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.

3D Moon flyover

I'm a big 3D fan, especially of stereogram pairs that require no special equipment to see. 

Here is a variety of images featuring different formations on the Moon in 3D. Seeing these from a new perspective adds to our understanding of what we observe in our telescopes. In this case, we are seeing them closer than we ever could from Earth, at differing angles, and in simulated 3D. 

These are stereoscopic pairs using the parallel viewing method. See the instructions for my 3D constellations for details on how to view these. With practice, almost everyone can learn to do it. It's worth the effort!

These images were taken by the Lunar Reconnaissance Orbiter Camera, which has been orbiting the Moon on the LRO since 2009. It has taken some spectacular images of the lunar surface, a few of which are reproduced here in 3D. All images are courtesy NASA/GSFC/Arizona State University. I created the 3D versions using Owl3D and created the location maps with Virtual Moon Atlas. Definitely check out the links to details of the images and browse the other incredible images on the LROC web site. If you have those cardboard anaglyph glasses, they have quite a few images in anaglyph 3D, although the 3D depth tends to be unrealistically exaggerated in some cases.

Many of these features can be observed with small backyard telescopes. The Moon's phase is critical, because features at or near the terminator, the line between night and day, are highlighted with long shadows and can be seen easier. Features near the limb, such as the crater Stevinus, can also be seen better when the Moon's wobble, or libration, presents it a little more favorably towards us. A steady atmosphere and a telescope adjusted to the ambient temperature is also very important. Of course, if a feature is on the far side, we won't be seeing it from Earth. 

Check out this cool NASA simulation to see how much the Moon varies in phase and libration throughout a year. You can also check out how the Moon will look now or at another time for the remainder of this year using NASA's visualization tool.

Unnamed crater between Lowell W and Mare Orientale

This 2.8 mile wide crater sits at the edge of the crater Lowell W and Mare Orientale on the Moon's far side. This was taken when the LRO was at an altitude of 47 miles, facing west. Not visible from Earth. See details about this image.

Mare Orientale on the lunar far side. The arrow just below crater Lowell W points to the unnamed crater in the image above.

Aristarchus central peak

Aristarchus is visible in small telescopes, binoculars, and even with the unaided eye. It is often one of the brightest features visible because it is a young crater, 450 million years old, that hasn't had time for its ejecta material to darken. Here is a closeup crop of the central peak of the crater, taken by LROC from an altitude of 60 miles, facing west. The central peak is about 1,300 feet tall and 9,800 feet wide. The crater is over 2 miles deep. The best time to view Aristarchus is four days after First Quarter or three days after Last Quarter, but try for it around Full Moon and you'll see how bright it appears. See details about this image. 

Aristarchus is 25 miles in diameter. Here's another view. See details about this image.

Location of crater Aristarchus in Oceanus Procellarum. South is up.

Messier crater

About 8.7 miles across, Messier is located in Mare Fecunditatis and may have been formed by a low angle impact, causing it's oblong shape. With an apparent size of nearly 7 arcseconds, Messier and its companion crater, Messier A, as well as the two small rays pointing east from Messier A, can be seen in small telescopes. The best time to view Messier is four days after New Moon or three days after Full Moon. See details about this image.

Location of Messier crater in Mare Fecunditatis. South is up.

Komarov crater floor (detail)

Located on the far side of the Moon, the floor of 53-mile-wide Komarov crater is covered with deep fractures created when magma rose from the mantle more than 2.6 billion years ago. The largest fractures are about 1,600 feet deep and 8,000 feet wide. Not visible from Earth. See details about this image.

Lunar Orbiter image of Mare Moscoviense with Komarov crater in the left foreground.

Mare Tranquillitatis pit

Pits are relatively small features that may have formed due to the collapse above a lava tube. They were first discovered in 2009 and over 200 have now been identified. The sharp edge of the opening of this pit is about 330 feet across, and the depth is estimated to be about the same. Computer modeling suggests the temperature in the shaded part of the pit may be relatively stable at about 63 degrees F, and there may be a more extensive cave or cave network. The pit is too small to be seen in backyard telescopes. See this article for details.

Mare Tranquillitatis pit location. South is up.

Mound in Stevinus crater

A fractured mound inside Stevinus crater. This may have resulted from squeeze-up of molten rock in the impact that formed the crater. The mound is about 2 miles wide. Stevinus can be seen in small telescopes, although our view is at an angle, Stevinus being near the Moon's southwestern limb. The central peak can be spotted. The mound is only about 1.6 arcseconds in diameter and may just barely be detected in some amateur images. The best time to observe Stevinus is three days after New Moon or two days after Full Moon, with a favorable libration. See details about this image.

Location of Stevinus crater. South is up.

Location of the dome within Stevinus crater. North is up.

Wallach crater

Wallach is located in Mare Tranquillitatis. The asteroid or comet that hit the basaltic surface stirred up brighter material from underneath. Wallach is about three miles in diameter. This image was taken from an altitude of about 58 miles. A small telescope with good seeing can pick it out from the mostly flat floor of the mare using higher powers. The best time to observe Wallach is five days after New Moon or four days after Full Moon. See details about this image.

Wallach's location in Mare Tranquillitatis. South is up.

Hell Q crater

One of the many satellite craters (smaller craters near a named crater) named after Hungarian astronomer Maximilian Hell, Hell Q is a very young crater only about 2 miles in diameter. At only 1.8 arcseconds in apparent size, Hell Q requires a 6-inch or larger scope with higher power. The best time to observe it is one day after First Quarter or Last Quarter. See details about this image.

Hell Q location. The crater Tycho is just above  center on the right, near the Terminator. South is up.

Tycho

The 53-mile-wide crater Tycho has a large and prominent ray system. This oblique image was taken from an altitude of about 37 miles. The west wall on the far side in the image is more than 14,000 feet high. Tycho is an easy target in any telescope, best observed one day after First Quarter or Last Quarter. The bright rays are most prominent around Full Moon, however. See details about this image.

The central peak of Tycho. The image is about 3/4 of a mile wide. The boulder on top is about 100 yards wide. See details about this image.

Lichtenberg B

Lichtenberg B is a young three-mile-wide crater located in Oceanus Procellarum. The ejecta darkens over time, so the presence of bright ejecta is an indicator that the crater is relatively young. Lichtenberg B can be spotted with small telescopes. Being very close to the northeastern limb, it is best observed six days after First Quarter or five days after Last Quarter using higher powers. See details about this image.

Lichtenberg B location in Oceanus Procellarum

Earth over Compton Crater

Taken at 83 miles altitude, the Earth appears over the far side crater Compton. See details about this image.

New Binocular Space Walk audio guide - Clusters in Cassiopeia and Perseus

I've added a new Binocular Space Walk audio guide, "Cruising for Clusters in Cassiopeia and Perseus." The guided tour takes you through the northern constellations Cassiopeia and Perseus to find 16 of the brightest open clusters in that part of the sky, as viewed from mid-latitudes in the northern hemisphere. It lasts about half an hour, but provides many opportunities to pause the recording to admire the objects and take breaks. Here's the link to the page, which is also available under Quick Hops on the right. Enjoy!

Binocular Space Walk - Cruising for Clusters in Cassiopeia and Perseus

Eyepiece cheat codes: Observing Jupiter and Saturn

Jupiter and Saturn, and sometimes Mars, are the planets that will yield the most detail to backyard astronomers. Not only are they bright, but they are large enough for even the smallest telescopes to see them as balls with shading and details. And of course, there are Saturn's rings! Mars generally needs to be at a favorable opposition to see surface details well. 

Jupiter has its four Galilean moons and Saturn has between two and seven moons accessible to typical backyard telescopes. The moons of Mars are generally too close to the planet to spot except when Mars is close to opposition and you have a steady atmosphere with good equipment. 

A night with a steady atmosphere—good "seeing"—will allow you to have much better views than a night where the seeing is soft, turbulent, or mushy. This is probably the single most important factor in how sharp the view will be. Try to observe when the planet is highest above the horizon. Viewing through a lot of "soup" at low altitude will also make for disappointing views, even on a night of good seeing. Heat rising from rooftops, asphalt, and concrete also wreaks havoc with seeing.

If you are observing with a Newtonian reflector, the image will be rotated 180 degrees (generally south is up). In a refractor or Cassegrain with a mirror diagonal the view will be mirror reversed (north up, but mirror reversed). See this explanation of directions in the telescope.

Jupiter

A complete novice can expect to see two main cloud bands on Jupiter and its four Galilean moons. With more practice, not only the South and North Equatorial Belts (SEB and NEB), but temperate belts in each hemisphere may also sometimes come into view, as well as darkened polar areas. 

In addition, features such as festoons, barges, and other spots that represent the turbulent swirls and storms in Jupiter's upper atmosphere become visible with practice and good seeing. 

The Great Red Spot is also sometimes visible when it is rotated towards us, although in recent years it has become rather wimpy in its size and color compared to previous decades. Look at some Jupiter images to see the types of features to look for.

Above: The moon Io and its shadow visible against the cloud tops of Jupiter. Image by Steve Hill, CC by 2.0, via Flickr

Below: The four Galilean moons are aligned on one side of Jupiter in this image by Ivana Peranic, CC by 2.0, via Jeremy Keith/Flickr.

Jupiter's Galilean moons—those that Galileo was able to see in his tiny refractor: Ganymede, Callisto, Io, and Europa—are the only moons, out of the currently identified 95 Jovian moons, that are visible to amateur observers, and can even be spotted in binoculars. Because their orbits are well known, predictions as to transits across the face of the planet and the corresponding shadows, disappearances and reappearances behind the planet or its shadow, and even occasional occultations and eclipses of one moon by another are available. You can plan an observing session to add these to the interesting details you can see in your telescope. 

The easiest are the shadow transits, which show up as dark black dots on the face of Jupiter. The moons themselves are more difficult to see when they pass in front of the planet, and much depends on the level of contrast with the cloud deck below them. I have seen them many times in my 4.5-inch reflector, but have been unable to see them just as many times. The best time to see them is when they are right on Jupiter's limb or just off the limb. Then they show up as tiny disks. Compare the size to the apparent disks of the other moons against the dark sky away from the planet and you'll see how much smaller they actually are.

Averted vision is unnecessary for Jupiter and its moons. In fact, you'll see the most by looking directly at any feature. Bore your vision into the feature, almost as if you are looking through it, to get the most detail to register. Relax your eye and just let the detail burn into your retina. Really stare into it!

Sketching the cloud belts and swirls that you see can really help you focus on the details. You don't always have to sketch what you see, but try it a few times and you'll be surprised at the amount of detail that is actually visible. You may not see it all at the same time, the same with deep sky observing, but you will build up a complete picture with fragmented glimpses. This teaches you to place a detail within the greater context and you'll also see how the features slowly traverse the globe of the planet in an (astronomical) westward direction as Jupiter completes a full rotation in less than 10 hours—the fastest rotating planet in the solar system. For more on observing Jupiter, I recommend How to Observe Jupiter Through a Telescope by BBC Sky At Night Magazine.

Saturn

Of all the sights a beginner can see in the telescope, Saturn is probably the most striking. When I show it to people at public outreach events, most people are thrilled and some even question whether what they are seeing is real.

While Saturn doesn't show nearly the same amount of detail as Jupiter, and it's remarkably smaller in the eyepiece, the sheer beauty and uniqueness of the planet will keep you coming back whenever you can. Something about the rings is precious. Really.

Above: Saturn by John Spade, CC by 2.0, via Flickr

The rings change their tilt over the years, and with Saturn now in the evening sky, the rings are nearly edge-on. This makes it difficult to see the major feature in the rings, the Cassini Division. This thin dark lane is sometimes visible on nights of excellent seeing with the rings tilted towards or away from us at a significant angle. Look for it at the outward ends of the rings, where they become more visible because they begin to curve the other direction and the gap is seen at its fullest width. This gap that appears so tiny to us is actually almost 3,000 miles wide! The next ring plane crossing is in March 2025, when the rings, being an average of only about 30 feet thick, become invisible in our telescopes. The Cassini Division may have to wait.

Above: Saturn's varying ring tilt, image by NASA and the Hubble Heritage Team (STScI/AURA), CC by 2.0, via Flickr. Cassini Division label added.

If you look carefully you will usually see a slightly darker band around Saturn and perhaps some subtle shading elsewhere, especially at the poles. Saturn is much smoother than Jupiter, but it does have very infrequent storms visible in our telescopes, such as the great white spot of 2011.

For Saturn's moons, you'll have to use averted vision for all except the largest, Titan, and Iapetus when it is furthest out on the western side of Saturn and its bright icy side is turned toward Earth. Iapetus strays pretty far from Saturn in its wide orbit and can easily be confused with background stars. The inner moons are dimmer, but with good seeing, patience, and a telescope of around 4 inches or more, you should be able to pick out Rhea, Tethys, Dione, and possibly Enceladus. Mimas is quite difficult, Hyperion requires a larger telescope of 10 inches or so, and you won't have a chance at any of the other moons of Saturn, which currently number 146 and counting [Mar. 2025 update: now 274 and counting!].

Jupiter and Saturn observing resources:

Help! I Can't See Detail on the Planets! (excellent article on the pitfalls of observing the planets)

Cloudy Nights Planet Gallery (more recent images at top)

Cloudy Nights Major and Minor Planetary Imaging thread (latest images)

Online interactive observing tool for Jupiter's Moons (Sky & Telescope)

Great Red Spot transit times (Sky & Telescope) (when it crosses the planet's central meridian)

Online interactive observing tool for Saturn's Moons (Sky & Telescope)

Apps:

Moons of Jupiter and Saturn (Android)

JupitersMoons (iOS)

SaturnsMoons (iOS)

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.