Eyepiece cheat codes: How to use setting circles on an alt-az mount

I remember when I got my first telescope over 30 years ago, a Tasco 11TR 4.5 inch Newtonian reflector on a cheap equatorial mount, I looked at the setting circles and then ignored them, never bothering to polar align the scope and use them. Probably a good idea at the time, because the mount was not very sturdy, and I was able to quickly find things with a straight through finderscope and starhopping, without polar aligning the scope.

Fast forward to today, and manual setting circles are my go-to method for locating objects. 

What are setting circles?

Setting circles can be used on an equatorial or an altitude-azimuth (alt-az) mount to find objects in the sky. As noted, I don't have any experience with using them on an equatorial mount, but the concept is similar, only you use coordinates of declination and right ascension that don't change for an object. In this article, I am not going to get into equatorial or digital setting circles, but rather those that the observer lines up manuallly by eye on an alt-az mount.

Each axis, in this case altitude and azimuth, moves in a two-dimensional plane: altitude up and down in the sky from the horizon to the zenith, and azimuth in a 360 degree circle parallel with the horizon.

As in the diagram at right, it is convenient for us to look at the sky as a celestial dome, with altitude, graduated from 0-90 degrees, and azimuth from 0-360. A setting circle is a circular scale placed on each axis with the mount leveled and aligned so that 0 corresponds to the actual horizon (for altitude) and 0/360 corresponds to true north (for azimuth). 

Once the mount itself is aligned and leveled, you can move the scope to the coordinates of an object, obtained in real time from an app, and your telescope will be pointed at it. 

The accuracy depends on the construction of the mount and setting circles, and the accuracy of your alignment and leveling. You might get the object right in the center of your eyepiece or it might be out of the field of view but within your finder's field of view, and you'll have to starhop or adjust a little to find it.

For an alt-az mount on a tripod, the azimuth circle will be physically located at the point where the upper part of the mount rotates against the fixed base that is attached to the tripod or pier. 

The altitude circle will similarly be mounted at the point where the movable arm that holds the telescope tube rotates against the fixed part that holds the arm to the mount. 

On a Dobsonian, you typically have to create your own azimuth circle, as shown at right, because manufacturers haven't caught on to the usefulness of setting circles and would rather sell you fancy go-to or plate solving systems. See this post on creating your own azimuth circle. Instead of an altitude setting circle, most people use a digital angle gauge, like this one that I use, sitting on the tube.

Typically, a manual alt-az mount that is designed to be attached to a tripod, such as the SV225 that I use, will have setting circles on it from the factory. However, these may be quite small, making them less precise, and depending on the telescope tube you mount on it, may not be easily visible for the observer. In the case of the SV225, I had to take a few pieces apart to loosen the setting circles enough to be able to rotate them to line them up accurately for each observing session. I put my own pointer marks using blue painter's tape where I could more easily see them instead of the light gray, hard to see, markings that came from the factory. Sometimes I think manufacturers put these things on just for looks and marketing, but you can actually use them!

You can also add a vernier scale to smaller setting circles in place of a pointer mark. This allows you to accurately set them in smaller increments. In the case of the SV225, the circles' smallest increment is 5 degrees, but adding the vernier scale allows you to set to single degrees. I was skeptical that it would help, but found it actually does—a little. Plus it looks more scientific and makes me look like I know what I'm doing! (The setting at left is 273 degrees.)

Adjustable for accuracy

The mount must be leveled as accurately as possible and lined up so that the azimuth circle is aligned with the proper compass directions. You can either make the setting circle rotatable to line up with a pointer, or make the pointer movable. The pointer will show you what the current setting is, for example, once aligned, if the pointer on the azimuth circle is at 270, the scope is pointed due west. 

Regardless, you want the pointers to be within easy view from your observing position. A mount with setting circles built in should have the pointers already well-placed, but as noted, the type of scope tube you use on it may require moving the pointer. 

With a rotatable setting circle, you can position your mount close enough that you only have to rotate the setting circle slightly to get it as accurate as possible. With a movable pointer, you also have to place your mount as close to the correct position as possible and then move the pointer slightly to improve accuracy.

Sequence for alignment:

Here are my recommended steps for aligning your setting circles. Details below.

1. Rough align the mount for azimuth

2. Level the mount for altitude

3. Do a fine alignment on azimuth

4. Rinse and repeat

1. Rough align the mount for azimuth

It's better to do the rough azimuth alignment before you level the scope, because if you have to move the mount it may change the level adjustment needed and you'll have to do it over. If your scope tube is heavy, do your alignment and leveling before mounting the tube.

Because altitude and azimuth coordinates of a given object are continuously changing as the Earth rotates, you will need a charting app, such as Sky Safari, that will tell you the coordinates of objects viewed from your specific location and time, updated continuously. Make sure alt-az coordinates are selected in the settings. Your phone does not have to be connected to a network or wifi.

In Sky Safari, go into Settings > Coordinates and select "Horizon." Rather than futzing with degrees/minutes/seconds, I like to have them set as decimals. Go to Settings > Formats, then under "Azimuth, Altitude" select "DDD.DDDDDD, DD.DDDDDD." Now the alt-az coordinates of any object you select and center will show up in the upper left of the screen. You have to center the object or you won't see its correct coordinates. See the screenshot at left. In the example, 59.2 is the azimuth (toward the northeast) and 68.3 is the altitude of the centered item, M51, the Whirlpool Galaxy.

In Stellarium Mobile, you just tap an object, tap the info box at bottom for details and you'll see the alt-az coordinates.

Once it is dark enough, pick a bright object that's easy to find by sighting along the mount or tube by eye, such as the Moon, Jupiter, Saturn, or one of the brightest stars. Look up the azimuth of the object and move the mount so that the azimuth pointer is on the correct number, as close as you can eyeball it when the mount is lined up as if you had the scope on it. It won't be exact, but close enough that you can adjust the circle or pointer for more precise alignment later without moving the mount. Now you can go ahead and level it.

2. Level the mount for altitude

Leveling the mount will take care of the altitude alignment. The idea is to have the pointer at the 0 mark on the altitude setting circle when the telescope is exactly horizontal, and at 90 when it is pointed exactly at the zenith. Any bubble level will get you there. I use a phone app and it's close enough. Just put it on a flat horizonal surface somewhere on the mount. 

Some tripods have a small bubble level built in or you can add one. With a tripod, you can adjust the length of the legs until it reads level. 

Left: The Sky-Watcher Star Adventurer tripod, like many, has a built in bubble level.

With a Dobsonian, place the bubble level somewhere on the base and level it before you place the tube on it. Inside the box works if you can see it well enough. The simplest method is to use a set of shims under the three feet to level it. You can buy plastic or wood shims. I also have 4-inch squares of 1/2 inch plywood for more uneven ground. You can stack them as needed. Just don't forget to pick them up when you pack up for the night. White tape on them will make them more visible on the ground. You can check the level again once the tube is placed on the base, but I've found it doesn't usually change.

Above: Leveling a tabletop Dob table/base using a bubble level app and a piece of plywood. The plastic shims on the table are for finer adjustments. I put a piece of tread tape on the plywood for better grip on the feet.

3. Do a fine alignment on azimuth

Now that you have the mount roughly aligned in azimuth and leveled, you can mount the tube if it's not already mounted and do the fine azimuth alignment. This is where it's important to either have a movable azimuth setting circle or movable pointer.

Below: My DIY tabletop Dob design uses Velcro for a movable pointer. Most use a magnet, but in this application Velcro works better for me so I don't knock it out of place with my hand when I'm fumbling for eyepieces in the dark.

Again, find a bright object and look up its azimuth and altitude. Usually something about 30-60 degrees up will give you a good calibration. It really doesn't matter what direction it is. It's not necessary to use Polaris for an alt-az mount. Move the scope until the circles show the correct azimuth setting and then the altitude setting, without disturbing the azimuth position. Look along the tube to see that it's roughly pointing at the object. Now look in your finderscope. If you were pretty accurate in your rough alignment, you should see the object in your finder. If not, move the scope around until you do.

Put in a low power eyepiece, find and center the object. Next, line up your finderscope so that it matches the eyepiece view, with the object in the center of both. Adjust the finder with the adjustment thumbscrews to match the eyepiece. You should perform this alignment at the beginning of any observing session regarless of whether or not you are using setting circles. 

Next, look at the alt-az coordinates of the object again in your app and compare them to those on your setting circles. They will likely be a little off. Just move your circle or pointer to match the coordinates from your app while keeping the object centered. The higher power the eyepiece you use, the more accurate it will be, but that level of accuracy is usually not necessary. The closer you can get the match between the listed coordinates and those on your circles, the more accurate your subsequent pointings will be.

Your altitude might be slightly off, too, so adjust that as necessary. 

4. Rinse and repeat

Now you can look up the coordinates of any object and dial them in on your mount. Depending on how well you aligned everything, you may see the object immediately in a low power eyepiece. However, don't be surprised if it's off enough that it's not in the field of view, and you can only see the object, or the correct location, in the finderscope. If that's the case, just use your charting app and starhop to the correct location. You'll be close enough that you should be able to find the object every time. 

I find the greatest challenge when I have to starhop to the exact location is when the sky is either too light polluted to see many stars in the finder, or if the star field is difficult to match to the chart. This is often the case with Sky Safari, as I have to have it rotated correctly to match what I am seeing, it's often very cluttered with objects, and the star magnitude settings don't really make the brighter ones stand out enough from the dimmer ones, making the patterns somewhat confusing. Don't worry, have patience, and you'll find your object. You'll get better with practice.

An added benefit, and the reason I personally went with setting circles, is you don't have to crane your neck to look through a straigh-through finder. You can use one with a 90 degree diagonal (right angle correct image, or RACI). Occasionally I'll try to look through the red dot to get an initial fix, but I usually can't even manage that anymore. Getting old ain't for rookies, as my brother likes to say!

Additonal tips:

• Have a red light handy so you can read the setting circles
• Use a low power eyepiece when you are first locating an object, then move to higher power as desired
• It's not uncommon to have to re-calibrate if you find the settings are off a bit, especially in a different part of the sky. Just adjust the circle or pointer to match the coordinates of a centered object.
• If you're having trouble finding a faint object, look up a nearby bright star and see if you perhaps moved the circle or pointer by accident, then re-calibrate on the star and try again. You can also just starhop from that star if it's close enough.
• If you don't like where the pointer is placed on a commercial mount, simply put a little triangular piece of tape or other marker in the location you prefer.
• If you find you don't have setting circles, don't want to make them, or just don't like using them, try the free AstroHopper phone app. I use both, and I find I like setting circles better. But you're not me.

Below: An alternative solution, the AstroHopper app, in use.

Observing with bad vision

I've worn glasses for about forty years, and my vision has been getting progressively worse, as it usually will. It has stabilized in recent years, but now without my glasses, everything is a blur. I started out with hyperopia (farsightedness) which was joined later in life by astigmatism (irregular curvature of the cornea or lens) so, close or far, it's now all blurry. About 15 or 20 years ago I decided to try contact lenses, and now my typical observing session requires I put them in before going out. I don't wear them regularly, only while observing.

(Image by JSB Co. via Unsplash.)

Vision correction

There are nearly as many degrees and kinds of bad vision as there are observers. Most bad vision can be corrected at least to the point where observing is possible, and the telescope focuser takes care of any basic refractive errors in your vision. That's my case. While I have +6.5 and +7.0 corrective lenses that also help correct for astigmatism, the correction is not perfect. Nevertheless, for me progressive lenses correct enough for me to get through life. I don't recommend trying to use progressive lenses at the eyepiece.

Contacts don't do quite as well for me but they work better at the eyepiece. Although I have toric lenses, the astigmatism is still pretty strong, and I've gotten used to the idea that my views of astronomical objects are not going to be ideal—one of the reasons I don't spend a fortune on eyepieces! I have what's called monovision contacts. My left side focuses at about three feet to infinity and my right side focuses around reading distance. It takes some getting used to after wearing glasses, but within half an hour or even less I'm fully functional. 

(Star images rendered from AladinLite.)

Glasses on

Some people just observe with their glasses on. This requires you to have eyepieces with long eye relief, such that you can have your glasses in between your face and the eyepiece lens and still see the whole field of view, or at least most of it. 

Eye relief is the distance in millimeters from the closest your eye can get to the lens to the furthest point you can pull it back and still see the entire apparent field of view (you can see out to the circular edge of the eyepiece field). For eyepieces with very short eye relief, usually in the smaller focal lengths, this may be the same distance, and your eye has to be almost touching the lens. This can force you to strain and your eyelashes will deposit oil on the lens. 

When using glasses, this point may be closer to the eyepiece than you can actually place your eye, and in that case you will never be able to see the full field of view. Eye relief that is too long may require you to move your head around to catch the sweet spot and can be equally frustrating as the view blacks out when you move your head slightly out of position. Eye relief is also dependent upon the shape of your eye socket and your glasses.

I have yet to find an eyepiece with enough eye relief that works with my prescription, and I have progressive lenses anyway, so I don't wear my glasses when looking through the telescope. I can, however, use various binoculars with long eye relief.

Observing without glasses. Notice how close the eye can get to the lens, making longer eye relief unnecessary to be able to see the full apparent field of view of the eyepiece, which in this case is 82 degrees, nice and wide. Contact lenses require no additional eye relief.

Observing with glasses on. Compare to previous image, noting the much greater distance from the top surface of the eyepiece to the observer's eye. Long eye relief when wearing glasses is critical to being able to see most or all of the eyepiece field of view. This Astro-Tech UWA 10mm eyepiece has only 10mm of eye relief. Not long enough for eyeglass wearers, who need a minimum of about 17-20 mm.

(Images by Astronomerica.)

According to Don Pensack's 2025 Eyepiece Buyer's Guide, eyepieces currently available range in eye relief from a mere 1 to 3 mm for the Harry Siebert Optics Planesphere series to a whopping 46 mm for the Masuyama 60mm 2-inch eyepiece. The caveat on any eye relief figure is that the numbers often only count the measurement from the glass surface not including additional inset or eyecup. So if anything, the effective eye relief may be shorter than the advertised eye relief. This thread from Cloudy Nights discusses some of the better eyepieces for eyeglass wearers. Scroll to post 14 to bypass some rather less useful posts.

Glasses on and off

Another way to cope is to use your glasses when reading a chart or looking up at the sky and then taking them off each time you put your eye up to the eyepiece. This may work especially if you have a relatively mild prescription and maybe only use glasses for reading. For us hardcore Magoos (link provided for younger folks who have no idea), this is fraught with danger. 

(Superman image by DC Comics)

Let me relate my experience in that regard. Before I switched to contacts, I thought I would just swap my glasses on and off when observing. While annoying, this did work to some extent. Until one night, when I placed my glasses atop the roof of my car. They slid off with the heavy dew, and here I was with no way to search for them. Oh, I had a red light, but everything was blurry. I was afraid to move, but I took one step in the direction I thought would be away from the glasses and, you guessed it, heard and felt a sickening crunch underfoot. I managed to drive home that night using an older pair of glasses I had kept as a backup, but that was it for me, and I got contacts shortly thereafter. 

If it works for you, go for it, but be careful. Sometimes I still do use this technique (with my backup glasses!) when I'm just out for a quick look in the backyard or I'm taking a quick look in my solar scope. I recommend velcroing a soft case to your scope or table so you can slip the glasses in there, rather than trusting to a pocket that could contain who knows what that could scratch your lenses or just laying them on a table. I've tried keeping them on eyeglass retainers around my neck but the constant bumping and scraping as I leaned over the telescope was annoying and made me worry about scratches.

No glasses

You might be lucky enough to still be able to read or look at the sky without your glasses and still see reasonably well. In that case, just put your glasses away and use your uncorrected eyes. I did this until the stars just started looking like fuzzy blobs and I was straining to read charts with a magnifier in the dim red light of my flashlight. A man's got to know his limitations, and I had reached mine.

Contact lenses

For me, contacts are really the best solution. With my monovision lenses I can read reasonably well up close, I can drive, I can see the stars reasonably well when I look up, I can see pretty well with any eyepiece, and I've gotten used to using one eye for each. Another benefit is at public star parties, where I can focus an object in the telescope and know that people with reasonably good vision will get a decent look. But a tweak of the focuser will work for most people with uncorrected vision issues, other than astigmatism. I usually encourage people to take off their glasses to observe and just refocus, as long as they don't have bad astigmatism.

There are a few downsides, though. Especially if you don't wear them often, contacts can be itchy, scratchy, and blur out sometimes, especially as your eyes get tired. I sometimes struggle to get them to stay in at first, although other times they just slide right onto my eyeballs and stick. I've had them get stuck under my eyelid when I rubbed my tired eye, and I've even put two in at once, thinking the first one didn't stick and had dropped on the floor. 

Or maybe you just don't like touching your eyeball? Ewwww! (Image by Moist.acuvuehk via Wikimedia, public domain)

I always take a second pair of contacts with me in case I get a tear in one, it just feels crappy, or I somehow lose one out of my eye. Also bring eyedrops to rewet them if they get too annoying. The lens solution bottle won't help unless you want half the bottle all over your neck and down your shirt. Trust me on that one.

Televue DIOPTRX

Televue makes a device they call DIOPTRX that can help with mild astigatism. It looks like a filter with a fold-down eyecup attached that you can thread onto a variety of Televue eyepieces. I've read some accounts that all say it works well. If your astigmatism is relatively mild, but bad enough that correction would make it worth the cost, and you have Televue eyepieces, you might want to check it out.

Can I take pictures through my telescope with my phone?

The short answer: Yes, but prepare to be underwhelmed. My question to you then would be: Why? If the answer to that is you just want something to text or post to show what you were looking at, go for it, but you're really not going to impress anyone. I have people at public events always wanting to take a picture of the Moon through the scope, and I usually oblige them by taking the picture for them, but it slows the line down and won't impress anyone but total non-astronomy folks (maybe). Still, I get it. People want something besides a memory to take home. Frankly, I'm happy with the memories.

Confession: Against all logic, I sometimes try to take pictures through my telescopes with a cell phone at the eyepiece, knowing it is probably a waste of time. The only decent pictures I've ever gotten were of the Moon, which are still far below almost any image I can find on the internet and the detail I can see visually, and some pretty cool images of Spica and Arcturus with an apodizing mask on my 10-inch. Otherwise, the images suck. Granted, I am using a Pixel 6a, which isn't exactly cutting edge now, so if you have a newer phone, or the latest and greatest (for now) iPhone, then you might have better luck. 

Anyway, here is a gallery of images I took through my 10-inch and 6-inch Dobsonians with the Pixel 6a, as a baseline for what you might expect to get, depending on your phone's camera. I will say it is difficult to get the phone's camera lens lined up with the eyepiece while still being able to snap an image before the object drifts out of view. Although I have no experience with eyepiece phone adapters, the general consensus appears to be that they are fiddly and mostly a waste of time and money. If you do get one, the Celestron NexYZ is often recommended. The images I've seen from them, however, are no better than my handheld images. Phones seem to be much better at getting non-optically magnified images like the Milky Way, or a lunar eclipse over some scenery using their night vision mode, or whatever they call it. Bright comets can be kind of nice.

Left: The Moon rising over the hills. This was so cool that I wanted to take a picture to put in my log for that unique sight, just to remember it better. To me, this is the best kind of use case for taking an image through the eyepiece. 10-inch dob.

Left: The gibbous Moon, zoomed in and cropped to show the level of detail, which is nowhere near what I could see visually. 6-inch tabletop dob.

Left: Spica with the apodizing mask. Pretty psychedelic, but rather pointless. Well, there actually are a lot of points. 10-inch dob. Apodizing masks are used on larger telescopes to negate some of the effects of poor seeing for splitting double stars and seeing more planetary detail. I didn't notice any improvement on my scope, as expected, although the kaleidoscope effect is interesting.

Left: Arcturus with the apodizing mask. Far out, man! 10-inch dob.

Left: Comet C/2023 A3 (Tsuchinshan-ATLAS) through a 6x30 finder. The shot through the eyepiece was too awful even to post here as a bad example.

Left: The same comet using the phone's "night vision" capability, without magnification. Especially with distinctive scenery, this can bring back the memory of the night much better than an eyepiece shot can.

So there you have it. Casual photos? Maybe. Anything more, get a SeeStar or go down the imaging rabbit hole and be prepared to spend some money and a lot of time learning processing. If you want to do planets and the Moon, a basic planetary camera might work for you, but you have to seriously ask yourself why you are wanting to do imaging. It's not for everyone but some people just love it, and it's more forgiving of light pollution.

Astro imaging is indeed a different hobby entirely from visual observing. I remember photographing Comet Hyakutake on a homemade barn door mount with a poorly functioning stepper motor and a film SLR camera. I don't even know where the picture is now, but it was so much less inspiring than the actual view of seeing the comet from that dark sky, stretching overhead like a flashlight beam. 

After that, I decided not to waste good observing opportunities trying to capture something mediocre to take home with me, unless I spend less than a couple minutes doing so out of the apparently primal urge for a tangible keepsake of everything to post on social media.

For me, give me visual every time. I'll find the pretty pictures on the internet—and I do, for placing in my log or notes to go along with my visual descriptions, or just to see what an object can look like to an imaging chip with a lot of computer manipulation.

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.