Meet Leah: this 16-inch reflector is a marvel of craftsmanship and engineering.
A professional electrical engineer and hobbyist woodworker, Tom was up for something more challenging than a plain-jane Dobsonian for his first scope. "After searching the internet for ideas, I found a few images of the split-ring design," he recalls. "It had that cool look I was going for and offers the advantage of being a true equatorial mount." This was important because he wanted an instrument that would be suited to computerized pointing and tracking. Of course, such a mount is considerably more complex and difficult to build than a Dob; doubly so for a first-time builder.
To ensure that he understood the design in detail, Tom built a 1/4-scale model as a first step. This exercise demonstrated a few important consequences of the splitring configuration. As Tom recalls, "while playing with the model, I realized that the eyepiece could not remain fixed and needs to be able to rotate to any side of the tube." The model also showed that the mount's bearings would have to cope with both radial and axial forces, and that a traditional Dobsonian-style sling mount used for supporting the primary mirror wouldn't suffice for all the scope's various orientations.
To solve the first of these issues, Tom decided to equip Leah with a rotating upper cage so that the eyepiece could easily be orientated to the most comfortable viewing angle. "For the upper cage assembly, I settled on thin, interlocking rings of plywood kept in position by small rollers originally made for a sliding shower door," Tom says. One of the cage's best features is that the rotation is friction-controlled--there's no need to clamp or unclamp anything to change the eyepiece position.
Leah's 2-inch-thick, 16-inch f/4.2 primary mirror sits on a conventional 18-point flotation cell. Nothing unusual about that. What is clever, though, is how the mirror is supported laterally. Instead of a Dobsonian's single sling, Tom's cell incorporates what he calls a "quad sling system"--essentially four individual slings arrayed around the mirror's circumference. Each one supports part of the load in turn as the orientation of the scope changes. Turnbuckles allow the tension of all four slings to be adjusted and ensure the mirror remains exactly centered in the cell.
Critical to the scope's success was the quality of the bearings used in the mount. Tom's initial choice of gokart axle bearings proved to be unsuitable. In the end he opted for heavy-duty units he found on an internet surplus site. "It took some time to rebuild the mount to accommodate the new bearings, but wow was it worth it!" he says. With the scope moving smoothly, the next step was to add motors for go-to pointing and tracking. Each axis utilizes a servo motor assembly and encoder, along with a controller unit and wireless hand pad--all sourced from Sidereal Technology (siderealtechnology.com). He chose Software Bisque's TheSkyX Serious Astronomer Edition software to aim the scope. "The intricacies of gearing, clutches, and getting it all mounted probably consumed more time than any other phase of this project," he notes. "But to my surprise, the scope moved at my command the very first time I pushed the buttons!"
Tom is passionate about the technology behind Leah--indeed, for him it's one of the main attractions of amateur astronomy. "However, I still enjoy the great views the scope offers," he says. "One night at a recent star party, I was looking at the Swan Nebula and was amazed by the sharpness of the image and by how much it looked just like a swan. There is so much to see. Leah and I plan to venture out every chance we get."
Readers interested in learning more can e-mail Tom at firstname.lastname@example.org.
Contributing editor Gary Seronik is an experienced telescope maker and observer. Contact him about your own ATM projects via his website, garyseronik.com.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Telescope Workshop|
|Publication:||Sky & Telescope|
|Date:||Oct 1, 2015|
|Previous Article:||Secrets of nightscape photography: here are some essential tips for shooting the night sky above picturesque landscape.|
|Next Article:||The great watering hole: what have, we lost with the dilution of sci.astro.amateur?|