A tabletop dobsonian is a great inexpensive but capable and portable telescope. The mount is a single arm hybrid dob base. The basic ones can be disassembled for air travel, and reassembled at the destination with a screwdriver, but you still have to have a suitable table at your destination to set it on.
However, the scope that I have, the Sky-Watcher Heritage GTi 150P (6-inch), has an electronic go-to mount that I would be very hesitant to try to take apart and reassemble. It's too big to fit in an average suitcase, but I wanted to take the telescope on a dark sky vacation via airline. What to do?
The optical tube assembly (OTA) can go in a 22-inch carry-on hard shell roller suitcase as long as it's well packed. The base that I built, consisting of a mount and table or tripod, would need to be disassembled to fit in a checked suitcase. I have a 26" roller suitcase that I used for this.
The total weight of OTA, mount, and table is about 25 lbs.
While you may not want or need to build this entire table mount, I hope this will give you some ideas if you are putting together your own travel setup.
Why not a tripod?
Some people use a sturdy photo tripod for their travel scopes, such as the
Innorel RT90C, a carbon fiber tripod that is often recommended for light travel scopes. I have a few problems with that, though. First, I don't like standing when observing, which would be the case if mounting my 6-inch Newtonian on one. It gets tiring very quickly if you're out observing for several hours or more, and it's difficult to keep your eye steady at the eyepiece when standing. Second, I was concerned with the stability. Third, and you knew this was coming, a good, light tripod is not inexpensive, especially after buying a mount to put on it.
Choosing the mount
I decided I would buy a lightweight mount and build a custom table for it. I chose the
Svbony SV225 alt-az mount. It's relatively inexpensive and sold without a tripod. It handles the 10 lb. weight of the 6-inch tube with accessories very well. The SV225 is just over 5 lbs, so it's the heaviest piece of the table mount, but still quite manageable for air travel. The motions are smooth and the slow motion controls partly make up for the tracking I'd be missing by not having the go-to mount.
I chose not to adapt my existing table for the mount because I wanted to save a bit of weight and would also need to raise the mount so that the mirror end of the tube would clear the table when pointed at the zenith. With a spacer block raising it thus, the eyepiece still sits 2-1/2 " lower than with the stock Virtuoso GTi go-to mount. Also, at 20" in diameter, my existing table would not fit in the suitcase. Case closed.
Building the table
Instead, I built a new table out of 3/4" pine plywood in a triangle shape with the corners cut off, a pretty common design to save weight. for the center spacer block I used two pieces of 3/4" plywood and one piece of 1/4" plywood. This raises the mount just enough, 1-3/4", for the mirror end of the scope, including the adjustment screws, to clear the table at the zenith. The block is on the left in the image. The edges of the top pieces are rounded to provide clearance for the OTA.
I inset 1/4-20 T-nuts into the top of the table, same as my previous tables. The legs have hanger bolts screwed into one end, so they just screw into the T-nuts from underneath. See
my previous article on building a table for details. The paper azimuth circle is glued to the tabletop with contact cement and sprayed with a clear matte sealer.
Making the table triangular instead of round allows for a wider footprint for the three legs for greater stability, with a smaller width to fit in the suitcase. Instead of the corresponding circle's diameter, the width of the table is the measurement from the center of one side to the opposite corner, which is further decreased by nipping off the corners. So a triangle cut from a theoretical circle of a larger diameter can fit where that same circle wouldn't, if you follow me. Basically, you have three legs at the same distance as you would for the circle, but with a smaller width for packing (reduced by the width of the blue arrow in the diagram). I cut the triangle from a theoretical 20" circle. The width in green is 15-1/2", so I reduced it by the 4-1/2" in blue by making it a triangle with cutoff corners.
The problem with a typical alt-az mount like the SV225 is that it must be mounted in the center of the table, which then puts the center of gravity of the scope well away from center and makes it easier to tip over, especially when the back of the scope is positioned over a side without a leg immediately behind it. This would be the same if it were mounted on a tripod. To account for this, I angled the legs a little more this time, about 15 degrees versus 10 degrees, to make a larger footprint and give it more stability. The legs are also a little longer to make up for the difference in height of the go-to mount versus the SV225. I made the legs out of 2x2 balusters, just like my other table. They screw into T-nuts hammered into holes in the tabletop 13-1/2" apart.
While it is more stable, it's still not as stable as I would like. The solution is to add weight below the mount. Yet I wanted to keep it light for travel. I'll get to the that in a minute.
The hardest part of this project was figuring out how to cut the triangular tabletop out of a piece of plywood without first cutting a circle and wasting a lot of the wood. After wrestling with the geometry of it all, I finally figured it out and made the cuts. Whew, I don't like my brain to have to work that hard.
Back to adding the weight for stability. Since I had my original 18" tabletop made from 1/2" plywood that had eyepiece holder holes already drilled into it, I decided it would make a great lower level rack for the table. Not only would it help stabilize the legs, but it would also provide a place to put a large rock (or bag of rocks, or some other "found" objects). Weight really does wonders for the stability of tripods, which is why they sell stone bags for them. Same for this arrangement. It would also give me a place to put eyepieces while observing, since the small amount of clearance of the OTA over the tabletop would not allow for storing eyepieces in holes there. It just fits in my 26" suitcase.
The next problem was how to attach this 18" circular eyepiece/weight rack to the three table legs below the main tabletop. I solved this by wrapping a cam buckle strap around the outside of the legs (the orange strap visible in the image above). The circular board sits nicely on the strap, leaving the eyepiece holes clear. Easy to set up and break down with no tools, screws, bolts or nuts.
I don't use straight-through finders, so I have a right angle correct image
(RACI) finder mounted on the OTA's dovetail bar. I've been adding azimuth circles to all of my scopes, so I added one to this table, too, printing an 8" outer diameter circle from
Blocklayer.com. See my
article on adding an azimuth circle for details. I use the same magnetic digital angle gauge for all of them. The azimuth pointer is a long strip about 1/2" wide cut from a piece of
aluminum roof flashing. It had to reach from the rotating top part of the SV225 base down to the tabletop, while clearing the spacer block. I attached it to the SV225 with Velcro so it is movable when aligning the table mount in azimuth at the beginning of an observing session. The SV225 has altitude and azimuth scales (the black circle below the slow motion cable in the image), but they are very small and pretty much impossible to view while observing.
The legs are 14-1/4" long, cut from
2x2 treated deck balusters, with the ends cut at 15 degree angles. I used a cheap plastic protractor to mark the angles and a mitre box with bar clamps to cut them with a hand saw. This puts the table height at 14-5/8" and the max eyepiece height around 42".
The whole table mount setup breaks down and fits with a bunch of other gear in a 26" suitcase. I do set the arm of the SV225 in the more compact position that it came shipped in, and that requires an Allen wrench that comes with the mount. I also need a small socket wrench with a 3/8" socket to remove the 3/8" center bolt holding the mount and spacer block to the table. It screws in from underneath. This is not something I would want to do every night, but for air travel to and from my destination it's fine.
Finding a suitable chair
You really have to consider everything when traveling for astronomy. One of the biggest issues was not having a suitable observing chair. Regular folding chairs are too big and heavy for a suitcase. The place I was staying at didn't have any suitable chairs. I normally use a
Denver style adjustable observing chair, but an adjustable chair isn't necessary for a scope this small and there's no way I would try to take one on a plane. So I found a
small folding tripod chair with the sitting height that I wanted, and added a round stool cushion, fastened to the seat with sheet stays, as well as tennis balls to the legs so it wouldn't sink into soft ground. The stool is only 1.4 lbs. and folds up to into a 17" bag. It's going to be great for short sits while birding and hiking, too (minus the cushion and tennis balls).
