Why pick up a low quality, wobbly telescope from the department store when you can craft your own – just like Galileo, and all the great astronomers from history. For a minor investment, you can build a worthy telescope out of spare parts and high quality kits.
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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest-running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser Cain: Astronomy Cast Episode 327: Telescope Making, Part 1. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today and with me is Dr. Pamela Gay, a professor at Southern Illinois University, Edwardsville and director of CosmoQuest. Hey, Pamela. How are you doing?
Pamela Gay: I’m doing well. How are you doing?
Fraser Cain: Good. We are recording this episode shortly before Christmas so by the time you receive this there will have already been Christmas.
Pamela Gay: As my husband put it this morning, it’s Christmas Eve eve.
Fraser Cain: It is Christmas Eve eve. It is the – what do you call it? The Penultimate after before penultimate?
Pamela Gay: I call it the day that all of the baking occurs.
Fraser Cain: We’re making truffles today. So that’s the plan: chocolate truffles.
Pamela Gay: That is far more exciting.
Fraser Cain: I know. They’re so easy. They’re super easy. So hey, thanks to everybody for joining us over this entire year. We’ve put a lot of effort into keeping the schedule and I hope you’ve noticed that and I hope you enjoy everything we do for the next 17 years of Astronomy Cast. Consider that our Christmas gift to you.
Pamela Gay: I just have to say for those of you in the U.S. who need that final tax deduction because, like me, you already plugged things into Turbo Tax and went, “Oh, blah!”
Fraser Cain: “Too much! How can I write some of this off?”
Pamela Gay: Yeah. You can donate to Astronomy Cast through SIUE. It’s a 501(c)(3) nonprofit and it is tax deductible where the law allows.
Fraser Cain: Nice. Alright. Let’s get rolling.
Female Speaker: This episode of Astronomy Cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember that’s www.8thlight.com. Drop them a note. 8th Light. Software is their craft.
Fraser Cain: So why pick up a low-quality, wobbly telescope from the department store when you can craft your own just like Galileo and all the other great astronomers from history? For a minor investment you can build a worthy telescope out of spare parts and high-quality kits. So this is going to be a two-part episode. Three-part episode, actually. We’re going to do the first part today. We’re going to talk about toys and kits and —
Pamela Gay: Playing with lenses.
Fraser Cain: Yeah. Playing with lenses and building telescopes as an educational experience and just starting to understand how optics work and being able to get into that. Part 2 we’re going to talk about the serious business of amateur telescope making which is a way for you to really craft your own lenses and build the hardware and —
Pamela Gay: Mirrors.
Fraser Cain: Mirrors.
Pamela Gay: Don’t make your own lenses. That hurts.
Fraser Cain: No, no. Some people do it. Mirrors; build your own mirrors and build the hardware and select your mount and really get into the nuts and bolts of what it takes to actually make a telescope. Then, for Part 3 we’re going to talk about building a space telescope, which I think is really exciting.
Pamela Gay: Because some people do that.
Fraser Cain: I know.
Pamela Gay: Which is awesome.
Fraser Cain: There have been a ton of really dramatic changes in the industry and they’ve enabled people to build their own space telescopes so we’re going to get into the – and we’re at the cutting edge of this right now so we’ll do a lot of speculation of what’s possible but yeah, it’s going to be pretty cool. So let’s get started, then. So let’s say a person wants to build a telescope and I think to get to what is the core parts of a telescope that people need to know about?
Pamela Gay: Well, so there’s a lot of different places to get started. What I do with my students is I’ll actually just – this is lame but if I’m trying to explain how telescopes work so that they can get the sense of what they want to build, I’ll go grab a pair of magnifying glasses. You know the type that you use to set things on fire in the summer?
Fraser Cain: I sure do! Oh, wait.
Pamela Gay: You have children; you know how this works.
Fraser Cain: And I had a childhood. Yes.
Pamela Gay: Exactly. So go grab yourself a pair of not identical magnifying glasses. So one little, tiny, wussy, doesn’t magnify things very well. Preferably with a nice, big lens. Then, nice, high-power magnifying glass. You can get these at any big-box store. They sell them for sewers; they sell them for people who have trouble reading. They sell them in the kids’ section. Just grab yourself a pair of cheap magnifying glasses. Then go find yourself either a pair of cardboard boxes or a pair of chunks-o-Styrofoam and stab the magnifying glasses in and you can now start seeing how the lenses work at different distances.
The quick and easy way to understand the way light passes through a telescope is get a light with an incandescent bulb where you can see the filament or fluorescent bulb that has a neat, spirally structure or something to it. Point one magnifying glass at that neat light source and let the light go through the lens and project it onto a piece of paper. Try moving the piece of paper back and forth until you get a nice, crisp image of whatever it is you’re looking at. If there’s two of you, you can actually play the game of, “So if I pulled the lamp further away from the lens, what happens to my image distance?”
You can start to see how the equations for building a telescope work. It’s really neat. If you do this with both lenses, you can see that not all lenses focus at the same distance and this is why I like putting them in two boxes. So you can start out with the lenses side by side looking at a light source and see the differences side by side and move the paper to get it right for both lenses and see the differences.
Fraser Cain: So really the most basic telescope of all is to just get those two magnifying glasses and now you’re recommending put them into a box so that something’s holding them but you could really just hold the two lenses, move them back and forth, and start to see what that does and —
Pamela Gay: Right.
Fraser Cain: – how that changes. It’s going to change the focus; it’s going to change the distance; it’s going to change a bunch of parts of this, right?
Pamela Gay: The neat thing about doing this is this whole idea of using the piece of paper to project the image of the lamp you’re looking at. If you separate the two lenses by the addition of those two distances – so like the distance lens. One focuses at the distance lens two focuses at. Add those two numbers together and separate the lens and then stick your eyeball in and now you have a telescope.
Fraser Cain: Perfect. So now the first time that you look through this handheld telescope, you’re going to see something surprising, right?
Pamela Gay: Yeah. Images don’t necessarily stand up in the way you’d expect them to. You’re going to find that in the process of bending the light through the lens, the image gets flipped upside down and that’s kind of cool.
Fraser Cain: Yeah, and why is that happening?
Pamela Gay: It’s literally a matter of the light rays are getting flipped as they pass through the lens. So if you look at the lens and you think about it for a minute, no matter where you put your eye, you’re going to be able to see that exact, same light bulb. So there is a light ray going from the top of the light bulb to your eye. You move your eyeball left; there’s a light ray moving from the top of the light bulb to your eye. Well, when the light rays go from the light bulb through the lens, the light bulb light ray that passes through the top of the lens is going to get bent down towards the metal.
The light ray that goes through the middle of the lens straight on is going to just keep going nice and neatly straight through the lens. The process of doing this ends up flipping your image upside down, because you’re bending the ones that are further away from the center and the ones through the center get to go straight through.
Fraser Cain: Okay, so let’s make some modifications to this homemade telescope, then. Right now, we’ve bought two identically sized lenses and we’re going to get this flipped version and it’s going to work like a rudimentary telescope but what if we change the sizes of the lenses?
Pamela Gay: Are you changing the diameter or —
Fraser Cain: Yeah. Yeah.
Pamela Gay: – are you changing —
Fraser Cain: I’m changing the diameter of the lenses, right?
Pamela Gay: This is one of those things that tend to confuse people. The diameter of the lens has nothing to do with anything. It changes how much light you’re going to gather so a bigger lens is scooping up more light but it doesn’t change the magnification at all. What changes the magnification is how curved the surface of that lens is. When you look at the surface of each lens, some of them appear completely flat because they are. We call that a normal piece of glass. As you curve that surface more and more, it is going to bend the light more and more and more.
The more you bend the light, that’s going to end up magnifying the image even more. When you read focal lengths on different lenses, for a spherical lens that’s actually the diameter of a circle that has that curvature for the lens.
Fraser Cain: So if I have a —
Pamela Gay: Not diameter. Radius. It’s the radius.
Fraser Cain: Radius. Right, right, right.
Pamela Gay: It’s the radius of curvature.
Fraser Cain: Right, and so the – but the shorter the number – the smaller the number, the tighter that circle is going to be.
Pamela Gay: The shorter the focal length.
Fraser Cain: Right.
Pamela Gay: Because it’s focusing closer in.
Fraser Cain: Now, do I want the – which one do I want in front? Do I want the one that has more tighter radius?
Pamela Gay: You want the tighter radius on nearer your eyeball so let’s say you go to Amazon – and I found out earlier today you can do this – if you go to Amazon, you can buy all sorts of different lenses designed for playing with optics. Designed for science fair projects. If you buy yourself a 200-millimeter lens and 100-millimeter lens, you want that 200 one up near the front and the 100 one up near your eye.
One neat thing you can do is if you buy lenses that have the same diameter, you can take two paper towel tubes and slot one of them and then just roll it ever so slightly so that it fits inside of the other one and you can fix those, if they’re the correct size, lenses to the paper towel tubes. The reason that you want the two of them is as you learn if you try shifting where your lamp is compared to the lens, objects that are closer to you focus at a very different place than objects that are far away.
Fraser Cain: So as we move those lenses back and forth, we’re getting the focal point in a different spot as we bring them – I’m trying to remember which way it goes. If we keep them farther apart, you’re going to get some things in focus; you bring it closer apart, different things will be in focus. So there is no right distance.
Pamela Gay: An object at infinity is going to focus at the focus length of the lens. So, if I have a 4 mm lens and it’s manufactured correctly and my eyeballs like the universe, when I use it to try and focus on something infinitely far away, it’s going to focus 4 mm away from that lens.
Fraser Cain: That is really cool.
Pamela Gay: Now, as things come in from infinity, I get to move my eyeball back.
Fraser Cain: Literally, a telescope is – that is it, right? I mean for a lens-based telescope we use all kinds of other stuff around it but it’s all just helping out these two lenses. Now, what if we add another lens?
Pamela Gay: Well, it depends on what type of telescope you have. So in some cases you have to have another lens to try and correct for different flaws. Lens-based telescopes – and I think we did an entire episode on this ages back – lens-based telescope lenses, by their nature, focus different colors of light at slightly different distances. When you look at the moon through lenses you end up seeing a slightly red edge and a slightly blue edge as it focuses light. It’s more noticeable with stars than with the moon. To correct for that focusing different colors at different distances, we start adding all sorts of different lenses.
There’s other problems where sometimes the center of the lens is in perfect but the outer edges of the lens aren’t just because of how the lens is made or, more to the point, what happens a lot is light that’s coming in from the edge of field of view is slightly out of focus. The center of your field of view is perfectly in focus. Outskirts of your point of view? No. Elongated. All of these different effects are all different types of stigmatisms just like your eye can get stigmatisms. We correct for them in different ways and one of those ways is just to add lens after lens after lens until that sucker has perfect image.
Fraser Cain: Right. If each lens is very expensive to craft and grind and make and then to double or triple or quadruple – you see where the price of these high-end telescopes just goes up and up and up because there’s just more and more of these lenses trying to really clean up the light as it comes in.
Pamela Gay: One of the really awesome examples that allow you to see how all of these different lenses can work together is the Galileoscope. This is a telescope you get to build for yourself. When you order one of these Oceanside Photo and Telescope – otpcorp.com – who do not give us money —
Fraser Cain: Nope.
Pamela Gay: – but we simply like them a lot – they make these telescopes – they don’t make. They resell these telescopes. They’re fairly low cost and they are both a kit for learning optics and a really nifty telescope that you can mount on just an everyday camera tripod. The lens in the front – that big, light-collecting lens – it’s just a single lens but the eye pieces are made of multiple different lenses pocketed together in different ways to correct for all of those different possible stigmatisms and to re-magnify the field in different ways and what’s neat about how they built these telescopes is they come with a couple of different eye pieces.
One of the eye piece configurations make the telescope work just like Galileo’s telescope and you realize Galileo did miraculous things his lens was really terrible. When you look through it —
Fraser Cain: We never use that one.
Pamela Gay: Yeah. When you look through it you can barely see. You have to get your eye in just the right place and it’s horrible. So when you’re done, you have both a version of Galileo’s telescope and then modern designs for lenses that allow you to take this small device and turn it into a power observing tool that allows you to make out the rings on Saturn and craters on the moon and it’s just a nice plastic telescope that literally, if you drop it down the stairs, it might bounce apart but it works kind of great.
Fraser Cain: What does as Galileoscope cost?
Pamela Gay: It depends on where you order it. A lot of times, they’re under 50 bucks.
Fraser Cain: Yeah, and it is definitely the most affordable, high-quality telescope that you can get your hands on. I mean this was designed by an international team of astronomers, who really know their stuff; who focused on, “Let’s make the best possible telescope for the cheapest possible price.” So if you’re looking to get your hands on a telescope and to learn about optics and make a telescope, we can’t recommend the Galileoscope highly enough. We end up with tons of them. We give them away for – at various conventions and stuff because we’re always trying to get that telescope into people’s hands.
Pamela Gay: I think my favorite moment with one of these was several years ago at the Northeast Astronomical Forum, NEAF. Al Nagler of Tele Vue Telescopes, who makes perhaps the best eyepieces that are publicly available. These are eyepieces that cost as much as some telescopes cost and are worth every penny.
Fraser Cain: It’s like your falling into space.
Pamela Gay: He has an eye for optics where he can look through things and really see the difference between different optical characteristics and Rick Fienberg took over a Galileoscope for him to look through and pop one of is Tele Vue eyepieces on. Al had the initial look of, “Yes. I’ll do this. I’m amused.” Then had the look of, “Oh! Oh, wow! Oh, okay.” There’s a quote on the Galileoscope website of Al’s actual words but watching his reaction, it was one of those startled surprise of, “That’s far better than I anticipated.”
Like when a small child brings you cake and it looks okay but you’re not – you haven’t set your expectations too high and you taste it and it’s like grandma’s cake. That was the reaction.
Fraser Cain: Yeah, that’s great. I mean you’re looking at craters on the moon; you’re looking at the rings of Saturn. You’re seeing Jupiter’s moons; you’re seeing the bands across the planet of Jupiter. You’re seeing the Mars – the disc of Mars. Maybe if it’s close and bright you’re able to see the polar caps. You’re seeing the —
Pamela Gay: It’s the seasons, right?
Fraser Cain: Yeah. If you’re seeing the crescent of Venus, you’re seeing some of the brighter deep-sky object and —
Pamela Gay: Globular clusters look awesome through it.
Fraser Cain: Yeah, Andromeda Galaxy. The Orion Nebula. I mean there’s a ton of stuff. So let’s say – but let’s say you don’t want to go the Galileoscope route, although we highly recommend it. What are some other kinds of kits that people can get their hands on?
Pamela Gay: The other place to go look is Edmund Scientific. Their selectin is constantly changing as different manufacturers change what they have but Edmund Scientific is the plat to go for tough, hard-to-kill educational supplies for all sciences. Astronomy, biology. I remember at one point when I was a kid, for reasons that at the time were interesting, my parents ordered me a dead frog to dissect from Edmund Scientific.
Fraser Cain: So thoughtful.
Pamela Gay: So you can – yeah. Yeah, you can get any educational science stuff from there and they always have all the other stuff but really, the Galileoscope is so much better than everything else out there that’s – there’s other kits based out of Japan. A different version of the Galileoscope. It isn’t as rugged. The Galileoscope was actually designed so you can repeatedly take it apart and put it back together. All the others that I’ve encountered are designed – you put them together and you just hope and wish the cardboard doesn’t get bent.
Galileoscope – I’ve seen kids use it to mock sword fight and it survives. Occasionally, you have to put it back together; find where the lenses went to, but it’s survives. That’s the key.
Fraser Cain: Now, we’ve talked about the Galileoscope and we’ve talked about this mode, which is this lens-based version of telescope but there is a whole other class of telescope, which are the Newtonians —
Pamela Gay: Right.
Fraser Cain: – created by our good friend, Isaac Newton. Let’s go back to the basics again, how – and this is tougher – but how can we make a Newtonian Telescope?
Pamela Gay: Cosmetic mirror. So here you actually want to play with it – play off-axis. Go get yourself a cosmetic mirror. One of the ones that completely magnifies. So if you want to count your eyelashes you can. Don’t know why you would but you could.
Fraser Cain: No, but like a shaving mirror. I understand.
Pamela Gay: Yeah. A shaving mirror, cosmetic mirror. Grab one of those and first neat thing you can do with it is when you’re close, you’re right-side up and as you back away there’s this moment where suddenly you become upside down. The point between right-side up and upside down is the focal length for that telescope. So what you want to figure out how to do is how to take that light and bend it so that you don’t have your face in there so that you can actually focus something from a distance.
Fraser Cain: “It’s strange. Everything I look at with my telescope looks like my face upside down.”
Pamela Gay: Exactly, exactly. To go back to our Styrofoam example what you want to do here is put your cosmetic mirror – most of them come on a stand – and then go find yourself a little, tiny, flat mirror. A lot of wallets come with these. You can steal them out of the wallet and glue it onto a pair of shish kebab sticks or —
Fraser Cain: You can jab it into your Styrofoam as well.
Pamela Gay: Jab it into your Styrofoam and now what you want to do – and use the smallest mirror you can find – is take a nice, big object in the distance, focus the light onto first the cosmetic mirror, then, bounce it off of that flat mirror and tilt the flat mirror ever so slightly so you can put a piece of paper off to the side. What’s interesting with this is, like I said, there’s this moment where things flip from right-side up to upside down. This is because the images are not quite the same here and you will need a lens in order to start focusing things.
Fraser Cain: Right. That was my question. With the original telescope with the refractor, you need the two lenses together but in this case you’re going to need the mirror and then another lens and that in-between mirror. So really it’s three parts.
Pamela Gay: Mm-hmm.
Fraser Cain: It could really do with two parts but everything you’re going to see is just your magnified face so go with three parts.
Pamela Gay: Yes.
Fraser Cain: Cosmetic mirror, mirror to balance the light and then a lens to focus it and if you get everything nicely lined up —
Pamela Gay: This is strictly for educational purposes. Cosmetic mirrors do not have good surfaces; they were not designed for astronomy. They were designed for allowing men to shave and women to put on makeup. Different priorities.
Fraser Cain: Yeah. It’s not going to be really, really high quality but you should get that same thing; things far away, whatever that big mirror is pointed at, is going to look bigger.
Pamela Gay: Mm-hmm, and with this one you actually have the ability, instead of focusing it on paper, to look into that mirror and see what happens and stick your eye in there and measure the distance from your eye to the mirror to the mirror to get the focal length. Another cool thing you can do is if, for whatever reason, you have a nice, perfectly round container or at least perfectly round on the sides, fill it with water and you can use that to focus the light onto your eye.
So this is another case of you’re looking through something and you get to see the magnification. You can actually start to combine different round objects filled with water and lenses to build other optical systems.
Fraser Cain: Whoa! So hold on. I can build – take a jug, like a big beaker or whatever —
Pamela Gay: A fish tank.
Fraser Cain: – a fish tank, yeah, but something spherical like something like cylindrical, fill it with water —
Pamela Gay: Three dimension – not cylindrical. Actually spherical.
Fraser Cain: Like a spherical ball. Okay.
Pamela Gay: Yeah.
Fraser Cain: Right, and then set —
Pamela Gay: There’s flasks like this. Chemists have them.
Fraser Cain: Right, okay. Then set those up and those will act like lenses?
Pamela Gay: Yep.
Fraser Cain: I can just put one over here, one over there and look through and see the magnification. Wow. That’s amazing. So now what are – could we do with these setups that isn’t, maybe, a traditional telescope? Could we go into a magnify – build a microscope?
Pamela Gay: Yeah. This is the type of system that you could turn around and you can build microscopes. My favorite random act of science is hard to do but amazingly fun. Is you can buy fluids that have itty, bitty little teeny, tiny particles in them. Fluids that have little latex balls. You can set up microscopes so that you can look at the little latex balls in the microscope.
You can build what are called optical tweezers by shining laser light through one of these lenses and taking the beams of light that were previously parallel in that laser and so you want to pull the laser back to a distance so the light is fairly spread out when it hits the lens. It’ll focus it down to a point and you can actually grab the little, tiny latex balls with radiation pressure.
Fraser Cain: Wow.
Pamela Gay: So it takes powerful green laser. Do not look at the green laser. Use absolute care with green lasers; green lasers are dangerous but you can focus it through a really good lens. The lower the number of millimeters, the better, and grab things.
Fraser Cain: You recommended earlier Amazon.com and that also sounds like a great place. If you’re not – I think if you’re trying to build a telescope that you want to use after you’ve done it and you want to understand the fundamentals and you want to build a telescope that’s tough and rugged and it’s going to work well, Galileoscope. If you want to —
Pamela Gay: Yes.
Fraser Cain: – just build a —
Pamela Gay: Play.
Fraser Cain: – toolkit of crazy optic stuff, Amazon.com has great – they’ve got crazy industrial chemicals and all that kind of stuff but you can get —
Pamela Gay: It’s terrifying what all they have.
Fraser Cain: I know. It’s amazing but – and because there’s so much stuff that they resell and stuff but the gist is go there and just – you can pick up lenses of different focal lengths and different – and a lot of it is very inexpensive. It’s made for other purposes. One last thing: a source of lenses that someone mentioned to me – Dave Dickinson – was photocopiers.
Pamela Gay: Oh, yeah.
Fraser Cain: If you’ve got an old, dead photocopier, if you can get your hands on one, they have lenses inside of them that you can use and you can use those to build telescopes with.
Pamela Gay: One final – since we brought up lasers and CDs – well, you brought up photocopiers and my brain went to DVD player – if you take a old CD like the AOL ones that we used to all get in the mail or some CD that’s scratched so it doesn’t really work anymore, a CD you don’t care about the fate of and a laser, you can reflect the laser off of the CD and create a diffraction pattern on the wall. So you can see all the different spikey separations.
If you do some math and you think really hard – and this is one of those things I need to write up to put on our website – you can actually calculate how much data can be stored on a CD by measuring the separations and the grooves, which you can calculate from the size of the diffraction spikes.
Fraser Cain: Cool. Can you make a telescope out of a CD? I don’t think you can.
Pamela Gay: No. You can make a spectroscope, sort of, kind of-ish.
Fraser Cain: Alright. Well, now I’m going to pull the trigger. It’s time to wrap this episode up. So next week we will continue this conversation but we’re going to get serious. We’re going to build – we’re going to walk you through building a legit telescope that you can actually use for observing and astrophotography and yeah, it’s an amazing hobby.
Pamela Gay: Start with the lenses and the Styrofoam and the toothpicks and —
Fraser Cain: Yeah. You do not want —
Pamela Gay: Just keep going.
Fraser Cain: – you do not save any money building your own telescope.
Pamela Gay: No.
Fraser Cain: That is clear. So alright, well thanks again, Pamela. We’ll talk to you next week.
Pamela Gay: Okay. ‘Bye-bye.
Fraser Cain: Thanks for listening to Astronomy Cast, a nonprofit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at email@example.com. Tweet us @AstronomyCast. Like us on Facebook or Circle us on Google+. We record our show live on Google+ every Monday at 12:00 P.M. Pacific, 3:00 P.M. Eastern or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at cosmoquest.org.
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Duration: 33 minutes