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I wanted a telescope I could take on a plane but that would have a usable aperture and wouldn't be too expensive. The resulting scope weighs about 16.5 lbs, with a mirror box that fits in a backpack and that has about half of the weight, and with all the other pieces fitting in luggage, along with clothes and whatever else I am packing.
The scope looks funny. It has a square box on semicircular rockers on the bottom, then a single wooden strut leading to a focuser board out of which there sticks out a stalk for the secondary mriror, and a rounded coathanger with a light-shield. The original design used two struts, but one is enough at this size. Telescopes don't really need tubes. Tubes are just there for holding the optical elements in place and keeping out stray light, and both tasks can be accomplished in other ways.
After disassemly, no piece is more than 16.5" long. The second photo shows all the parts reading for packing up. I originally planned for the telescope to assemble on location with no tools, but ended up relaxing that to allow for one Philips screwdriver. Using Philips screws in a few places reduced weight over the big wingnuts I would otherwise have used.
The telescope doesn't look like much, but I've had good views of the Whirlpool Galaxy, the Dumbell Nebula, the North American Nebula, the Ring Nebula and various other deep-space objects. It works on planets, too, though it's best for low-magnification deep-space viewing.
I originally planned to use a 6" F/5 mirror, but I got a very cheap 8" F/4 mirror with a crack near one edge. Turns out the stresses induced by the crack only seriously distorted the mirror in one area, and so I blacked that out. That explains the dark semi-circle near one side of the mirror. There are gory details of how I tested the mirror here.
At the time, my woodworking skills were very limited. The power tools I used were:
The optics were:
And if you don't have any telescope yet, you'll need eyepieces. I recommend to start out with a 30/32mm Plossl and a 10mm Plossl.
I also suggest that you read all the steps before doing anything. I am not giving many dimensions as they'll depend on your mirror. I will assume you know how a Newtonian telescope works.
Update: I found my design drawings and after editing them slightly for clarity and to fit with the final version, I posted a couple of them. If you want the SVG files that the images are made from, let me know, but since your dimensions are going to be different from mine, you're better off making your own drawings.
The scope looks funny. It has a square box on semicircular rockers on the bottom, then a single wooden strut leading to a focuser board out of which there sticks out a stalk for the secondary mriror, and a rounded coathanger with a light-shield. The original design used two struts, but one is enough at this size. Telescopes don't really need tubes. Tubes are just there for holding the optical elements in place and keeping out stray light, and both tasks can be accomplished in other ways.
After disassemly, no piece is more than 16.5" long. The second photo shows all the parts reading for packing up. I originally planned for the telescope to assemble on location with no tools, but ended up relaxing that to allow for one Philips screwdriver. Using Philips screws in a few places reduced weight over the big wingnuts I would otherwise have used.
The telescope doesn't look like much, but I've had good views of the Whirlpool Galaxy, the Dumbell Nebula, the North American Nebula, the Ring Nebula and various other deep-space objects. It works on planets, too, though it's best for low-magnification deep-space viewing.
I originally planned to use a 6" F/5 mirror, but I got a very cheap 8" F/4 mirror with a crack near one edge. Turns out the stresses induced by the crack only seriously distorted the mirror in one area, and so I blacked that out. That explains the dark semi-circle near one side of the mirror. There are gory details of how I tested the mirror here.
At the time, my woodworking skills were very limited. The power tools I used were:
- cheap Harbor-Freight jigsaw
- power drill, with a set of hole-saws and a 1.25" spade bit
- friend's table saw (I could have done the cuts with the jigsaw and a good blade instead, like a Bosch Progressor U234X)
- friend's mini-router for one elongated hole, which I could also have done with drill and rattail file (and I could have just had a round hole with better measurement).
The optics were:
- 8" F/4 chipped mirror, bought for $39 on CloudyNights
- 1.83" secondary mirror, bought for $9 on CloudyNights (one end was a bit turned, so I blacked it out)
- Mars's Eye red dot finder (you can also use a Daisy red dot finder from Walmart or Academy, especially with some modifications)
- scrap wood and particle board
- one 14-16" wooden/particleboard/plywood circle, about 1/2"-3/4" thick (see more in step 4 for sources)
- JB Weld
- Titebond II
- silicone glue (the older, smelly kind; the newer non-smelly is supposed to be not as good)
- 1.25" PVC conduit
- 1/4-20 carriage bolts, fender washers and a few nuts
- miscellaneous machine screws and nuts
- 1/16" bondable PTFE (amazon's Industrial and Scientific store)
- 1/4" threaded rod and 3/16" square rod (many ways of doing this)
- one thumbscrew
- some woodscrews
- seven 1/4-20 three-lobe female thru-hole knobs (amazon's Industrial and Scientific store)
- one vinyl record (about a dollar on ebay)
- acrylic flat black paint
- one coat hanger
- some foam board
- four wire ties
- duct tape
- one binder hole reinforcer sticker
- two long extension springs
- three strong compression springs (I used mower engine valve springs).
And if you don't have any telescope yet, you'll need eyepieces. I recommend to start out with a 30/32mm Plossl and a 10mm Plossl.
I also suggest that you read all the steps before doing anything. I am not giving many dimensions as they'll depend on your mirror. I will assume you know how a Newtonian telescope works.
Update: I found my design drawings and after editing them slightly for clarity and to fit with the final version, I posted a couple of them. If you want the SVG files that the images are made from, let me know, but since your dimensions are going to be different from mine, you're better off making your own drawings.
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Signing UpStep 1Measuring mirror focal length
A crucial step that determines the sizes of many parts is to measure the mirror's focal length (don't trust labeling). There is more than one way to do it. My favorite is to take the mirror outside, put it on a soft chair, and point its optical axis at the moon (a bright star, e.g., Sirius or Vega, should do). The optical axis runs through the center of the mirror, perpendicular to the mirror. Then hold a small piece of wax paper on the optical axis, at around that distance from the mirror surface that your mirror seller told you was the focal length. Adjusting the mirror and the wax paper a bit, you should see the moon on the wax paper, reflected from the mirror. (In a sense, you already have a telescope at this step. If you had a camera sensor in place of the wax paper, you could take a picture of the moon.) Move the wax paper along the optical axis until the moon is as sharp as it can be. The distance from the wax paper to the mirror is the focal length.
You will want to design your telescope so that the distance along the light path--remember that in a Newtonian telescope the light path bends at right angles at the secondary mirror--from the primary mirror to the end of the focuser tube with the focuser tube fully racked into the scope is about 1/4" less than the focal length. You can achieve this by adjusting the length of the strut, the placement of the primary mirror and the distance from the secondary to the focuser. Basically, the crucial thing is that your eyepiece's focal plane should go where the wax paper was (taking into account bending of the light path by the secondary).
The design in this instructable is good for short focal length. My mirror's focal length is 800mm. For significantly longer focal length, you'd want more struts than one.
You will want to design your telescope so that the distance along the light path--remember that in a Newtonian telescope the light path bends at right angles at the secondary mirror--from the primary mirror to the end of the focuser tube with the focuser tube fully racked into the scope is about 1/4" less than the focal length. You can achieve this by adjusting the length of the strut, the placement of the primary mirror and the distance from the secondary to the focuser. Basically, the crucial thing is that your eyepiece's focal plane should go where the wax paper was (taking into account bending of the light path by the secondary).
The design in this instructable is good for short focal length. My mirror's focal length is 800mm. For significantly longer focal length, you'd want more struts than one.
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As far as I can tell, they've got a solid reputation in telescope making circles.
Your telescope design is pretty awesome, I've been considering ways to reconstitute my 10" reflector to make it more portable . . . I'm thinking I may try to build this: http://www.sff.net/people/j.oltion/trackball.htm It's definitely not airline portable, but it would be very nice for quick setup and break down.
The trackball is pretty neat, but beyond my skills. Also, my own star hopping relies on it being easy to tell the difference between azimuth and altitude motion. For instance, one thing I like to do is to find a star with the same azimuth (or altitude) as the object I am looking for--I use a Palm TX PDA--and then move in altitude (or azimuth) to it.
without the tube to filter surrounding light do you have any problems with light pollution?
since you ony have the singe pole supporting the eyepiece do you have any problems with wind?
what was your total cost for this?
2. The strut is pretty solid--it's not a problem. The light-shield is a bit of a problem with wind. The last star party I had the scope at it was too windy to keep the light-shield on, but it worked fine without it. I think a bit of velcro on the coathanger and on the focuser would have helped to keep it in place. If you're still worried about the strut, you can switch the poplar for oak.
3. Where there is a bit of shift is with the secondary mirror , which still has a tiny bit of flex that shifts collimation a bit as the scope goes up and down. At least I think that's where the problem is.
4. Cost estimate? I didn't keep track, as I used a lot of scrap that I had lying around. The optics were $48, shipped. Other supplies. I remember an expensive trip to the hardware store to get a lot of carriage bolts, screws and nuts. I think that was probably $30. $3 for the PVC tubing. About $13 for glues. $15 for bondable PTFE on amazon--it was enough for two other telescopes, a binocular mount, fixes for wheels of a stroller, etc. $2.50 for the strut. $1 for the record. $5 for the mower repair guy to pull springs out of dead motor. About $10 for thumbscrew and knobs (one could use cheap wingnuts, too). About $10 for the finder. About $4 for the extension springs. About $3 for the metal rods. About $3 for sandpaper. That totals about $150. I also spent about $40 on tools at Harbor Freight for this project, but which I've used for many other projects: jigsaw, hole saws, work gloves, maybe some other stuff.
If I didn't have all the scrap oak at home, I'd have to buy a 5'x5' sheet of 1/2" Russian birch plywood. That stuff is really nice and really cheap around here at McCoy's, namely $27 per sheet, but it may be twice as expensive or more in your area. I'd probably also have to spend $10-20 on some kind of wooden circles (e.g., cutting board at Ikea).
You don't necessarily save money by building over buying a cheap (but often surprisingly high quality) Chinese-made scope, but you can get something that you can't buy (in my case, something I can take on a plane).