a 'light shroud' to enclose the 'tube' when assembled- this is really only needed in a light polluted location. In a dark site, there really is no stray light around.
*Light baffels can be fitted to the mirror box and the secondary cage to reduce stray light. They act like lens shade on a camera lens.
Dust is no bigger problem than an open tube. Both will collect dust while they have their mirrors exposed. The inside of a solid tube gets really, really dirty over time, which acts a source of dust as it gets shaken off the inside of the tube, only to settle on the primary.
What truss dobs are more suceptible to is dew forming on the primary mirror. In an enclosed tube, the tube helps maintain the moist air away from the mirror much more effectively. Dew control heating can, and is readily added to truss dobs to stop this problem.
I can tell you from my experience, a 17.5" dob is much easier to transport as a truss dob than a solid tube scope! Man, is it ever! The truss dob in the process to finishing is the exact same scope in the solid tube pic. What ever 'problems' an open truss design may present, comes nowhere near the single problem of a big solid tube. Just finding a spot to store the sucker is a task in itself.
