Build an air travel table mount for a tabletop dobsonian

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).

This setup worked great on my trip to Arizona Sky Village, and my brother and I were really glad to have the 6-inch along!

Upgrading from starter eyepieces

Beginner telescopes come with very basic eyepieces to get you started as soon as you open the box. Sometimes these are pretty decent and will work for you for a long time and sometimes they suck, but most people want to upgrade at some point. Unfortunately, many people now tend to upgrade too much, too soon.

My recommendation is to get an inexpensive zoom eyepiece to go with your new telescope. There are quite a few under $100 that are available. Even though I have a nice Baader Hyperion 8-24x zoom, this year I purchased a Svbony SV135 7-21mm zoom. It's a lot lighter, about six times cheaper, and a decent performer, getting mostly good reviews on Cloudy Nights for its price, and I agree. I got one for my brother, too, and he loves it. [Note: If you wear glasses or want a slightly wider view, you might want to go with the Svbony SV191 7.2-21.6mm zoom, which is a bit more expensive and not quite as sharp.]

With a zoom, you will get a feel for how different objects in the sky look in various eyepiece focal lengths, which determine the power, and what works best in your telescope. (Telescope focal length ÷ eyepiece focal length = power. For example, a telescope with a 750mm focal length with a 10mm eyepiece in it will give you 75x.) If you do eventually upgrade your eyepieces, after you get to know the sky better and know what you like to look at, you can keep the zoom and use it when you want to travel light, for quick sessions, planetary and lunar detail, double stars, and for outreach. That's what I do.

Zoom eyepieces like the SV135 have a narrower field of view than many comparably priced eyepieces and generally aren't quite as sharp or well corrected for aberrations, although this one does tolerably well. By twisting the barrel, you are able to zoom into exactly the desired power, replacing a large set of eyepieces with just one. 

As you progress, you might want wider or sharper views, which come at a cost. Televue eyepieces, the premier example of consistently high end eyepieces, are expensive because they give you well-corrected wide views, which don't come cheap. But a relatively cheap zoom allows you to experiment with different powers on different objects so you can find what works best in your telescope for you. Then you have a better idea of what you want if you decide to upgrade. This also allows you to take full advantage of your new telescope immediately. 

Well, maybe not immediately. More critical than upgrading eyepieces is learning the sky and how to find things in it with your telescope. See the Space Walk Among the Stars sound guides, which will help you find some wonderful deep space objects, as well as posts on determining directions in your telescope, how to set up your telescope for starhopping, the Astrohopper app, and others. 

The internet is full of observing guides. I would start by visiting the Sky & Telescope site, with their Interactive Sky Chart and lots of information for beginners. You'll find tons of information there. Also visit Cloudy Nights, the premier amateur astronomy forum. The Beginners Forum will keep you occupied for many cloudy nights to come and provide a place to ask questions.

Left: Screenshot from Sky Safari Pro. Apps like this help you locate objects in the night sky and can even control your telescope if it is go-to equipped.

Add an azimuth circle to a your Dobsonian and ditch that straight-through finder

A couple of years ago I added azimuth circles to the bases of my two Dobsonian telescopes, and recently added one to a go-to tabletop dob to replace the often unreliable go-to system. Coupled with a digital angle gauge, available in hardware stores or online for about $20-30, this allows me to dial in the altitude and azimuth coordinates for any object, creating a "push-to" system. I can literally find anything anywhere now without straining to look through a straight-through finder, as long as I can see it in my scope and it's included in my sky charting app. 

The main advantages are:

• No neck strain looking through a straight-through finderscope or red-dot finder (this was the impetus for me)
• Ability to find objects in areas of sky without a lot of bright stars for starhopping, or in light pollution
• Quick and easily repeatable
• No finicky and power-hungry electronics (the angle gauge takes two AA batteries that last a long time)
• Inexpensive

What you need and how you use it

You will need an app to look up the alt-az coordinates for an object in real time. As the earth rotates, these coordinates constantly change, and are based on your location and time. As always, I recommend Sky Safari Pro (Android or iOS) as a great all-round app that will list the coordinates and show you the star field once you've gotten close to an object. Even the Basic version has the alt-az coordinates, but for a smaller database of objects.

In the Sky Safari Pro screenshot at left, I have selected galaxy NGC 7331, centered it, and the current azimuth (88.5) and altitude (62.4) are shown in the upper left. Make sure you center the object. If you don't, it will not show the correct alt-az coordinates. Then move your scope tube so the pointer on your azimuth circle is set on 88.5 and your digital angle gauge shows 62.4. Look in the eyepiece and, if you have properly leveled and aligned the scope, the object should be in there somewhere. If not, check the wider view in the RACI finderscope if you have one, find the object, and adjust the pointer as needed.

The following are the steps required to find an object with the azimuth circle/angle gauge method. Steps 1-6 are done at the beginning of each observing session. Step 7 is repeated for each object you want to observe.

1. Set the telescope base so that the azimuth circle is roughly aligned with either the Sun or Moon during daylight, or any bright object at night.
2. Level the scope. A cheap bubble level will do fine. I use an app. I made some plywood squares with tread tape on them for rough leveling and use composite shims for fine tuning.
3. Put in a low power eyepiece and find a bright object that's easy to align on without a finderscope. Just sight along the tube at something not too high in the sky. Once centered in the eyepiece, adjust your RACI finderscope, if you have one, to match.
4. Look up the alt-az coordinates of the object in Sky Safari or your preferred app. The altitude should match your digital angle gauge plus or minus the accuracy of the gauge. Make sure your gauge is sitting evenly on the top of the scope tube.
5. Adjust the azimuth pointer to match the azimuth shown in the app. Don't wait too long, as this will be constantly changing.
6. Look in the eyepiece and you should see the object, or at least the star field around or near the object. Identify the exact location within the field by comparing your view with the star chart.
7. To move to another object, look up the new object's coordinates and move the scope until they show on the gauge and circle. You may have to adjust the azimuth pointer slightly for inherent inaccuracies if you are in a different part of the sky, but you will be close.

I added right angle correct image (RACI) finderscopes to my scopes to verify I dialed the coordinates in correctly, help identify dim objects among star patterns, or move around an area to look for other nearby objects. You can get by with just having one RACI finderscope and putting a shoe on each telescope, then moving the finderscope between scopes. I do that with a 6x30 finder for my 4.5 inch and 6 inch scopes. I prefer an 8x50 for my 10 inch, and it can handle the extra weight of the bigger finderscope better.

Get a digital angle gauge

This is the easy part. If you have a telescope with a metal tube, pretty much any digital angle gauge will have a magnetic base that will work well with it. If you don't have a metal tube, you can stick on a metal plate or design some other system to attach the angle gauge. You'll need to cover the display with transparent red tape or something to dim it down to acceptable levels.

I chose a Klein Digital Angle Gauge because it has white numbers on a black background, so minimal light, and all I needed to do was cover it with a tranparent red material. I used the plastic pack that the gauge came in as a holder for the red material, and duct taped in a scrap piece of red acrylic I had leftover from resizing a laptop shield and some craft foam. It slips over the gauge with a friction fit. Just make sure the red material doesn't blur the display making it unreadable. The Wixey is another popular digital angle gauge. You can try to find one without a backlight if you are just going to use a red flashlight to look at it.

Making and installing an azimuth circle

There are many variations on the azimuth circle because telescopes are different and observers are different. Check out the megathread Degree Circles on Cloudy Nights for ideas and pictures. The standard way is to make the azimuth pointer movable, usually using magnets. You can also make the circle movable, but that's usually more complicated. You decide how you want to do it, but here's what I did.

For my 10 inch, I cut a notch in the round bottom of the rocker box and glued a paper azimuth circle to the round ground board beneath that. The azimuth pointer rides on a magnetic strip in the notch so I can adjust it during initial alignment and make subsequent fine adjustments.

For my 4.5 inch, my design of the base did not lend itself to simply gluing on a paper circle and cutting a notch, so I cut a circle out of a 1/8" thick sheet of FPVC, which is a light, semi-flexible vinyl, using a craft knife. I made the cut slowly and wore leather gloves for protection. I had to go over the cut mark multiple times until it cut all the way through. Then I glued a printed paper azimuth circle to the FPVC circle and assembled it below the bearing material disk. I drilled a hole in the center through which the bearing bolt passes. Here's my post on Cloudy Nights about my 4.5 inch project, with additional pictures.

For the 6 inch, I couldn't separate the round bottom of the rocker box from the triangular ground board for fear of messing up the electronics, so I cut the FPVC into a ring shape, glued on the paper azimuth circle, then sliced the ring in two places and attached it to the ground board with some double sided foam tape.

The cuts are next to 55 degrees and 295 degrees so I could attach the ends of the pieces to the "ears" of the ground board that you can see sticking out slightly from below the azimuth circle. I used small pieces of double-sided foam tape. You only need to make two cuts, 120 degrees apart, so you can position the bigger ring piece and then the smaller one to complete the circle.

The azimuth circle added 3/4" to the radius all the way around the base. I had to make a new, larger table for the scope because the circle now blocked the eyepiece holders. This new one is 20" in diameter. The original was 18". I took the opportunity to eliminate the unused 2" holes that I had on the old one and make four 1.25" holes on each side, so no matter where I am sitting, I have lots of places to store eyepieces. I also used 3/4" plywood. White paint makes it easy to see where you're putting stuff and makes it less likely someone will walk into it in the dark. See my post on making a table for a tabletop telescope .

Use the website blocklayer.com to design and print an azimuth circle that fits your telescope. Some people take it to a FedEx or another store that will print it for you. I tried that and they printed it slightly oversized, so I just printed it in several pages on my home printer and fit them together. That introduces a tiny bit of inaccuracy, but you're likely not going to get it perfect anyway. It'll still work fine.

The Blocklayer site has a huge number of templates of all types, and it's fun to browse. But for this project, I used Circle Divider templates. There is a green "Metric Version" indicator at the top, which is actually a button to change it to Metric from the default "Inch Version." Leave it showing Metric.

Due to the popularity of creating azimuth circles for telescopes, Blocklayer has added a template for this specifically: Protractor - Setting Circle. It does essentially the same thing as the Circle Divider template, and you could use that instead. It appears they have removed the option to set the scale counterclockwise, which you would need if you had a movable circle and a fixed pointer.

You have many options, including having the numbers on the inside or outside of the scale, black-on-white or white-on-black, size and length of tick marks, numbering of every 10 or every 5 degrees, etc. Choose what you like, but think about readability from where you are observing and using a red light to see it. Change the "Diameter inches" setting to what will work for your scope, then hit "Calculate" or use the slider. The circle needs to fit on your lower ground board or fabricated circle or ring.

These are the settings I prefer:

• Black print on white background
• Tick lines (default)
• Primary increments 10 degrees (default)
• Number orientation = Radial -90 (so you can read the numbers correctly at the eyepiece)
• Outer marks - note that if you choose Outer marks, the diameter you chose becomes the inner diameter, so you need to adjust the size so the outer diameter is the diameter you need (e.g., your ground board is 22 inches, and so you need a 22 inch outer diameter circle, or a tiny bit smaller). Font size, tick thickness, etc. will affect this, so check the info in the center of the circle on the Blocklayer page and adjust everything with the sliders until you have it the way you want it and your outer diameter is the correct size.

If you like my suggested settings and have the same scope, you can download the azimuth circle PDF that I used for my Sky Watcher Virtuoso GTi 150P here. If you need a 22 inch outer diameter azimuth circle, here is the one I created for my 10-inch Hardin Deep Space Hunter. The Cloudy Nights Degree Circle megathread has a bunch of other files created for different scopes.

Once you have the circle the way you want it in Blocklayer, select "diagrams to PDF" at the top, and in the page that comes up, select the paper size you will be printing on, put in the file name, and hit the "Trim" button. Full printing instructions are at the bottom of the Blocklayer page. Hit the "PDF 1" button in the lower right below the circle (to exclude printing the tape that otherwise would also print out). 

Your own computer's settings will determine how you print it once downloaded, but make sure you are printing at 100% and select "tile large pages" or a similar setting that will print the circle over several pages. If you have it commercially printed, make sure they print at 100%. If it doesn't come out right, just adjust in Blocklayer and try again. I like to print a little smaller than the diameter of the ground board so the edge doesn't peel up.

Once printed, check the fit against your FPVC circle or ring. If it's good, glue it carefully onto the circle or ring using contact cement, making sure you get complete coverage with no bubbles or bare spots. Then spray the paper with several coats of a fixative (I use Aleene's Acrylic Sealer - Matte Finish) outdoors because these often have really bad fumes, especially Aleene's. 

Once dry, mount the circle or ring between the ground board and the lower rocker box. For my 4.5 inch, I drilled a 1/4 inch hole to fit the 1/4-20 center bolt, and the circle sits underneath the azimuth bearing plate. Yours might be different. For the Sky Watcher Virtuoso GTi 150P (6 inch), I had to make two cuts to remove an arc 1/3 of the circumference because I couldn't separate the ground board and rocker box. I then reassembled it into a ring and attached it to the ground board with a few small pieces of double sided foam tape. I tried larger pieces of foam tape, but fitting them under the rocker box board was a mess because they would stick before I could get the pieces in position. Smaller foam tape pieces worked much better and it still holds well.

You'll need to make an azimuth pointer. I made mine from a scrap of thin aluminum flashing material I had from a roof job, but you can pretty much use anything. I attached a tiny rare earth magnet to it using duct tape. I couldn't find any glue that would hold permanently- duct tape to the rescue again! Then I took a piece of magnetic tape and attached that to the rocker box board, so that the pointer will move with the rocker box. The azimuth circle is fixed on the ground board and the pointer rotates with the scope. 

For the Sky Watcher Virtuoso GTi 150P, I switched to using a strip of Velcro instead of magnets, because I kept knocking the pointer when reaching for the azimuth bearing lock knob. You can use anything as long as the pointer can be moved over an arc of about 30 degrees. Any less and it will be harder to rough align the scope when you first set it down and still be able to put the pointer within range. Put the pointer where you'll see it easily from your normal observing position. 

The Sky Watcher Virtuoso GTi 150P with new azimuth circle and larger table. The digital angle gauge sits on the top front of the metal lower half of the tube.

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.

10-19-2024 Update: I wasn't happy with how far I had to scrunch down to look through the finder at or near the zenith, so I added an 8-1/2" extension bar made out of a piece of 1x2 furring strip where the dovetail shoe was and put the dovetail shoe on the end of the new bar, moving the finderscope forward and closer to the eyepiece. Wood screws all around. Shifts the balance slightly, but I just move the scope down the dovetail bar a small amount to compensate.

Here’s how to do it

[Note: See 10-19-204 updates below for an improved version that puts the finder closer to the eyepiece.] 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. [Note: With the updated extension, you'll screw the extension bar in here and screw the dovetail shoe to the forward end of the extension bar.]

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.

10-19-2024 Update: The scope with the new extended mount for the finder. Because it sticks out further when the scope is collapsed, I plan on getting a 1-1/2" knob to replace the bolt holding the bracket to the dovetail bar, making it easy to remove for transportation.

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. [1/9/25 update: I picked up a cheap bluetooth mini game controller and it works great. In the cold, I can even keep my hand in my pocket and control the scope. One problem solved.] 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)