After building the Hadley, I wanted something more. There were a few ways to take better astrophotos: aim properly, collect more light, motorize a mount to follow earth’s rotation, or build a bigger telescope to collect more light. I chose to build a bigger telescope.
The Leavitt is the product of a year of work. This telescope is an 8" diameter f/4.5, with a focal length of 48.5". Its 3-pole design makes for easy adjustment of focal length to accomodate a camera fits into a car and weighs less than 20 pounds.
The mirror is an 8" diameter f/4.5, with a focal length of 89.5". I polished and parabolized it myself from January 2024 to August 2024. Its short focal length means the telescope’s views are less magnified and therefore brighter, perfect for deep sky objects. It has also given me great views of Mars, Jupiter, and Saturn.
The body
For the body, I used the existing Leavitt 3D printed telescope design. It uses three 0.5" aluminum rods and 3D printed parts. Each circle is split into three sections joined by screws to fit onto a standard smaller-than-8" print bed. It took two 1kg filaments of PLA, and since .
I designed a few of my own replacement parts. The original mirror cell (the part that holds and tilts the primary mirror) held the mirror in place with glue on three points, but that glue may slightly deform a mirror by a few nanometers. Since my mirror turned out to be accurate to within 1/20th of a wavelength, instead of glue I designed a mirror cell that encloses the mirror in plastic using three spokes with built-in clips stopping the mirror from falling out.
The mirror mount is an all-new design inspired by the Hill Mount I made for the smaller Hadley telescope. I don’t have access to woodworking tools, so I took a page from the mount I designed for my Hadley and designed a 3D printed truss structure. The telescope’s width is more than the size of my 3D printer’s bed, so I had to design it with a front crossbar.
Compared to the Hadley’s Hill Mount, which is 2.5’ tall, my Leavitt mount is 3’ tall. Because the Leavitt’s mirror has a longer focal length, its telescope tube is longer, so I thought the extra height was needed to stop the tube from hitting the ground when aimed upwards. However, I didn’t account for the extra weight of the mirror, which made the telescope tube bottom-heavy and moved the pivot point closer to the mirror. That meant that the extra height worked against the mount and made it more prone to tipping over. It works, but the design could be made more stable someday.
The mirror
I didn’t buy this telescope’s mirror - instead, I manufactured it myself. Amateur mirror making has a long history, and there are textbooks published a hundred years ago that document processes that still works to this day. This was my first time polishing a mirror, and I’m very proud of the end result: a parabolic surface accurate to within 1/20th of a wavelength of visible light - 25 nanometers or so. I worked on this mirror from January 2024 to August 2024, and first light was in December 2024, just in time to see the Mars conjunction.
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I’ll print out a prototype and see if it holds everything the way I want it to.
Question I still need to answer: how do I stop the axles from fall out
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I don’t know how to design a sketch in one document (for say a stepper motor mount plate) then import it into a different document in a different location (for, say, mounting that stepper in a different place)
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Looks like the belts and pulleys I got fit! Now to design the gearbox and 3D print it so my telescope can move very small amounts accurately
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I found a design by d.revan to motorize a telescope using GT2 timing belts and it’s cool. He uses:
GT2 belts and pulleys instead of gears 608-2RS skateboard bearings to let the shafts spin (smart!) a giant mega printed gear attached to wood for the final gear stage 4:1, 4:1, then 15:1 gear stages …but I tried seeing how much the parts would be on AliExpress, and it was surprisingly hard to find gears with the right 8mm bore and wider than normal 10mm belt width.
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I got a mirror that’s 2.3 inches wide. However, several weeks ago, I printed a mirror holder that was designed to fit a mirror 2.46 inches wide. Sure, I could just use the bigger holder, but the bigger the secondary holder the more light it blocks from reaching your mirror. Is it worth a smaller secondary mirror holder that will block half a square inch less light? Yes, I decided. So I opened up the model and slightly scaled it down.
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Visiting family in another city, and turns out there’s an astronomy store named La Maison De L’Astronomie (The Astronomy House)! I called them up to see if they had some secondary mirrors in stock… And they did! They had so many big telescopes, way more small refractors than I was expecting, a huge cabinet of binoculars, and some absolutely massive tripod mounts.
The bbastro calculator says the most optimal uniform illumination secondary mirror size is 62.
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I was cleaning out my boxes when I discovered @Beasmeeply not only sent me a primary mirror, but also a 46mm secondary mirror! Wow! Thank you!
Secondary mirror sizes are weird; apparently having a secondary mirror too small means the outer part of your view is slightly dimmer. I did lots of research into what kind of secondary mirror to use. This calculator says a 62.5mm will give me the most even illumination across the field, but that’s for super huge eyepieces so a slightly smaller one should be fine.
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WOW! That’s a good mirror!
Previously, @BeasMeeply graciously donated me an 8" mirror. The problem: I don’t know what stage of mirror making I have to do.
So I talked to a local astronomy club. I got to use a spherometer to measure the curve - same curvature all around, accurate to within 0.0002 inches. I put it in a foucalt tester, and after lots of help and fiddling I got some pictures of the result!
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I’m not the first person to build a Hadley 3D printed telescope and then want something bigger. There are two 3D printed 8" telescope designs: the “Bradley” is only available by DMing someone on a discord server, and it’s designed for a printer big enough to fit an 8" circle. I don’t have a printer that big! Thankfully, there’s also the “Leavitt”, a design which splits 8" circles into three pieces so they can fit on a normal Ender-sized printer.
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A while ago I was musing about ways to get better space pics, and @BeasMeeply incredibly generously offered to donate an 8" blank sitting in his closet for 10 years if I paid for shipping! Thank you so much! I’ve got it now and it looks incredibly clear. He also sent a metal 1.25" focuser, which was an extra addition I wasn’t expecting.
It’s like I was standing on the edge of an abyss deciding whether not to jump in, and then someone threw a mirror at my back.
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