Mounting a RACI finderscope on a collapsible tabletop telescope

I recently bought a Sky-Watcher Virtuoso GTi 150P tabletop 150mm (6-inch) telescope. This is a slightly larger variation, with a go-to mount, of a popular design sold by Astronomers Without Borders as the OneSky, a 130mm (5-inch) altitude-azimuth mounted collapsible tabletop telescope, shown at left.

These telescopes have a Vixen-style dovetail bar attached to the solid part of the tube—the green thing in the pictures of my telescope below. This is how the tube attaches to the mount, which has a Dobsonian style groundboard for the azimuth (side to side) axis and a half-fork with dovetail saddle for the altitude (up and down) axis. The tube can be removed from the saddle and clamped back on with a single threaded knob, the knob sticking up from the blue tube in the picture of the OneSky, making this portable design even more portable.

The problem

For finding objects, or in the case of the go-to model, aligning the mount or finding objects when the go-to isn't cutting it, the scopes are equipped with a straight-through red dot finder that projects a red dot on a window in front of the stars. A clever design with many variations, but like some people, I have trouble—no, make that pain—bending my neck enough to comfortably look through one, especially at objects high in the sky. 

On my other two scopes I have added azimuth circles and a digital angle gauge to find objects by looking up their alt-az coordinates in an app like Sky Safari Pro, moving the scope so that the coordinates are set on the azimuth circle and the gauge, and then using a right angle correct image (RACI) finderscope to zero in on the target. A RACI finder doesn’t require neck contortions and shows a correctly oriented view like you would see in binoculars.

I wanted to add a RACI finder to the Sky-Watcher tabletop telescope, but the problem is that the front ring that holds the secondary mirror and focuser is extended out on two truss tubes so that the whole front half can collapse into the solid rear half that holds the primary mirror, making it quite compact. There is no good place to add a finder on the front ring and it would make the scope quite front-heavy, requiring some sort of counterweight for manual operation. Others have added reinforcement to the front plastic ring or have drilled holes in the tube to add a finderscope, but I didn’t want to do either of these things. 

The solution

I added a universal dovetail shoe (base) to a block of wood attached to the scope's dovetail bar (the green thing) and swap my RACI finder between my 4.5-inch and this telescope. Looking at the design, the long dovetail bar attached to the telescope tube has two channels that run its length and a single 1/4-20 threaded hole close to the front end of the bar. The hole is presumably for mounting on a tripod, but it’s at a very poor location for balance. I had seen others mount a laser pointer and finder on that part of the dovetail bar, so I experimented with mounting a Svbony SV182 6x30 RACI finder that I have on my 4.5-inch reflector. I zip tied it in place to see how it worked. The problem was that, sticking out straight from the dovetail bar, the finder was too far from the observer’s position and I had to get up and either lean over or walk around the back of the scope to the other side to use it.

If I were to fasten a block of wood to the end of the dovetail bar at a 90 degree angle, then I could mount the RACI finder on the end of it, bringing the eyepiece to a much better position, even better than if I had drilled a couple of holes in the solid tube to mount it. After doing just that, I noted a post on the OneSky megathread on Cloudy Nights that did something similar, but by drilling and tapping a dovetail clamp instead of using a block of wood. Same end result.

Here’s how to do it

I cut all the pieces using a basic mitre box and a hand saw.

I cut a 5” piece of 2x2 baluster (vertical railing piece) that I had left over from making the legs for the telescope’s table mount. I cut a 45 degree corner on one end so I wouldn’t have a sharp corner sticking out. These balusters tend to vary slightly in cross section width, so I checked a few pieces before I found one where the dovetail finder shoe, or base, fits tightly in one direction—one more way to make it even more solid. Note: I used balusters rather than the 8’ lengths of 2x2 that they have because the balusters tend not to be as warped as the long pieces and they were actually cheaper per foot.

I glued and screwed two small pieces of wood to the block to sit in the bar channels and keep the block from rotating on the single bolt. I cut the two little pieces from a large size paint stirring stick (1/4” thick). The pieces are 7/16” wide and 2-1/4” long. I sanded them so they fit tightly into the bar channels.

This side will face the observer sitting at the telescope.

I dry fit the block and the two channel pieces to make sure they fit tightly in the dovetail bar. There are two screws in the dovetail bar at the bottom of each channel 1/8” from the front end of the bar. The block would need to sit behind these screws with the channel pieces butting up against them to add stability. I marked where the bolt would go through the block into the dovetail bar and also where I would need to glue the small channel pieces that would fit snugly into the two channels in the bar. I had cut them a little long just to give a bit more twist resistance in the channel.

Where the bolt would go through the block and screw into the dovetail bar, I countersank a 3/4” diameter hole about 3/16” deep, enough so the bolt head, with a 5/8” outer diameter - 1/4” inner diameter washer, would be flush or nearly flush with the surface, using a 3/4” Forstner bit. (3/4” because my wrench socket would fit in it so I could tighten the bolt.) You must do this before drilling the hole for the bolt so that the bit can center properly. It’s not essential to countersink the bolt head, but I thought it would be better than having it sticking out, and I recently got the Forstner bit set, so I’m eager to find reasons to use it! I then drilled a 1/4” hole all the way through the block, centered in the 3/4” countersunk hole.

I inserted the two little channel pieces into the channels and pushed them tight up against the screws in the bar channels. I inserted the bolt and tightened it to make sure the fit was good. Then I removed the bolt, put wood glue on the two channel pieces where they would join the block and bolted the block into place. Once the glue had dried for about 45 minutes, I removed the assembly and cleaned off some glue that got on the dovetail bar. It removes easily.

The dovetail shoe for the finder has four slots for screws. I screwed it into the top of the block with four 1-1/4” #6 wood screws. Everything looked good, so I took the shoe off the block assembly, painted the block assembly black, reattached the shoe, and attached the whole assembly to the dovetail bar. The shoe stays on the bar and the finderscope is removed for transport. This modification is also entirely reversible with no alteration to the telescope.

The finished mount. Note the four screws added to the channel bars. I found glue alone did not hold. Make sure you recess the screw heads into the wood with a countersink bit so they don't scrape the dovetail bar.

The finder is at a more comfortable, although still not optimum, location. I can also fit my head in there to use the red dot if necessary. The scope can rotate through the entire range of altitude motion without anything bumping or binding, but be careful when pointing above 50 degrees, as the additional weight of the finder will want to flip the tube backwards.

Packed up, the finder mount is out of the way and adds very little weight or volume to the overall package. Just loosen the two thumbscrews, slide the finderscope on, and tighten the thumbscrews. 

View from above when collapsed. The finderscope mount does not stick out beyond the round baseboard of the telescope mount. The dovetail shoe is mounted so that the thumbscrews point inward and are less likely to catch on a cover or other item.

Now I can use the RACI finder more easily and swap it between the two telescopes. It's still not an optimum viewing position especially at higher altitudes, although being able to rotate the diagonal on the finderscope helps. But for these collapsible telescopes, this makes a useful addition or alternative to the red dot finder.

Why does finding things easily have to be so hard?

In a previous post, I noted that I had gone over to the "Dark Side" and bought a 6-inch tabletop reflector with go-to, the ability to punch in an object and have the motor slew the telescope to it. This is a Sky-Watcher Virtuoso GTi 150P.

Well, so far I'm not impressed with the Dark Side. Like most tech gear, I have a love-hate relationship with it. I love it when it works. When it doesn't, which seems more and more of the time now, I hate it. I can't count the number of times just in the few weeks that I've had it that I wished I could just push the scope where I want it to go, like a manual dob. That always works. Always.

So what are the issues? For one thing, you need two suitable stars to do the initial alignment. These are selectable from a list. In a partly to mostly cloudy sky, which is common around here, two suitable stars may not both be visible at the same time. Understandably a limitation of the sky conditions. But if they are visible, the scope may slew many degrees away from the target star, so you need to choose only the brightest stars that are easiest to navigate to manually and recognize in the eyepiece as the correct star. 

Then there's the accuracy. Maybe because it's a cheaper mount (the scope retails for $470 and I paid even less on sale), but an initial alignment almost never lasts the whole observing session, which for me is usually between two and four hours. Sometimes, despite leveling, centering the alignment stars, and doing all the required tasks, the first object I punch in after alignment is still several degrees off. Occasionally it's right in the middle, but most of the time it's either on the edge if I'm lucky or somewhat outside a low power (30x) field of view. When it's several degrees off, I can starhop my way over to it with the help of the Sky Safari chart. Again, somewhat of a limitation of the technology.

Then there are the random take-offs. I'll have an object in view and then as I am watching, with the phone on the table, the scope suddenly decides it wants to look at something else and slews on its own. Hmm.

How about connection drop outs? This scope has WiFi, to which the Synscan app connects so you can control it with your phone. Synscan is very rudimentary in its interface for selecting objects (and the font for that function is inexplicably small). So I tried using Sky Safari to select and go-to the objects I want to look at. At first things were great, except that Synscan would drop the connection every 15 minutes unless it was in the foreground. Despite ensuring the Android settings would prevent this, it still did it. I could live with that. 

But then either Synscan or Sky Safari must have done an update (à la CrowdStrike), and Sky Safari would no longer connect: the Gray Screen of Death (GSOD) in the screenshot. So I used the apps separately, selecting an object in Sky Safari and pointing to it with Synscan, then going back and forth between apps to actually get it in the field. This is supposed to be the easy way of finding stuff? I later found that if I just move Synscan to the foreground and then back to Sky Safari, the latter will reconnect. But...really?

Lastly, I find that having to look down and press buttons on a cell phone when I'm observing is distracting and clunky. It also doesn't help with maintaining night vision, despite a "night mode" in the app, which is not well implemented. You can slew at different speeds, but it's aggravating to keep overshooting over and over. I tried the "tilt to slew" feature in Sky Safari, whereby you tilt your phone a little one way or the other and the scope slews in response. That is even more masochistic, no matter how slow I set it. Sometimes I give up, loosen the clamps on the axes, and just move it by hand. Always works. But that kind of defeats the purpose of go-to, doesn't it?

Well, by now you either think I'm a total crank, or maybe that go-to is not everything it's cracked up to be. In fact, I have come to the realization that both are true. 

I am now experimenting with using the free progressive web app Astrohopper as my "push-to" way of finding things (see my initial review on Astrohopper here). It works well for that purpose and is more reliable than the go-to. I can still use the tracking once I find an object, and that's my main reason for getting the go-to version over the non-go-to. I can't use straight-through finders anymore due to physical limitations, otherwise I'd still be starhopping, which is the simplest, most reliable, and most rewarding way to navigate with a telescope.

By the way, the scope itself is great. It's the tech part that could use some refining, to say the least. The Synscan Pro app gets a 2.2 star rating on Google Play. The non-pro version only gets 1.7 stars. I may end up staying with Astrohopper as my finding tool, then turn on the tracking. That works. [9/21/2024 Update: I got fed up with the go-to, and Astrohopper seems to not be able to geolocate after browser updates, so I added an azimuth circle to the scope base and use that and my digital angle gauge to navigate now. I only use the tracking, and that is often out of whack, but it's nice when it works. Maybe I'll write up how I did the azimuth circle in a future post.]

Snarling dog image by Albert Leung via Flickr (CC 2.0).

Make a table for a tabletop telescope

If you or your child are just getting started in visual astronomy, I can recommend a tabletop telescope of 4.5" to 6", such as the Sky-Watcher Heritage 150 Tabletop Dobsonian. This telescope (reviewed here) has good quality optics, is compact and portable, and very comfortable to observe with. But it's missing a table.

Why make one

You would think that a tabletop telescope is designed so that you can use whatever table you may have handy: a picnic table, a foldup table, a stool, or just a small end table. That may have been the intention, or maybe just the marketing, but when you’re looking at objects in powers of 30x, 50x, 100x, or 200x, you need something very stable so the view isn’t all shaky.

Picnic table? Nope. When you sit on it, you’re going to make it shake. It is also unlikely to be in the best spot for observing and you can’t move around the telescope.

Foldup table? Nope. Really shaky unless you get one that’s built like a tank, and that defeats the portability factor that is often the main advantage of the table.

Stool? Maybe, if it’s solid and the right height. You could cut the legs to size, but will it be large enough to fit the telescope? It may also be bulky if you have to transport your telescope to a remote location.

End table? Three legs will be better for leveling on uneven ground, and you have the same problems listed above as a stool.

Well, that’s a bummer. You thought a tabletop scope would be just the thing for portability. Now you’ve got one and no good table to put it on.

Fear not. Some people use a milk crate, build a simple tripod, or buy something at Ikea like this stool.

Or...and you knew this was coming...you could have fun and build your own observing table. It’s not hard (if I can do it!), and you can customize it for your own observing needs. Continue reading to achieve tabletop nirvana.

How to do it

The table I built for my Sky-Watcher Virtuoso GTi 150P, a 6-inch collapsible tabletop telescope, is simply a round piece of 1/2” plywood with holes drilled in it to hold eyepieces and three legs made out of cheap 2x2 lumber that can be unscrewed so the table top lies flat for transport. The legs are cut with about a 10 degree angle so they provide a little more stability than straight legs, although you could make them straight to simplify things even further. Each leg has a 1/4-20 hanger bolt screwed into one end which allows it to be screwed into a t-nut fastened in the tabletop. Easy-peasy, and it takes up very little room in the car if you unscrew the legs.

I started by making a circular cutting jig for my jigsaw since I don’t have a router, the preferable way to cut circles. If you don’t even have a jigsaw, you can buy an edge-glued round piece of wood (I recommend 18”), although some reviewers have said they sometimes come unglued or split.

The base of my scope is about 14" in diameter. I decided on an 18” diameter circle so I would have a couple inches around the outside to drill holes for eyepieces and to put my cell phones and filters down. I used 1/2” plywood to keep the table as light as possible. With the scope feet directly over the table legs, it only needs to be stiff enough to keep the legs in place without bearing the weight of the scope. [9/22/2024 Update: Because the go-to on my scope is unreliable, I added an azimuth circle to the base of the telescope. The circle sticks out about 3/4" all around, so I built a new table, this time using 3/4" plywood and making it 20" in diameter. I like it better, and I recommend you go with those dimensions. It's a little heavier, but not by much. It also makes a great camping side table when you're not observing.]

My mistake in cutting the plywood circle with the jig and jigsaw was I trusted in a YouTube video that showed how easy and neat it was to use a cutting jig. In reality, the saw blade wants to either go inside or outside the circle unless you watch very closely. I had the saw run outside the circle on one part and inside on another, breaking two blades. 

Were I to do it again, I would only cut a couple inches at a time and check to make sure it was still cutting on the circle. Or I would just draw the circle on the wood and cut it freehand with the jigsaw. I’ve done that before and it comes out fine. I just might not do it if I need the precision necessary for an altitude bearing, for example, but for this purpose it’s fine.

Once I had a pseudo-circle cut out, I marked where the three feet of the telescope would go. You can simply place the telescope base in the center and mark where the legs go. To be more precise, you can divide the circle into three sections by drawing a diameter (1), then drawing lines (2 and 3) the length of the radius (9” in this case) from the outer point of the first line (1) to where it intersects the outer edge of the circle on both sides, then drawing the other two lines (4 and 5), as in the diagram.

To make sure I had the scope centered, I partially screwed a wood screw into the top of the circle in the center. Some of these tabletop telescopes have a threaded hole in the center of the base. I just placed that over the screw and marked where the three feet would go.

If you don’t have the center of the circle marked, you can find it by drawing a chord at any point on the circle (line 1) and drawing a second line (line 2) from the midpoint of that line using a carpenter's square or other object that will give you a 90 degree angle. Repeat in a different location (lines 3 and 4) and where lines 2 and 4 cross is the center.

To screw in the table legs you can get angled leg brackets, but I don't like the inserts they use and I wanted a nice flush surface so I could slide the tabletop in between stuff in the car easily. So I put three 1/4-20 t-nuts where the feet would sit. These need to go in from the top of the table so that when you screw in the legs from the bottom, they will be pulled in tighter, rather than pulled out of the wood. Make sure the t-nut barrel is long enough to grab at least a few threads of the hanger bolts in the legs but doesn’t stick out the bottom if it is inset about 1/8” (see below). You want the legs to contact the table when screwed in tightly to give a nice stable grip.

I used a 3/4” Forstner bit in my cordless drill to first inset the holes about 1/8” in the top of the table where the t-nuts would go. I didn’t want to go too deep in 1/2” plywood, but if you use thicker plywood you can go deeper. You just want them inset to give some edge for the telescope feet to catch on so it won’t slide easily.

Then I drilled a hole in the center of each inset with a 9/32” regular drill bit. If you don’t have that size, use a bit that’s just slightly larger than 1/4” because the threaded barrel of the t-nut will be a little larger than 1/4”. Hammer in the t-nuts from the top side until they sit below the surface of the table.

I wanted some eyepiece holders, so I marked off three holes along the outer edge of the table top in each of the three sectors. Test the fit by placing the telescope on the table and your eyepieces where the holes will be. Make sure the telescope clears the eyepieces through its full rotation of 360 degrees. When satisfied it would, I drilled holes with a 1-1/4" hole saw.  I also added a 2" hole to each sector, even though my telescope doesn't have a 2" focuser. I figured I might want to use the table for stuff while using my 10-inch, and I have a couple of 2" eyepieces. It would also lessen the weight further. [8/28/24 update: I may redo the top without the 2" holes. Twice now I've almost dropped an eyepiece through the 2" hole onto the driveway, thinking it was the 1.25" hole. Oops.]

I sanded both sides and the edge of the table top with a random orbital sander and the holes manually with small pieces of sandpaper and a scrap piece of PVC pipe.

As noted above, you can just make the legs straight at whatever height you prefer if you don't want to take the extra steps to angle the legs, although you will sacrifice a little stability. 2x2 lumber is cheap and you can make several sets if you like. I like to use balusters, which are the vertical pieces in a deck railing, because they tend to be straighter than the 8’ lengths of 2x2. Those can be horribly warped and actually cost more per linear foot at my local store.

To make straight legs, drill a hole in the center of one end, as straight as possible, a little deeper than the length of the wood screw part of a 2" 1/4-20 hanger bolt. Use a drill bit a little smaller than 1/4” so the screw will have plenty of wood to bite and hold tight. Screw it in by threading two 1/4-20 nuts and tightening the upper nut with a 7/16” wrench until you get the length sticking out that will work with your t-nuts, roughly 3/8 to 1/2 inch. You can unscrew it if you overdid it by putting the wrench on the lower nut and twisting counterclockwise.

To make angled legs, which will add stability to the whole setup, I found an easy way is to take a typical mitre box and lay the uncut piece of 2x2 diagonally so that one side is up against the top of the box as seen from above and the other against the bottom. Clamp it down. If you cut along the 90 degree slot in the middle you’ll get about a 10 degree angled end. For the first and the last cut, you’ll have to estimate and just clamp the wood down. 

Cut three legs so the ends are all at parallel 10 degree angles, i.e., the piece looks like a parallelogram from the side. I cut my legs 10-5/8” long, which, with the 1/2” plywood top and the 10 degree angle, gives me a table top height of about 11 inches, just right for my adjustable observing chair at the height I like to sit.

Now put each leg in a vise if you have one, so that the angled face is horizontal. Then just drill your hole in the center vertically. Screw in the hanger bolts as described above using two 1/4-20 nuts and a 7/16” wrench. When you screw the leg into the table, the other end will trace a small circle, but it will work. 

I adjusted the depth of each screw so that the leg would screw in tight to a particular t-nut where it points outward, and just marked each pair with painter’s tape on the table and leg so I could easily match the leg to the hole. Later I’ll use a Sharpie once I’m sure everything fits well. You can always readjust the screw depths as things wear.

If you use outdoor plywood, you don’t really need to paint it because you're not going to leave it out in the rain, but I got a spray can of spar varnish and gave the table a few coats. A cheaper option would be paint. I recommend white so it's easy to see at night and you can see where to put your eyepieces. If you use treated wood for the legs, they don't need to be painted but you can paint them. If a few drops of water soak in, they are dry enough to be painted, otherwise wait a week or two for the chemical treatment to dry completely before painting. Use a tack cloth after sanding everything to remove any sawdust and grit.

Lastly, I put a piece of white duct tape on the table top at each point where the legs go to assist setting the scope on the table so the feet are directly over the t-nuts.

That’s it. If you mess up, all the parts are cheap and you can redo any or all of it. You can also make legs of different lengths if needed.

My Sky-Watcher Virtuoso GTi 150P tabletop telescope (same as the recommended scope at the beginning of this article but with an electronic mount) on the table I built for it. It looks happy, doesn't it?

[9/22/2024 Update]: Here's the new table I built to accomodate the addition of an azimuth circle to replace the go-to. I made all the eyepiece holes 1.25" and painted it white. 20" diameter using 3/4" plywood. The scope is even happier now!

Materials:

Piece of Plywood 1/2" to 3/4" thick big enough to cut a suitable sized circle (18" is usually good) or precut wood circle

One or two 2x2" stair balusters

Three 1/4-20 t-nuts, short enough not to stick out from the plywood, depending on the thickness

Three 2" x 1/4-20 hanger bolts

Two 1/4-20 hex nuts

Paint or varnish

Tools:

Mitre box and hand saw

Power drill with 9/32" (for t-nut holes),  1/8" or 3/16" bit (for hanger bolt holes), 3/4" Forstner bit, 1-1/4" hole saw

Jigsaw (unless you are buying a precut wood circle)

7/16" wrench

Sandpaper, sander (or sanding block), and dust mask (I like this one for sanding, painting, and gluing)

Tack cloth

Two bar clamps or C clamps large enough to clamp a 2x2 in your mitre box and to the workbench surface (which could be a piece of plywood laid over two saw horses if necessary).

Bench vise

Hammer (a big, short bolt helps to hammer the t-nuts below level so you don't damage the table surface)

Carpenter's Square or L-Square 

Pencil or X-acto knife (makes more precise measuring marks for cutting)

A simple dolly for moving a Dobsonian telescope from the garage or shed

Reader Pete suggested I write up something about my dob dolly pictured in the post on making the heavy 10-inch Dobsonian telescope more easily transportable. A dolly or hand truck is useful if you are using a heavy telescope at home or next to where it is stored, versus disassembling it and moving it by hand or transporting it to a dark sky site.

My home is around Bortle 8 (badly light polluted), but I still like to get the 10-inch dob out sometimes because it shows more in a light polluted sky than either my 4.5 inch or my new 6-inch reflector. So rather than heft the base and tube out onto the driveway every time I want to observe, I built a crude but effective flat dolly for it, as detailed below.

Option 1: buy a hand truck

If you don’t want to build a little dolly, you can simply buy a hand truck such as this one at Harbor Freight for somewhere between $50 and $100 and make a few minor modification to carry your Dobsonian. Usually this involves adding a plywood piece to make the toeplate larger (the flat part that the object sits on), adding padding for the scope tube about halfway up the frame, and a strap to hold the scope tube to the hand truck. 

In fact, this is what I am recommending for my brother who has a 6-inch Orion SkyQuest XT6. The scope is not very heavy, 31.5 lbs. total, but to get to a decent park in the city to observe he has to tote it about six blocks (he doesn't drive). Ugh. So a hand truck makes sense for him. Here’s a Cloudy Nights post that might give you some ideas.

Another advantage of a hand truck is that it's very useful around the house (toting bags of yard waste around, moving furniture, etc.).

Option 2: build a flat rolling dolly

Here’s how I built a very simple but also very crude rolling dolly for my 10-inch Dobsonian. Caveat- there are no handles, so I just push and pull on the scope base to move it. Also, mine has front and rear wheels that are different sizes because my driveway is on a three percent slope. This makes it level without any further adjustment so I can use my azimuth circle/digital angle gauge setup to find objects. Using a hand truck in this case would involve too much fuss and potential trouble. If your driveway or path is level or if you don’t need the scope to be level, you can use the same size wheels. If your driveway or path is not paved, or if you have to negotiate steps or anything taller than an inch or so, you are probably better off with a hand truck with 6” or larger wheels.

I had some scrap pieces of 5/8” roof sheathing plywood leftover from a roofing job. (Always see what your workers are throwing away and ask them to save it if you might find it useful.) The base of my 10-inch is a 22” diameter circle, so the dimensions are optimized for that.

I cut a 22” x 26” rectangle from the plywood. The extra 2 inches in front and back provide room to fasten the wheels on without getting in the way of the feet on the scope base or having the bolts sticking out and scraping the base.

I needed the front of the dolly to be 1” higher than the back to compensate for my sloped driveway. I bought a pair of 3” rubber rigid casters and a pair of 2” rubber swivel casters at Harbor Freight. These are 3-5/8” and 2-5/8” high, respectively, which gave me the just about the right adjustment for my sloped driveway. I thought about getting casters with brake levers on them, but these aren't strong enough to hold anything on a slope, just keep it from rolling on a level floor. The casters bolt through the plywood with four bolts each. You’ll need a drill and a pair of wrenches. Make sure you buy bolts that fit the caster holes.

I was able to put the nuts on the bottom of the fixed casters, but the swivel casters were smaller and the threaded bolt ends sticking up would have prevented them from swiveling, so I had to have them sticking up on the upper side of the plywood. It’s not optimal, but that’s what I had to do.

With an azimuth circle on the dob base, I wanted to make it easy to align with the cardinal directions, so I put a mark on the dob ground board that would align with a mark on the dolly to position the base so it would be roughly aligned in azimuth and I would just need to fine tune it each session.

I put the scope base where I would be placing it on the plywood and painted a white circle all the way around on the dolly’s surface to help me align it when plunking it down. 

To keep the base from sliding around, because I would be pushing and pulling it, I glued pieces of wood just outside each dob foot. Normally dobs have three feet, but I found adding three more feet from wood made it more stable on uneven ground, so I have six little pieces of wood glued to the dolly. Just make sure they are shorter than the dob feet so they don’t touch the ground board.

That’s pretty much it. I didn’t even waste paint on it, since it will be spending most of the time in my garage, and paint is often one of the more costly parts of any woodworking project.

So how well does it work?

My only real complaint is that it’s a little hard to maneuver with the two swivel wheels, so I just have to go slowly when pulling/pushing it in and out of the garage. To keep the scope from rolling down into the street, I use a rubber wheel chock from Harbor Freight and a rubber sanding block under each front wheel. If you use something different, make sure it's not going to just slide down the slope. I always stand on the downhill side of the scope when rolling it to and from the driveway.

If you have to roll the scope over a threshold, for example I have a 1” bump from my driveway into the garage, use a piece of baseboard molding a bit longer than the width of the dolly. It has a tapered profile that works nicely as a little ramp. Tip: Save some pieces of any molding you replace. I’ve found multiple uses for this.

Just be aware that you’ll be adding about 4” or so to the height of the eyepiece when observing. Even my adjustable observing chair needs a booster cushion at its highest adjustment for some positions when the scope is on the dolly. I don’t notice any instability or shaking in the views from being on the dolly.

If you have a telescope on a heavy tripod and mount and want to build a dolly, here's an article from BBC Sky at Night that might give you some ideas.

Bonus Tip: If you have a store like Harbor Freight or Northern Tool near you, or can order from one, you can save a lot of money on many items, including tools that you’ll only use occasionally. Better to have the right cheap tool than the wrong high quality tool. I don’t have any affiliation with them, I just like to save money if I can.

I have gone over to the Dark Side

For most of my observing “career,” I have starhopped to objects, later replacing a straight-through finderscope with an azimuth circle on the dob ground board, a digital angle gauge for altitude, an app for the alt-az coordinates of objects, and a right angle/correct image (RACI) finder to find things when my neck just couldn’t take the contortions of a straight-through finder anymore.

Well, that has been working fine, but I decided I needed a downsized scope for when I can’t handle the 10-inch dob. Enter the Sky-Watcher Virtuoso GTi 150 Tabletop Go-To Dobsonian.

Wait...what? Go-to?

Yep, I have gone to the Dark Side.

I did way too much research (although I had a lot of fun doing it), and finally settled on a 6-inch tabletop scope. This is my first new scope in 20 years. I’m an adherent to the philosophy that you really can’t beat aperture to see things better, so after much hemming and hawing I ruled out refractors, at least for now. A 6-inch refractor is huge, heavy, and very expensive. I also ruled out catadioptric scopes due to the total price per inch of aperture and the longer focal lengths with correspondingly narrower fields of view. I also don't want to see things mirror-reversed after looking at them for 30 years in correct orientation (albeit rotated 180 degrees).

I could have gotten a 6 or even 8-inch standard solid tube Dobsonian, but I kept thinking how nice it would be to have tracking, where the telescope’s motor tracks the object you are looking at so you don’t have to keep resetting the telescope as the Earth rotates. This is particularly nice during outreach events where you have a lot of people taking turns looking in the eyepiece. And I wanted to keep the weight and bulk down.

My choice for a downsized scope

I settled on the Sky-Watcher Virtuoso GTi 150P. I figured if I have to give up some aperture, I can at least add go-to and tracking to compensate a bit. This telescope is a member of the "tabletop Dobsonian” family, really a half-fork mount hybrid. Other telescopes of this type include the very popular OneSky from Astronomers Without Borders (see the megathread on Cloudy Nights), the Zhumell Z130, the Orion Starblast, and the Sky-Watcher Heritage, with models available in 114mm (4.5-inch), 130mm (5-inch) and 150mm (6-inch). When in doubt, my advice is to take the larger aperture when possible. The Virtuoso GTi is the only one with a go-to mount at this time.

This particular scope has a roughly 14-inch diameter base, a 16-inch tube when collapsed (27 inches when extended), and weighs a total of 19 lbs., which is 49 lbs. lighter than my 10-inch and a whole lot more compact. Now that's downsizing!

I’ve had the scope out in the Redneck Observatory a few times and to my regular semi-dark site a couple of times. It’s taking a bit of effort to get used to the go-to, which doesn’t always seem to play well with my Android phone, but when it does, it’s pretty cool. I do love the tracking. The phone disconnects every 15 minutes from the scope’s WiFi unless the Synscan app is in the foreground, and I’ve tried every tip from users to no avail. Eh, not a biggie, but still annoying.

After trying to control the scope through Sky Safari Pro with its “tilt to slew” feature and constantly overshooting the target, I decided to just use the Synscan app to center objects after the initial go-to movement done through Sky Safari Pro. I dial the slew speed down to 3 in Synscan and it works pretty well. I have had it sometimes just start slewing off the object on its own, but I'm not sure that isn't user error. I still say it’s a whole lot easier and a lot less frustrating just to push a non-go-to dob around manually to find stuff.

The scope retails for $470 currently when not on sale, which is a pretty good price for a 6-inch mirror, go-to, and tracking. It will even resume tracking if you disengage the motor to manually move it around and then reengage, what they call "Freedom Find," using dual encoders. More important, the optics are good. Most important, it's fun!

As with any inexpensive telescope, there are suggested mods. Of course you’ll need a table to put it on, one that is stable. I built an 18-inch round table out of a scrap of 1/2-inch plywood and three legs from 2x2s screwed into t-nuts so I can break it down flat. A popular solution is the Super Simple 2x4 Tripod for Tabletop Telescopes if you want to stand and observe. If you don't want to build your own, some people recommend this stool or this table from Ikea.

The helical focuser also has some play in it, which has several potential solutions. The one I implemented was putting a 2-inch hose clamp around the top of the focuser housing and tightening just enough to take out the play. I also smeared some lip balm on the threads. I really like it now. I find I can use my Svbony 7-21mm zoom eyepiece no problem without any twisting and shouting. My Baader Hyperion zoom sits all the way down in the focuser to the point where the thumbscrews holding it in rub against the bottom edge of the eyepiece housing, but it works, and it's a better eyepiece than the Svbony (also a lot more expensive). [Edit: I added an O-ring to the barrel of the Hyperion and it no longer scrapes.] I also constructed a light shroud out of black craft foam, because with the upper assembly extended on two truss tubes there is no protection from light and dew, both common in my neck of the woods.

Added a light shroud and 11" high tripod table.

The main problem for me, aside from these quirks, is the red dot finder, which is a very cheap plastic thing mounted very close to the tube circumference. My neck just can’t take straight through finders anymore, but fortunately you only need it for initial alignment, although I have found I sometimes need to align it a couple of times during the night when it decides to go off somewhere on its own instead of where I tell it to go.

To solve the finder issue, I zip-tied a dovetail base for my right angle correct image Svbony SV182 finder that normally lives on my Tasco 4.5-inch to the end of the green dovetail bar. Not optimal placement, but about the only place it can go on this design, and it works without messing up the balance. I just need to get up out of my seat to look through it. In regular star hopping use this would be unacceptable, but for alignment it works okay. I might make a more permanent mounting piece out of wood. There is a 1/4-20 tapped hole there so I wouldn't even need to drill any holes in the tube.

RACI finder mounted on the end of the dovetail
(green) with a zip tie.

I opted for a reflector over a "cat." Kitty was not 
amused, but seems over it.

I’ll post updates as I get more used to this thing of the Dark Side. In the meantime, I have made a mod to my 10-inch manual dob so I can keep using that, too, despite my deteriorating physical condition.

7/19/24 update: If you have an Aldi store nearby, the Easy Home Collapsible Hamper makes a great cover for this scope. Turn it upside down and it's the perfect height. Also keeps its shape.

8/31/24 update: See my post Why does finding things easily have to be so hard? for my issues with the go-to and tracking on this scope.

Making a heavy dob base more manageable: divide and conquer!

The problem

I’ve had my 10-inch solid tube Dobsonian telescope, a Hardin "Deep Space Hunter" made by Guan Sheng Optical (GSO), for 20 years now and it has served me well. In fact, it’s doing better than my own body at this point. I’ve found it harder to load it in and out of the car to get to my darker sky sites. I needed to make it easier.

The solution

I can’t do much about the tube, which weighs about 32 lbs., but a post on Cloudy Nights got the neurons firing in my brain. It showed what one amateur astronomer did with the base of his 12-inch, and I decided to try it on my 10-inch.

The base is made of particle board and weighs about 38 lbs. It's heavy and awkward to get into the car. What if I could split it into two pieces that could be easily reassembled? That’s the idea, and it works! I separated the two round ground boards as one section, actually the round bottom of the rocker box and the ground board, from the rocker box as the other section. These are shown in the pink boxes below. These two sections were originally put together with six long wood screws coming up from underneath the rocker box bottom and into the bottom edges of the rocker box (indicated by the blue arrow below). The pink boxes denote the sections that would be separated:

 

To reassemble the two sections, I bolted two aluminum angles to the inside of each side of the rocker box and fastened them to the round rocker box bottom with four knobs inserted into holes drilled in the horizontal leg of each angle and screwed into t-nuts inserted in the underside of the rocker box bottom.

Inside the rocker box, showing the first angle
fully assembled. The knobs will be used to disassemble
 and reassemble the base.

The outside of the rocker box, showing the
bolts holding the angle. These will stay put.

The whole project took one afternoon, and was only complicated by the fact that I had replaced the original “lazy Susan” azimuth bearing (as shown in the diagram above) with Teflon pads riding on Ebony Star Formica (alas, no longer available). The pads would be in the way of the holes for the knobs, so I had to relocate them closer to the center. Telescope makers will tell you the pads should be located directly over the feet, but I found that in this scope it caused too much friction, so I had located the pads about a third of the way in from the edges, and the azimuth bearing was a lot smoother. Moving them further in would be pushing it, but it actually moves even more smoothly now.

The base is now easy to disassemble and reassemble.

Fully assembled. (The scope sits on a plywood
 dolly I made to make it easy to roll out on the
 driveway when I set up my Redneck Observatory.)

The rocker box now fits around
the tube in the car, saving much-
needed space.

How to do it

If you try this at home, think carefully about where you will put all the holes and measure everything precisely. I had to dodge the holes in the rocker sides from the original wood screws, make sure the knobs didn’t intersect with the circular path of the Teflon pads, avoid a pipe that I installed that holds a swivel table, and leave room to turn the knobs. It was a tight fit, but it works.

The tools and materials I used:

Materials (links to the ones I used):

Two aluminum angles, 1/4” thick, 2” legs (that turned out to be 1-3/4” in reality), and 12” lengths (that were actually 11-5/8”, although they were 1/4" thick, as advertised).

Four male knobs with 1” 1/4-20 threads. (3/4” might have been better- fewer turns needed as long as they reached the threads of the t-nuts.)

Four t-nuts (1/4-20 x 7/16 length); epoxy 

Eight 1-1/2" 1/4-20 bolts, eight 1/4-20 nylon lock nuts, 24 1/4” ID - 3/4” OD flat washers

Tools:

Cordless drill with 1/16”, 1/4”, and 5/16” drill bits, and one 3/4” Forstner bit

Hammer and short thick rusty bolt for hammering in the t-nuts below flush

Two 6” quick-release clamps

Metal file and sandpaper to round the sharp edges of the aluminum angles.

Hand vacuum to keep the aluminum shavings from getting everywhere

Process (for my particular dob, but most should be similar):

Caution! Aluminum angle edges may be extremely sharp. File and sand them before working with them.

Measure and plan where you are going to position the angles and drill all the holes. Do it a few times and set the angles, bolts, and nuts in position to see if there will be any issues before you start drilling. Mark the drill points clearly in pencil on the angles.

Disassemble and then reassemble the rocker box and round rocker box bottom, leaving the round ground board off. You will need to drill in the botton of the round rocker box bottom piece.

Cut the angles if needed (with a metal hacksaw), file any sharp edges that will be exposed, and clamp to the rocker box sides. In my case, there is a front stiffener board that precluded clamping on that end, so I found a piece of wood that fit tightly inside between the two angles that kept the front ends pressed against the sides. Improvise as needed.

I found it easier to do one side first, then the other.

Using a small drill bit, 1/16” or so, drill pilot holes for the two knobs from above, through the angle and the round rocker box bottom. (I did each hole one at a time.) You need to keep these holes small because the Forstner bit you will use to inset the t-nuts on the underside of the rocker box bottom needs to be able to center and it can’t do so with a larger hole drilled through.

Turn the assembly on its side and use the 3/4” Forstner bit to inset the two holes about 1/8”. This ensures that the t-nuts won’t stick out and scrape the ground board surface. I found later that the t-nuts don't hold well in the particle board, only an issue when the base is disassembled, so I epoxied them in.

T-nut epoxied and hammered into place on the
underside of the rocker box bottom. Note the
1/8" recess cut using a 3/4" Forstner bit.

Turn the assembly upright again and drill out the two holes with a 1/4” bit, all the way through.

Turn the assembly on its side again and widen the centers of the t-nut insets with a 5/16” bit.

Hammer a t-nut partially in, then fit the knob from the other side and make sure they meet up properly and there is no binding. I had to use the Forstner bit to widen the sides for several of the holes due to, ahem, user error, but got them all working. Once they line up, coat them with epoxy, being careful not to get any into the threaded tube, and hammer the t-nuts all the way in so they are below the level of the bearing surface.

Turn the assembly upright again and once both knob holes are drilled, screw in the knobs tightly.

With the sides still clamped/braced to the angles, drill small (1/6”) pilot holes horizontally through the angles and the sides from inside (aluminum first) to outside. Widen the holes with a 1/4” bit and insert the bolts from the outside with flat washers and put the nylon lock nuts with flat washers on the inside (aluminum surface).

Before assembling the base to the ground board, a little trick for Teflon bearings is to rub a bar of soap on the bearing surface that contacts the Teflon to give it a little more smoothness.

Once you are done, remove the original wood screws holding the rocker box to the ground boards, assemble the base with the knobs, and test the fully assembled telescope for function.

Now when you have to transport the telescope, you only have four knobs to separate and reassemble the two parts of the base, which is no longer a heavy, ungainly bulk. In fact, you should be able to cradle the rocker box around the bottom of the tube to save space in your vehicle, as in the image above.

What if you want a 10-inch solid tube dob, but don't want to mess with this mod?

All dobs are not created equal. If you are in the market for a lighter weight basic Dobsonian, consider the Orion Sky Quest series. Now that they are apparently made by Jinghua Optical Corporation (JOC), they are even lighter than the Synta-made scopes, and are the lightest mass-produced solid tube basic dobs I have come across. For example, the XT 10 has a 24.2 lb. tube, a 21.5 lb base, for a total of 46 lbs. In contrast, an Apertura AD10, made by Guan Sheng Optical (GSO), has a 34.8 lb. tube, a 31.4 lb. base, for a total of 66.2 lbs., a difference of 20.2 lbs. for the same size aperture! [7-12-24 update: Orion's parent company has closed up, so Orion may not be around much longer. If you're interested, make your decision quickly. 7-19-24 update: Looks like Orion is belly up. Maybe another company will supply the XT10s under a different name??]