Those that know me realize that I am quite judicious with how I spend my money. My family might even call me "cheap." Nevertheless I am always on the lookout on ways to enhance my hobby and especially when it comes with an attractive price, (read "cheap" here). So you know that I own a large dob. One of the disadvantages with Dob's is that it is rather difficult, and expensive, to equip them with one of those computer pointing devices we call "goto's." Goto's have revolutionized our hobby by allowing relatively inexperienced celestial navigators find the treasures in the heavens. Now I grew up in this hobby by star hopping my way to my targets and I would never recommend anything different for the novice as it forces the newbie to learn the sky. That being said, there is a place for goto's in the hobby. Goto's allow one to increase the speed at which objects are obtained allowing more time spent observing the object and coaxing out the subtle details which is only possible when one spends time observing it.
Now as I said, goto's for large dob's are expensive and you all know my penchant for conserving those green backs. Fortunately, there is an alternative for those, ahem, "cheapskates" like me. Enter the degree circles. Degree circles are a set of graduated circles that are positioned on the azimuth and altitude axis of the telescope. Together with some software, running on either on a laptop or an iPhone, they can allow the observer to point the scope at a set of coordinates for a specific object. The power for pointing the scope still comes from the observer and there is no tracking capability, but it does allow faster acquisition of the target and thus allows for more time at the eyepiece. All this for less than 50 bucks!
A few months ago I decided that I was going to perform this scope modification. The first thing I did was to read up on some experience of others who went before me. Why learn from your own mistakes when you can learn from those around you eh? A great place for this type of information is the Cloudy Nights forum. Here is a huge thread that has a lot of information on installing these degreecircles.
In this thread, I found several PDF files for various diameter azimuth circles. My 10 inch dob has a 22 inch diameter base board, so I needed a 22 inch diameter circle. I found a PDF file for the appropriate size, and took the file on a flash drive to my local Office Max to get it printed out and laminated. The printing was "cheap" at about 4 dollars. The laminating was even cheaper, free in fact, because I had to show the clerk how to reload the stock and set up the machine.
Once home, I cut out the circle and placed it on my base board, making sure any excess was trimmed off. I then needed to cut out the inside of the circle. I fixed the circle onto the baseboard with some all purpose duct tape.
You can see the azimuth circle attached to the base of the scope in the picture to the left. The white circle in the center is the "Lazy Susan" azimuth roller bearings.
Now for the tricky part. I say tricky because when ever I take a jig saw to a precision instrument like a telescope, I get a bit nervous. Because the base that the scope is attached to is of the same diameter as the bottom board, you must remove a portion of the base so you can see the degree circle. So, I used a jigsaw to cut out a 3" by 1" notch. This allows me to see about 15 degrees of the degree circle. I placed this cutout at the front of the scope, directly below the handle. This allows me to see the bearing while still seated at the eyepiece. I painted the newly exposed surface so the particle board would not suffer an ill affects due to moisture.
So, I am almost complete on the azimuth circle. All I need now is an adjustable pointer. Why adjustable? Well, it needs to be adjustable so that you can get it aligned properly. I will talk more about this in a minute. I affixed a magnet to the base board with some double sided tape. I then fashioned a pointer from some scrap wire. I now have a movable pointer on the azimuth axis. Now I also took the opportunity to affix a bubble level to the base board using the double sided tape. This level comes in handy when setting up the scope at an observation site as the scope needs to be perfectly level to maximize the pointing accuracy.
Now onto the altitude degree circle. I could have done something similar and printed out a degree circle for the altitude bearing but there is a simpler method. I went to my local hardware store, Lowe's, and found what they call an "Altitude Meter." This is degree circle with a weighted needle. It gives the angle from the vertical. Now astronomical altitude measurements are given as the angle from the horizontal, but using my grade school geometry, I can simply subtract the altitude bearing from 90 to get what the indicator on the altitude meter should read when I am on the object. The best things about the altitude meter is that it has a magnet which allows it to be placed and removed from the optical tube easily and was only about 20 bucks.
So now it is complete. When I take it out to my observing site, I first use the compass app on my iPhone to get a rough alignment of the bottom baseboard to North, or 0 degrees. I then make sure it is level using the bubble level. If it is off, I shim up the feet until it is level. I then point the scope to a bright star whose alt/az position I know from a real time running software like Stellarium or my beloved SkyTools3. If the scope is level, then the altitude should be dead on. I just need to move my adjustable pointer to the azimuth that the software is calling out for that particular star. And that is it. I can read the alt/az for any object from the Stellarium or SkyTools3 and push my scope to those bearings and presto, there's the object in the wide field lens. Its like shooting fish in a barrel! It is almost like cheat'n.
Clear skies;
rw
Now as I said, goto's for large dob's are expensive and you all know my penchant for conserving those green backs. Fortunately, there is an alternative for those, ahem, "cheapskates" like me. Enter the degree circles. Degree circles are a set of graduated circles that are positioned on the azimuth and altitude axis of the telescope. Together with some software, running on either on a laptop or an iPhone, they can allow the observer to point the scope at a set of coordinates for a specific object. The power for pointing the scope still comes from the observer and there is no tracking capability, but it does allow faster acquisition of the target and thus allows for more time at the eyepiece. All this for less than 50 bucks!
A few months ago I decided that I was going to perform this scope modification. The first thing I did was to read up on some experience of others who went before me. Why learn from your own mistakes when you can learn from those around you eh? A great place for this type of information is the Cloudy Nights forum. Here is a huge thread that has a lot of information on installing these degreecircles.
In this thread, I found several PDF files for various diameter azimuth circles. My 10 inch dob has a 22 inch diameter base board, so I needed a 22 inch diameter circle. I found a PDF file for the appropriate size, and took the file on a flash drive to my local Office Max to get it printed out and laminated. The printing was "cheap" at about 4 dollars. The laminating was even cheaper, free in fact, because I had to show the clerk how to reload the stock and set up the machine.
Once home, I cut out the circle and placed it on my base board, making sure any excess was trimmed off. I then needed to cut out the inside of the circle. I fixed the circle onto the baseboard with some all purpose duct tape.You can see the azimuth circle attached to the base of the scope in the picture to the left. The white circle in the center is the "Lazy Susan" azimuth roller bearings.
Now for the tricky part. I say tricky because when ever I take a jig saw to a precision instrument like a telescope, I get a bit nervous. Because the base that the scope is attached to is of the same diameter as the bottom board, you must remove a portion of the base so you can see the degree circle. So, I used a jigsaw to cut out a 3" by 1" notch. This allows me to see about 15 degrees of the degree circle. I placed this cutout at the front of the scope, directly below the handle. This allows me to see the bearing while still seated at the eyepiece. I painted the newly exposed surface so the particle board would not suffer an ill affects due to moisture.
So, I am almost complete on the azimuth circle. All I need now is an adjustable pointer. Why adjustable? Well, it needs to be adjustable so that you can get it aligned properly. I will talk more about this in a minute. I affixed a magnet to the base board with some double sided tape. I then fashioned a pointer from some scrap wire. I now have a movable pointer on the azimuth axis. Now I also took the opportunity to affix a bubble level to the base board using the double sided tape. This level comes in handy when setting up the scope at an observation site as the scope needs to be perfectly level to maximize the pointing accuracy.
Now onto the altitude degree circle. I could have done something similar and printed out a degree circle for the altitude bearing but there is a simpler method. I went to my local hardware store, Lowe's, and found what they call an "Altitude Meter." This is degree circle with a weighted needle. It gives the angle from the vertical. Now astronomical altitude measurements are given as the angle from the horizontal, but using my grade school geometry, I can simply subtract the altitude bearing from 90 to get what the indicator on the altitude meter should read when I am on the object. The best things about the altitude meter is that it has a magnet which allows it to be placed and removed from the optical tube easily and was only about 20 bucks.
So now it is complete. When I take it out to my observing site, I first use the compass app on my iPhone to get a rough alignment of the bottom baseboard to North, or 0 degrees. I then make sure it is level using the bubble level. If it is off, I shim up the feet until it is level. I then point the scope to a bright star whose alt/az position I know from a real time running software like Stellarium or my beloved SkyTools3. If the scope is level, then the altitude should be dead on. I just need to move my adjustable pointer to the azimuth that the software is calling out for that particular star. And that is it. I can read the alt/az for any object from the Stellarium or SkyTools3 and push my scope to those bearings and presto, there's the object in the wide field lens. Its like shooting fish in a barrel! It is almost like cheat'n.
Clear skies;
rw
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