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I've finally got around to making my flats box.
I decided to go for a cylinder rather than the normal square as I thought it would maximize the amount of reflected light and limit any 'dead' areas. I could also use the Celestrons dust cap retaining pins to lock the flats box onto the 'scope.
I purchased some of the craft board that has a thin foam sheet sandwiched between two sheets of thick paper/thin card. In order to bend the card into a cylinder, I creased the board every 20 mm by pressing the edge of a steel ruler into the board. It took two of the sheets to make a cylinder big enough to fit my C9.25, with only a couple of cm trimmed off.
I then made a reinforcing ring/defuser holder from two strips of the foam board; this time creasing them at 15mm intervals. I stuck these level to the bottom edge so the joins were 90° to the main cylinder joins. These strips were cut wide enough to ensure that the diffuser cleared the secondary housing.
The cylinder was designed to lock into the C9.25s dust cap retaining pins so next I cut two keyways into the bottom outer side. They looked a little weak so I reinforced them with some Christmas chocolate reindeer plastic packaging!
Although the foamboard is quite shiny, I wasn't happy with all the grooves, so I lined the inside with white A4 paper. The Perspex sheet was cut to shape and hot glued into place onto the ledge.
Next, starting at the top, I notched the edge of the cylinder to run the LED string lights cable through and then started to spiral the LEDs around and down the cylinder.
The top cap/reflector was made from two discs of foamboard. One to go inside the cylinder and one to sit proud of the edge. They were glued together before being hot glued onto the top of the cylinder. The LED light string that I bought has an integrated on/off button as well as both up and down brightness buttons with a 3M sticky pad on the back, so I stuck this to the top cap.
As I had previously made myself a 'scope mounted power distribution box with aircraft sockets for power, I removed the 3 pin UK plug/ac-dc converter and soldered on an aircraft plug to match my 12 volt DC supply socket.
The lightbox illuminated.
[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.
By lux eterna
Pretty often I read about people having issues that may be related to backlash in DEC or RA, and I would like to offer a very simple and effective cure for it. I have done it on my HEQ5 Pro but surely it can be modified for any mount that needs it. With this simple fix, I can live with a rather big backlash (with no risk for binding in freezing temperatures).
For DEC, I always balance carefully (neither front nor back heavy). Then I stretch the coil spring until it has a small impact on the DEC balance (and later in the evening I eventually forget about loosening it when I slew away... so you will need some replacement springs. It took maybe 10+ of such mistakes until I stopped forgetting...). The bracket is only attached with double sided tape (on three sides), but the black maintenance plug (not original) also supports it.
RA is usually OK with just the standard method "East Heavy", but occationally the scope is poing due west or east (counterweights pointing north) and then there is no "East Heavy" impact. That is when I use this:
It´s a little hard to see in the pictures, but I get a momentum in RA (in reverse to tracking direction) when I tighten the string. Now, I happen to have the Rowan belt mod which includes a thick nylon spacer inside the gear cover, and that is a good thing here because it adds to the momentum. I usually hook it up an hour or two before the CW bar points due north. Then when it has well past north I will stop the camera, remove the backlash killer and re-adjust "East Heavy".
EDIT: (Sorry, English is my second language...) Should be a torque, not momentum.
By Craig Shaw
I have searched SGL for a tutorial incase this has been covered so forgive me if it has. I've also searched the web in general and couldn't find a full tutorial to do this, so i have collated a couple of tutorials that make it work.
I have managed to get SkySafari to work with a £32 ish Raspberry Pi3 and the cable that came with my scope with a usb to serial converter - the same things you need for connecting to a PC. It allows me to control the scope using the SkySafari Plus app on my tablet or phone AND it creates a wifi hotspot on the Raspberry Pi so it doesnt have to be on a network to work. This also turns the pi into a natty mini wireless router which is handy if you travel since it gives you a private wireless network when plugged into hotel wired internet ?
I AM NOT RESPONSIBLE FOR ANY DAMAGE THAT MAY OCCUR TO YOUR HARDWARE BY FOLLOWING THIS POST OR ANYTHING LINKED TO THIS POST
It takes about 30 mins to do the tinkering, make sure you use the latest LITE version of raspbian.
Raspberry Pi 3 Portable power to it (preferably) Raspbian Lite Image file Appropriate cables to connect your Telescope to it via USB Computer connected to network Network cable to connect Raspberry Pi for initial setup A GoTo / Push To etc telescope mount compatible with SkySafari Plus / Pro A nice case for the Raspberry Pi
You need to know a little about accessing the Raspberry Pi by SSH.
For windows, use Win32 Disk Imager to burn the latest Raspbian LITE image to a micro sd card. Open the card on the pc (called boot) and make a blank file on it called 'ssh' - no file extension. This enables ssh access automatically.
Stick it in your Pi and plug it into your network router and a power source.
Find its ip address - i log into my router by typing its ip address into a web browser and look at connected devices, there are other methods though.
I use a program called Putty to ssh.
There are many tutorials on how to do the above and it isnt as hard as it first seems.
I used 2 tutorials to do this and i will link to them directly as the original authors explain it better than me. The first one is muuuch longer than the second which is just 3 steps so bare with it.
When the first tutorial suggests a reboot after the upgrade, DO IT! Then ssh back into the Pi and continue.
Don't bother rebooting after tutorial 1 either.
Tutorial 1 - Turn Raspberry Pi into a portable wifi hotspot
See 'CONNECTING' after doing step 2 in the next tutorial to actually connect to the scope as what you have just done changes it a bit.
Tutorial 2 - Make it talk to SkySafari App and the 'Scope
You can now unplug the pi from your router. Plug your USB to serial adapter into the pi, your telescope cable into that and connect it to your scope as you would do with a pc (mine is into the AutoStar hand box) and use it as a stand alone adapter just like the £200 SkyFi adapter!
To connect SkySafari to the pi you simply connect your tablet or phone to the pi's network like you would any other wifi network, i called mine Scope, connect using the security key / password you made up in tutorial 1. Open SkySafari and follow step 3 in the second tutorial but with IP address 192.168.0.10 - the port is still 4000 (unless you changed it)
If you are at home and your cable is long enough to reach your router you can plug the pi into that and use your home internet too - which you cant do with the SkyFi adapter!
I am going to shorten my serial cable to make it a neater package, i can always solder new plus to make an extension if i ever need one.
I am also working on finding out how to make it share usb internet so a 4g dongle can be plugged into it when out and about since when you connect to the pi's wifi in the field you will not have internet on the device connected to it.
Also the Pi could possibly be used for imaging or tracking, someone on here will probably know more on this.