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My very first experience with astronomical telescopes was when I built a 114 Hadley. The process demystified reflector telescopes, and the telescope itself gave really impressive results.
I soon wanted a larger, higher-performance telescope. I had so much fun building the Hadley that I decided to design and 3D-print my own 8" astronomical telescope. I could not just enlarge the Hadley directly, as many parts would not fit on a common 3D printer. In addition, there were some design issues I wanted to improve.
The 203 Leavitt, named for Henrietta Leavitt, is the result. If you're familiar with the 114 Hadley, you'll find that this telescope follows much the same design, but with various changes and improvements (see the Appendix at the end).
Version history
v2, 9/26/23 - Most parts of the telescope saw at least minor changes in this update. The focuser was fully replaced with a version that squeezes the eyepiece with a collet and has a finer thread pitch to allow more focus control. The primary mirror mount was also reworked to be easier to assemble and require no lock nuts.
Should I build a 203 Leavitt?
If you have never used a telescope before, I highly recommend starting with the 114 Hadley. It is easy to build and will be easier to calibrate and use due to its smaller mirrors and slower f-ratio (f/8 for the Hadley vs. f/5 for the Leavitt). It is also substantially cheaper, as the Hadley can use an inexpensive spherical mirror in the neighborhood of $20, while a quality 8" mirror will cost more like $300.
But if, like me, you've gotten a taste for astronomy already and want to build a bigger, more sensitive telescope, then the 203 Leavitt is a good place to start.
Shopping list
To build and use a 203 Leavitt v2, you'll need the following materials. All screws should be round-head machine screws, not countersunk. Links are provided for convenience and clarification only; you can get these materials anywhere, and the hardware may be cheaper at a local hardware store.
Around 2KG of black 3D printing filament, in a rigid material like PLA. I used Overture PLA.
48 #10-24 x 0.5" machine screws (used to bolt together all the main pieces)
9 #10-24 x 2" machine screws (used to collimate primary and secondary mirrors)
3 #10-24 x 0.5" thumb screws (used to hold the eyepiece in the focuser, and lock the focuser). Most of the other 0.5" machine screws can be swapped out for thumb screws if you want, which can be helpful in places (e.g. for more easily adjusting tube sections up and down the rods for balance or focal distance), so maybe get a bigger pack of these than just 3. I'm currently using 11.
3 0.5" x 36" metal rods. There are many options of material, solid vs. hollow rod, zinc plating, etc. Almost any option will work well.
203mm (8") parabolic primary mirror. You can use a longer or shorter focal length mirror by just using longer or shorter metal rods. I used a 1000mm focal length and 3' metal rods.
4 small compression springs, big enough to fit around the #10-24 machine screws, and about 20mm free length. The primary mirror is quite heavy, so you want strong springs.
Silicon glue for attaching the mirrors
At least one 1.25" or 2" eyepiece, with 1.25" being much less expensive. I use a 23mm eyepiece for wider views, a 10mm eyepiece for higher magnification for planets, and a 4mm eyepiece for ill-advised difficult-to-calibrate 250x magnification on planets. You can get the whole set together on Amazon. You can also decide money is no object and get some truly amazing views with something like a 13mm Ethos.
Optionally, a collimation helper of some kind. I use a laser collimator.
Optionally, an 80mm fan to help cool the primary mirror. An 8" mirror is often quite thick and heavy and can take some time to cool to ambient outdoor temperatures. A fan can help this happen faster, and help maintain the primary at the ambient temperature as it changes during observation. I used that fan along with this battery case for 4 AA batteries, and designed this mount for it.
You have two options for mounting the telescope. You can print the tripod-mounting middle section, in which case you need to buy a tripod with a compatible quick-release plate.
Or you can build a simple Dobsonian mount, which will require very basic woodworking skill and the following materials:
One 8' length of 2x4
One 2'x4' panel of smooth, high-quality plywood
About 32 wood screws, about 2" in length, depending on how you end up screwing the pieces together
3 low-friction furniture slider feet to help the two plywood surfaces slide smoothly
3 rubber feet to screw into the bottom of the whole mount to help it sit securely on a variety of surfaces. This can also be printed in TPU, and an STL has been provided. If you print these, you'll also need three 1/2" or 5/8" wood screws to attach them.
2 12" bungee cords for pulling the scope down onto the mount, increasing friction. Depending on how slippery your PLA is, and how well-balanced your telescope is, you may need more or less tension.
All-in, you're probably going to spend around $500, with the bulk of that paying for the mirrors.
3D Printing guidelines
If you don't have a 0.6mm nozzle yet, buy one now. This telescope is made out of a lot of very large parts, and what will take 6 hours with a 0.6mm nozzle would take you over 11 hours with a normal 0.4mm nozzle.
The threaded parts of the focuser need to be printed with 0.2mm layers or smaller in order to turn smoothly. Consider printing these with the normal 0.4mm nozzle, and possibly with even thinner layers for more precise focusing. I printed a set at 0.2mm layer height and it worked fine, but when I reprinted with 0.1mm layer height it became very smooth focusing.
The focuser grub screw panel and tripod-mount tube section (if you'll be using a tripod) both need to be very rigid to perform well. Increase the number of perimeters in your slicer for these parts from the default of 2 to at least 6 or 8.
Everything else can be printed however is convenient, as precision and strength are less important. Most pieces, including all the big pieces, were printed with a 0.6mm nozzle at 0.3mm or even 0.4mm layer height. Two perimeters were enough for all of these parts, though if you're going to print the tube sections with a normal 0.4mm nozzle you may want to use three perimeters for strength.
The cell barely fits on the bed of a Prusa MK3S. You will have to turn off the skirt (0 loops) in Prusaslicer to get it to fit.
All parts in the path of light (which is most parts) should be printed or painted black. A matte black PLA is a good choice. Also, don't overcook your PLA--it will become quite glossy if you print at too high a nozzle temperature.
All the STLs for printed parts are provided on Printables. All the STLs are oriented correctly for printing. Do not use supports.
Assembly part 1: Lower section
Assemble the three lower tube segments by inserting a hex nut into each of the slots shown, then fastening them into place with 1/2" machine screws (9 screws and nuts in total). The diagonal screw holds the adjacent segments together, and the two horizontal screws hold the tube onto the rods.
Do not insert the rods into the vertical holes at this step! It will make the next few steps more difficult.
Insert three nuts into the hexagonal openings underneath the primary mirror cell. Screw three 2" machine screws through the cell and those nuts, screwing them nice and tight so that they extend rigidly out the bottom of the cell.
Slide a spring onto each 2" screw, then pass the screws through the holes in the lower tube segments. Insert hex nuts into each of the three knobs, and screw them onto the ends of the three screws.
At this point you can turn the knobs to pull the cell closer or further from the bottom of the tube in each of those three attachment points. This allows you to make fine adjustments to the direction the primary mirror will point, a process known as collimation.
Attach the primary mirror to the cell using silicon glue. Apply a pea-sized blob of silicon glue on each of the three small raised circular supports, and press the mirror into place. The silicon glue should be about 1mm thick when the mirror is pressed into place.
Assembly part 2, option 1: Middle section for tripod
For the middle section of the telescope, you will assemble either a tripod attachment section or a Dobsonian mount section. If you prefer the Dobsonian mount, skip to Assembly part 2, option 2 below.
As in the lower section, use nine hex nuts and nine 1/2" machine screws to assemble the three segments of the middle tube section.
Also insert two hex nuts and machine screws into the tripod mount attachment. Eventually, use these screws to mount the whole telescope to your tripod's quick release plate.
Attach the lower sight opposite the tripod mount.
Assembly part 2, option 2: Middle section and Dobsonian mount
For the middle section of the telescope, you will assemble either a tripod attachment section or a Dobsonian mount section. If you built the tripod mount, skip this step.
As in the lower section, use nine hex nuts and nine 1/2" machine screws to assemble the three segments of the middle tube section.
Take care to make sure that the mounts for the altitude bearings are on opposite sides of the tube section, not close to each other.
Use a hex nut and 1/2" machine screw to attach the lower sight to the tube, on the side opposite the plain blank tube segment.
Use four hex nuts and four 1/2" machine screws to attach each of the altitude bearings to the sides of the middle tube section.
Also, use one more hex hut and a 2" machine screw in the center of each large bearing. You can use this as an anchor to attach a bungee or large spring to pull the telescope down harder onto the mount, increasing friction so it doesn't tilt as easily.
Cut your 2x4 into the following sections:
Two 20" lengths
Four supports with both sides cut at a 45-degree angle, measuring 11 inches on the long side
Two supports with both sides cut at a 45-degree angle, measuring 7 inches on the long side (the short side will be near-zero)
A single 8' 2x4 should do it, as long as you use the 45-degree cut from each support as the start of the next support.
Build two support towers with those supports as shown, so that they rest flat and relatively stable on a table. Each support should be attached to the tower with two screws.
Cut two circles approximately 2' in diameter from your 2'x4' plywood.
Drill a 1" hole in the exact center of each circle.
Attach the two towers to one of the circles by sending two screws into each support and the towers themselves through the bottom of the plywood.
The distance between the top of the two towers should be approximately 10 1/8". This does not have to be perfectly precise.
Place the two outer altitude bearings on top of the towers. Place the assembled middle section on them to calibrate the distance between them. It can be useful to use a small amount of glue on the bottom of the outer bearings at this step, so they do not move from their correct location on the towers as you remove the tube section.
Remove the tube section from the outer bearings, and use two wood screws to attach each outer bearing to its respective tower. Be sure to drill pilot holes as it is otherwise easy to accidentally split the wood of the tower by drilling into the end of the wood.
At this point you can put a screw most of the way into the outside of each tower, about at the level of the top of the taller supports. You can hook your 12" bungee onto the long machine screw on the sides of the scope and onto those screws in the wood, pulling the telescope down harder onto the mount. This increases friction so that the scope doesn't tilt too easily.
Place the second plywood circle under the first, and secure them by sliding the azimuth bearing into the hole in the center.
If desired, you can attach the bearing to the upper circle with three short screws (be sure not to go all the way through!). Or you can keep both the bottom circle and the bearing loose for assembly whenever you use the telescope. Note that if you permanently attach the bearing, your mount will not sit flat on the ground unless the lower circle is also present.
I attached three PTFE furniture slider feet onto the top surface of the bottom piece of plywood, and three TPU rubber feet on the bottom of the bottom piece of plywood. This keeps the mount secure on the ground and improves its ability to swivel side-to-side.
Assembly part 3: Focuser
Push the focuser ring into its place in the top part of the focuser. This is a tight fit and may require a little force! It should snap into place and then rotate (relatively) freely in place.
Slide the grub and focuser tube into the bottom part of the focuser.
Slide the focuser tube into the focuser ring, and screw the ring down onto the tube until the top and bottom sections of the focuser are flush.
Use two hex nuts and two 1/2" machine screws to connect the top and bottom sections of the focuser.
Insert two hex nuts into the back of the focuser's main body, and one hex nut each into the front and back of the grub screw panel. Attach the panel to the focuser using two 1/2" machine screws, and insert two 1/2" thumb screws into the top of the panel.
The collet will squeeze your eyepiece firmly in place when the collet nut is screwed down tight. To improve grip, apply a small strip of black electrical tape to the inside of each of the six sections of the collet.
Insert the collet, and screw the nut on over it. To insert or remove an eyepiece, loosen the collet nut.
Assembly part 4: Upper section
Assemble the spider and secondary mirror holder as follows.
Put a hex nut into a knob, and thread the knob most of the way onto a 2" machine screw. Put that screw through the center hole in the spider, put a spring around the screw, and screw it into a nylon lock nut in the secondary mirror holder. At this point you can turn the knob to bring the secondary mirror holder closer to or further from the spider.
Insert three hex nuts into the other three slots in the middle of the spider, and thread three more 2" machine screws through them until they are pushing on the secondary mirror holder. While the middle screw controls the distance of the secondary from the spider, these three control the tilt of the secondary, just like the three collimation screws in the lower section. Thumb screws for these three can be convenient, but once your secondary mirror is correctly collimated, you rarely need to adjust it again. 2" thumb screws turned out to be pretty expensive, so I just took three of my normal 2" screws and crushed their heads flat in my table vise, which gave me a good enough thumb screw for this.
Insert three more hex nuts into the mounting points on the edges of the spider.
Use silicone glue to attach the secondary mirror to the secondary mirror holder.
As in the lower and middle sections, join the three tube segments with nine hex nuts and nine 1/2" machine screws.
Attach the upper sight to the left of where the big hole where the focuser will be attached.
Attach the spider assembly to the upper tube section with three 1/2" machine screws.
Insert four hex nuts into the focuser mount slots, then use four 1/2" machine screws to mount the focuser to the upper tube section.
Final assembly
Insert the three metal rods through the bottom, middle, and top sections. For correct focus on a 1000mm focus length mirror, the rods should be roughly flush with the ends of the top and bottom sections. The fit is tight, and it may be necessary to loosen both the horizontal and diagonal screws holding the tube segments together to allow the tube segments to move slightly to allow the rods through. Re-tighten all the screws afterward, and the rods should be held securely in place.
You can slide the middle section up and down to balance weight from the upper and lower sections. You might consider using thumbscrews instead of normal machine screws to hold the middle section to the rods to allow this adjustment more easily. The center of gravity should be in the middle tube section.
Usage
Heck if I know, I'm barely getting started in astronomy. Point it at the sky and look in the little hole.
But fine, if you know even less than me, here's a few lessons I've learned in my first handful of viewing sessions:
Getting collimation right makes as much difference as setting your focus correctly. The bigger and faster (lower f-ratio) the mirror, the smaller the collimation sweet spot where you can get a clear image. Take the time to do this carefully.
Magnification is calculated by the focal length of your primary mirror divided by the focal length of your eyepiece. With a 1000mm primary in this scope, that means looking at a planet with a 10mm eyepiece makes that planet appear about 100x larger than it appears with the naked eye.
There's such a thing as too high of magnification. If you put a 4mm eyepiece and hope to see a 250x-size planet, you're likely to get a blurry mess if you can even aim precisely enough to get the planet in view. Precise collimation and focus can help with this, but it won't really matter if atmospheric and light-pollution conditions aren't pristine.
Inexpensive light filters on your eyepieces can make a big difference in seeing particular features. A moon filter will be helpful as the moon is blindingly bright and washed out on an 8" telescope otherwise.
Targets drift out of sight surprisingly quickly because of the rotation of the Earth. The higher your magnification, the more this is going to be irritating.
Set your telescope on the grass rather than a hard surface if possible. This provides a bit of vibration dampening. Definitely don't put it on a wooden patio or deck if you want to have a stable view.
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