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[A few more photos are in the imgur album]
Made this telescope for observing sunspots. The Sun gets projected onto a piece of paper after bouncing from 3 mirrors inside the frame.
It's compact, light, takes only a few seconds to point at the Sun, and sketching sunspots is as easy as circling the spots on a piece of paper.
It can even project the Moon:
The design is inspired by a commerically available telescope, but I’ve done all the designing myself, just for the fun of it.
Sunspotter is full of little details that make it interesting. How do you fix the eyepiece in the exact place where it needs to be? How do you keep the lens in place and perfectly aligned?
Building the telescope was a lot of fun, I’ve learned to use a jigsaw, X-Carve and a 3D printer. The plan is to use it to complete the Astroleague Sunspotter Observing Program, but unfortunately I completed it at the minimum of a Sun cycle, and won’t see any sunspots until next year.
Magnification: 75x Size: 41cm x 41cm x 15cm Weight: 1kg Design: Keplerian Projection size: 75mm Materials needed:
Lens: Ø52mm f=750mm achromatic doublet Mirrors: 1, 2, 3 Eyepiece: Baader 10mm ortho 1.5m² of 10mm plywood Wooden glue 5m of PLA filament 12 nails Compressed air Isopropyl alcohol Tools I used:
Jigsaw with a 30° bevel capacity X-Carve 1000 3D printer A laser pointer Clamp Learned modelling basics in:
LibreCAD Easel TinkerCAD Fusion 360
Part 1: Choosing the lens
The idea of a sunspotter is that the light goes through the lens, travels inside the telescope, bouncing from 3 mirrors, enters an eyepiece and the image gets projected on one of its sides.
The distance the light travels before entering an eyepiece is the focal length and it determines the size of the telescope.
I chose a Ø52mm f=750mm achromatic double. Observing the Sun doesn’t require a large aperture, 50mm is more than enough. I wanted a high magnification and went for the longest focal length I could find, which was 750mm. Achromatic doublet design is what people use in refractors. If it is good enough for a refractor, it’s definitely good enough for my project.
With the focal length chosen I could design the wooden parts. A drawing showed that the frame needed to have sides 30cm long, but I wasn’t sure about the placement of the mirrors and went for 31cm sides, planning to shorten the light path as needed by adjusting mirror positions.
This is the LibreCAD drawing of the layout of parts on a piece of plywood:
Part 2: Building the base
Having a drawing of the base in LibreCAD, I printed the drawing 1:1 scale on multiple A4 sheets of paper and glued them together. I transferred the drawing to a piece of cardboard and cut it out.
Applied this cardboard template to the sheet of plywood, and cut out two parts with a jigsaw.. I’m not an experienced user of jigsaw, and couldn’t manage to cut half-circles accurately enough. Even worse was that the two parts were very different. I didn’t want the frame to randomly tilt left or right when adjusting its altitude, and had to spend a lot of time with sandpaper to make the halves as similar as I could.
Glued the two large parts with three small parts in the middle. Additionally nailed the parts and the base was ready.
Part 3: Frame
The frame is simply a triangle made of three pieces, with short sides cut at a 30° angle. Most jigsaws can cut at 45°, but not at 30°. Had to buy a new jigsaw with a 30° bevel capacity.
Cut out three sides, cut short sides at a 30° angle, but didn’t put them together just yet.
The lens needs to be perfectly aligned with the Sun-facing part of the frame, otherwise the Sun projection isn't circular but elongated.
My solution was to carve a hole with a little step as shown on the image.
The inner hole is Ø46.5mm, the outer hole is Ø50.8mm.
The outer hole is the exact size to let the lens fit, but with a little bit of friction. Had to carve several holes to find the minimal size the lens could fit in.
The step is just large enough to have enough surface for the glue to keep the lens in place, I didn't want to reduce the aperture too much.
I used an X-Carve for carving and Easel for modelling.
With all 3 sides ready, I could assemble the frame. It appeared that my 30° angle cuts were not very precise, but after some sandpapering the sides started fitting together alright. Glued the parts together and left them to dry for a day. To apply some pressure on the joints, I wound several twine loops around the frame really tight, made sure all sides fitted well together and left it to dry like that for a day.
Part 4: Mirrors
When selecting mirrors I was looking for the smallest mirror that fit the cone of light. Small mirrors are a lot easier to place, and they let me better control the length of the light path. I considered using elliptic mirrors, but they were bulky and really hard to place. All mirrors are first surface mirrors, otherwise planning their locations would be a lot more confusing.
This was my original plan of placing the mirrors:
As you can see, all the angles and distances were carefully measured, and I wanted to simply make mirror holders of those exact dimensions. This was clearly a bad idea.
I 3d-printed some parts like this:
And only later I realized that the frame angles are not exactly 60°, and that there are drops of glue along the edges that don’t let me fit the pieces deep enough in the joint between the sides.
I cut angles from all the mirror holders:
After I put the first mirror in place I realized the angles are all wrong, and that I needed to re-do the holder. Separating the mirror from the holder was a huge pain, which resulted in an accident. The mirror fell off the desk and got damaged.
Luckily, only the back side got damaged, the front side was still working:
The final designs of mirror holders looks like this:
The holes in the front surface let me apply pressure on the back of the mirror if I ever want to separate it from the holder. The recesses collect the excess glue to avoid mirror skewing when gluing them.
All other holes are simply to save the filament.
Part 5: Placing mirrors
What I learned is that you can’t plan positions of several pieces with high precision and just hope that it all comes together. I needed a feedback about the precision of mirror positions.
I used a laser pointer to verify mirror positions at each step.
In the picture you can see that the laser is firmly set in a hole in another piece of wood, with layers of isolation tape on the tip of the laser pointer to make it stable. A clamp holds the piece of wood in place, ensuring that the laser ray goes in the same direction as a solar ray would. A crosshair of black thread at the center of the lens ensures the laser goes exactly through the center of the lens.
When placing each mirror, I marked the spot where I expected the laser to end up. While gluing the mirror holder to the frame, I kept the laser as close to that spot as possible. If for some reason, the laser couldn’t hit the expected spot, I did my best with placing the mirror, and recalculated locations of the following mirrors.
I saw the first sunspots after placing all the mirrors and simply holding an eyepiece in hand.
Part 6: Eyepiece holder
I tried eyepieces of different focal length and liked the picture I got with a 10mm eyepiece the most.
An eyepiece needs to be in a very exact spot to produce a sharp image. At this point it was obvious that my frame doesn’t match the model, and that I didn’t even know what exactly was wrong with the frame. I didn’t want to rely on the model and moved forward with trial-and-error.
I printed several parts to hold the eyepiece, with different eyepiece locations:
The part in the photo was a total disaster. It needed quite a lot of filament, at the same didn’t have enough surface area to be glued to the frame, and not enough surface area to hold the eyepiece firmly.
The next iteration was a lot better:
This part has a lot more surface area, and needs less filament to be printed. I intentionally printed the hole for the eyepiece too small, and had to sandpaper it a little bit, to make the eyepiece stay firmly fixed.
Adjusting the focus is done by sliding the eyepiece up and down until the Sun becomes a circle with well defined borders.
Part 7: Dust
All optical parts should be kept clean. Dust on the mirrors and the lens will make the image darker. Dust on the eyepiece will show up as artifacts on the projected image. Unlike sunspots, the artifacts will not move with the Sun. To clean the eyepiece I used compressed air. To clean the mirrors I used isopropyl alcohol.
Part 8: Fire safety
Don’t leave devices with magnifying lenses lying around. Once the Sun happened to be in such a spot that its light went right through the lens, burning through the cap of the eyepiece. Luckily, nobody was hurt and no other damage was done.
Part 9: Future work
Build quality of the base is very poor. The frame tilts sideways when adjusting its altitude despite all my efforts. I’d like to build a new base, but leave all the work to the machines. I already have a model for an X-Carve to make both base parts, compatible with my current frame:
A notch along the edge of the half-circle should eliminate the tilt. The precision of the machining should make the base very stable. Maybe next year, when sunspots become a common daily sight, I’ll get to this project.
Thank you for reading this far!
I hope you enjoyed it.
It's been a long time since I've posted in this forum, anyway I've picked up a Skywatcher 200p F/6 dobsonian as a DIY project whilst I continue to work on a new telescope from scratch, (I've started to grind the mirror).
I'll be making improvements to this dobsonian as a project and learning experience, I've already got a temperature controlled fan which has a probe that can measure both mirror and ambient temperature. I'll be measuring the primary mirror with my in progress Foucault/Ronchi/Bath Tester when that's finished in the next couple of weeks, may even refigure it depending on results.
But I'm most excited about this right now. The blackest Black Paint as an alternative (hopefully better alternative) to flocking!
This stuff is seriously black and flat, I backed it on kickstarter and received 3 bottles along with goodies.
I plan on painting the area opposite the focuser, area around the primary mirror, inside the focuser drawtube, potentially the secondary mirror holder and edge of the secondary also.
It's a shame I don't have any flocking to compare it with but it looks incredible.
This video shows just how impressive it is (moreso than my little tester I've done).
I'll try and get some decent before and after pics.
I wasn't sure where to post this tip....it is probably of most use here....
Many of us with observatories or indoor Mission Control use Windows 10 Pro Remote Desktop to control a scope side computer running camera and scope control software from a second computer indoors. This works superbly at 1080p resolution.
However, I have struggled for a year trying to perfect a wireless solution that works with 4K UHD cameras terminating in a 4K UHD display. Until now, whilst cat 6 cable does work fine, wireless even at 5Ghz 802.11ac has struggled with some lag and poor performance. I have spent a fortune upgrading wireless adapters and range extenders, but this isn't the issue!
Here is a solution;
1. Seperate your dual band network into distinct 5Ghz and 2.4 Ghz channels.
This is easy with (say) a BT Home Hub. If you don't do this, it can be a bit hit or miss whether your 5 Ghz wireless adapters connect to the right channel. You will now see TWO channels, one at 2.4 Ghz with a suffix like <hub name> and another at 5 Ghz named <hub name -5>. Connect your 5Ghz adapters to the latter. If your internal adapters are merely 2.4Ghz, you can disable them via Device Manager and plug in a USB version costing around £5. Note that at 5 Ghz wireless range might drop. If so, a Netgear EX8000 wireless extender is recommended as it employs 'mesh' technology.
2. ONLY if you have a fast network, and powerful CPUs and quality graphics card, try DISABLE 'RemoteFX compression' in RDP.
This allows uncompressed screen data to flow across RDP. I have found this improves performance whether using 802.11ac wireless or cat 6 cable. What RemoteFX compression appears to do is limit effective RDP speeds to under 10Mbps (due to translation times). That is crazy if you have 433 Mbps adapters, and an 802.11ac network (or catv6 cable). Unleash the beast! Send across uncompressed data! The issue is not with speed or bandwidth, it is an artificially imposed limit in RDP.
To do this type 'Edit Group Policy' in the Windows 10 Pro search box (doesn't work in Win 10 Home). You need to drill down through about five levels of Windows Configeration Folders, and Administration Templates and Remote Desktop Services/Host folders to find a utility named <Edit RemoteFX Compression>. In that, your options are <disable> compression or <enable> a compromise mode.
If you don't know how to do this try Googling 'Disabling RemoteFX Compression' to find a lengthy Microsoft tutorial. Or visit https://docs.microsoft.com/en-us/windows-server/administration/performance-tuning/role/remote-desktop/session-hosts .
I deliberately don't here state the quick route sequence to access this deeply embedded network utility command because you are delving deep into developer/administrator territory and do need to understand what you are doing and how to revert to your original RDP settings if your network can't handle these levels of uncompressed screen data. We don't want any novice attempting this on a cheap Compute Stick on an inadequate network!
3. When employing RDP from your computer indoors, select <WAN 10 Mbps> or <LAN 10 Mbps> as appropriate via <Options><Experience>. The default <auto-select my connectivity> often selects too low an option. The irony here is you can select this and still not enjoy faster speeds unless you have edited/disabled RemoteFX compression.
I now have Atik Infinity plus CPWI software running in an end to end 4K UHD system terminating in a 4K UHD monitor. Over 802.11ac wireless it is now rock steady. Over cat 6 cable my system is now turbo powered. If you don't need RemoteFX Compression, don't let it restrict your network performance. It is evidently set to ensure it works on lowest common denominator networks. If you have a fast network/CPU, disable RemoteFX compression and finally release the beast of 4k UHD over RDP.
In the famous words of Bilbao Baggins, I'm going on an adventure!
Almost 2 years ago i got rid of my old shed with the intention of replacing it with a R O R shed,
Well a lot has happened since then, but no R O R shed ? No way i could build one, my DIY skills are rubbish.
My mount and scope plus other bits have sat in the garage ever since, mainly because it's such a pain to drag everything out and set up only to be thwarted by cloud/rain, so i decided that they would stay in the garage until the arrival of R O R shed,
so fast forward 2 years.....
Well! while browsing some astro sites i happened across an advertisement which said something like wooden observatory for sale, 7ft x 7.5ft, buyer to dismantle and remove, so me being in need of one had a look at the pictures he posted, that will do nicely i thought, so i contacted the seller and asked for more info and pictures,
It's not a roof that rolls off onto supports, it turns out 1/2 of the roof rolls over the other 1/2 with a front section of the shed that drops down,
I was happy with what i received from the seller, he couldn't have been more helpful and seems a really nice bloke,
Right then, where are you located mate i asked,
Bovey Tracey he replied,
to be honest, i had never heard of it, so time to consult google maps..
Well it turns out it's only about 270 miles one way from my house in Lancashire ? (so round trip of approx 540 miles)
Time to make a decision, do the positives outweigh the negatives, is it going to be a cost effective solution in getting my R O R shed ?
after doing some calculations and a little more contact with the seller, the answer to the 2 questions above is YES ?
I have hired a box van for this coming Saturday,shangied my brother in law to accompany me and..
I'm going on an adventure to Bovey Tracy to dismantle it and give it a new home in sunny Lancashire,
even though my DIY skills are rubbish i feel i have to give this a go,
All in with the cost of The Obsey (as it is now known until i can think of something better) and with the hire van/fuel and brother in laws dinner
it's going to set me back approximately £570 and a day out, I'm well chuffed with that, the cheapest quote i had to have one built was £1000
I have a couple of pictures of the obsey in it's current location if anyone would like to see them,
Sorry to waffle on so long,
Thanks for reading
I have a steel pier for sale. This was purchased along with a pulsar dome and believe it is an older Pulsar model. The pier sat in a yard, exposed to the elements for a few years before I purchased it so there is some surface rust and flaking paint but will clean up nicely. £250 and buyer will need to collect from Suffolk.