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orfest

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About orfest

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    Nebula

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    Zurich
  1. [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. Telescope parameters: 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.
  2. I was looking for a new DIY project for myself and found SID detection. This looks interesting and easy except for the preamp part. Is it correct that preamps for VLF are not generally available and have to be DIY? What should be the frequency range of the preamp? I found some preamp designs for wide range, and some designs for a narrow range of 8-9kHz. Wiki says that transmitters in Europe use frequency that is at least 11.9kHz. What frequency range should a sid-targeted preamp have? What are people doing with the 8-9kHz frequency range? Which preamp design would you recommend for someone with a very basic electronics knowledge? Thank you!
  3. I have the WO prism, sorry for the confusion. I asked Williams Optics support about this defect and this is their response: Maybe I should let it go and just buy a dielectric diagonal instead
  4. I took a closer look at the diagonal and turns out it is a prism I unscrewed the back plate, and there is only a prism, fixed firmly. The picture on the right shows what I'm seeing in the eyepiece through the prism. My guess is that the light is not reflected at exactly 90°, which causes the skew. I have no ideas how to proceed. How would you measure the angle between the light rays coming in and out of the prism? Or what else can be done?
  5. I've recently bought a cheap diagonal, but the image seems not collimated. When the star is out of focus, I don't see it as a ring, but as a ring with one side thinner than another. Without the diagonal the image is perfect. I'm using an SCT, and have never had to collimate it. Is it even possible that a diagonal is poorly collimated? Is there a way to fix it? http://agenaastro.com/gso-1-25-90-deg-99-dielectric-mirror-diagonal-compression-ring.html
  6. I decided to buy a smaller lens (50.8mm instead of 60mm) from https://www.thorlabs.de/thorproduct.cfm?partnumber=AC508-750-A and flat secondary elliptical mirrors on http://www.teleskop-express.de/shop/product_info.php/info/p5216_GSO-Fangspiegel---46mm-kleine-Achse---elliptisch.html
  7. Thanks! These mirrors are cheaper than on edmundoptics.com , but I still can't find a lens that is 60mm and f/12.
  8. Hi friends, I'd like to make this sunspotter device for my personal use. It seems that I need to buy the following components: - Achromatic lens, 60mm, focal distance 700mm - Mirror 50mm x 50mm - 2 Mirrors 25mm x 25mm But I can't find any website selling any of those . I've seen lots of parabolic mirrors being sold in sizes >= 6'', I've seen tiny achromatic lenses, or lenses costing a fortune. Any advice on where to get lenses and mirrors is appreciated. I haven't looked for the plywood yet, but getting it should be easy
  9. Thanks. I'll try to buy a longer dovetail plate. If that doesn't work, I'll try to put some weights around the tube as Mav359 suggested.
  10. Hi, I have Canon 600D and a Celestron C6, but when I attach the camera to the scope, there is not enough dovetail length to balance the system. If I try to attach the camera for the eyepiece projection, the balance becomes even worse. What would you recommend to solve this problem?
  11. Thank you all for the replies. I think I understand it now: Polar alignment depends on the position of the mount. Star alignment needs to be re-done if the mount if powered down. Balancing the scope with the DSLR attached and never rebalancing it again sounds good I tried DARV last night, but was only able to align the scope on 1 star, which is South, 0 declination. That did let me have a 60-seconds exposure with less drift than I used to have on a 30-seconds exposure. I could not do DARV adjustment on East or West horizons, because of trees and a hill respectively Isn't it true, that if I adjust the azimuth of my mount using a star on South, 0 declination, then I can use any other star to adjust the altitude of the mount?
  12. That guide looks really helpful, will try it next time.
  13. Hi, I have a Advanced VX 6', which comes with a computerized equatorial mount with a GoTo. I hope you can explain to me, what should I do when I put a DSLR camera (or a binoviewer, or a heavy eyepiece) on my scope and need to rebalance it. Should I turn off the mount, re-balance, turn it on, re-polar align? If so, how can you polar align the mount, with the camera on it instead of an eyepiece? Is computerized alignment good enough for DSO imaging? I usually deploy the telescope in the twilight. I polar align the mount, balance the scope get started looking at some bright objects. The polar alignment is not really good, but with 2 stars and 4 calibration stars the computer works well enough for observing and GoTo is rather precise. Then night comes and I want to try some DSO imaging, and put a camera on my scope. The balance is off. I need to fix it. What should I do? Usually I proceed as follows: - Turn off the mount. - Balance it. - Turn on the mount. - Re-do the polar alignment. This part is a problem, because it's difficult to aim the scope directly at a star when you don't have an eyepiece, but only have a camera with a rectangular screen. I also suspect that the center of the camera screen and the center of the eyepiece do not coincide. These are my questions: 1. How to properly polar align a computerized mount? My recent attempts show star trails after as little as 30 seconds of exposure. 2. Assuming my current polar alignment is good, can I skip the polar alignment after re-balancing the scope? 2a. Is it even possible to re-use the current polar alignment? When I'm turning the mount off, I'm going to move it around with my hands, and I'm sure I will not move the scope to exactly 0 dec and 0 RA before turning it on, but rather to ±0.5 dec and ±0.5 RA. This should not affect the tracking, but it will make GoTo function imprecise.
  14. Hi, Yesterday I was aligning the finderscope and one of the screws fall off and disappeared. It happens to be the "spring-loaded pivot screw". It was the screw from the 6x30 celestron straight finderscope which comes together with the scope. I guess, I can find some nylon thumbscrews for a replacement, but how important is it to have a "spring-loaded" screw?
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