How to make a Newtonian Telescope part 2
In this part we make the actual telescope. This is the tube assembly
I do have a video showing this whole process. You can watch that at the bottom of this page. And here is a picture of the completed tube assembly. This gives you an idea of what it looks like.
I walk you through the whole process of making this telescope. And I will give you the parts and lots of suggestions on different parts you can use and various other stuff that will be of help to you.
Of course you can buy a telescope. And I have lots of advice and help with that on this website but I really enjoy the whole process of telescope making and you might enjoy it too. There is something very satisfying about making your own telescope then getting to use it. And it really isn’t very difficult.
This picture shows me looking through the completed tube assembly. this gives you an idea of the size of this telescope.
The picture above shows us what parts are involved in making the telescope.
- The cardboard tube. Pretty self explanatory and it doesn’t have to be cardboard. it can be wood, fiberglass or any number of other products. For a small telescope like this a cardboard tube is quite good. I have some helpful links on getting a tube at the bottom of this page.
- The eyepice and focuser assembly – This is a little mount that holds the eyepiece. It has a knob on it so you can adjust the focus by moving the eyepiece in and out. (This exact focuser is a 1.25 inch and it is available on telescopes.com right here: 1.25 inch Orion Focuser
- The Right angle secondary mirror assembly. This holds the secondary mirror and bounces all the light out of the side of the tube and into the eyepiece.
- The mirror mount – This holds the primary mirror in place and it is adjustable so you can align up the mirror correctly. I will show you more of this and how to make this. Here is a link to where I bought this primary mirror and secondary mirror pair: Newport Glass
The Cardboard Tube
By doing the test setup in part 1 of this tutorial we now know about how long our telescope tube should be . But how wide should it be? There is a little bit of flexibility in this but typically we want it around 1-2 inches larger than the diameter of the mirror. My mirror is 4.25 inches in diameter and the tube is 6 inches on the inside diameter. So, we have about 5/8 inch all the way around the mirror. this is pretty good. The picture here shows the mirror mounted in the bottom of the tube. You can see the space all around the mirror.
Let’s take a look at the diameter of the telescope tube and why it is a little bit important.
This drawing here shows the same exact mirror in two different tubes. The blue lines are the light path that bounce off the mirror. This light path bounces off our secondary and is sent out the side of the tube.
In the top illustration we see that in the larger tube we have to bounce the light much further to get out the side of the tube. And this means that we need a bigger diagonal mirror. This is the red thing.
Well, with a bigger diagonal mirror we are blocking more light from getting to the primary. And that reduces the effectiveness of our telescope! So…. keep the size of the tube close to the size of the mirror, just a little bit bigger.
And, if you buy your primary mirror and secondary mirror as a kit you are going to get them to about the right size for a snug fitting tube.
Once you have your tube you can go ahead and cut it to length. I cut mine 48 inches long. And you can cut it with a few extra inches if you want. That is quite ok.
Let’s look at some tube buying options.
6922-03 12 in.X4 ft.Quik-Tube
You can use a product called Quikrete tube. But I am not sure about the sizes of these tubes. They make 8″ 10″ and larger. This 4 1/4 inch telescope I am making would use a 5 or 6 inch tube so you have to check see if they have that size. They carry lots of these at every hardware store and Home Depot and Lowes. Bring a measuring tape with you because this kind of tube varies a lot in actual diameter. the 8 inch tube can actually be anywhere from 7 to 9 inches. So just pick through them and find something suitable.
Blacklite Telescope Tubes – This is a company that makes Telescope tubes with Kraft Paper. Much stronger than cardboard and these tubes are specifically designed for telescopes. I don’t think they carry tubes for 4 inch telescopes but they do have them for 6, 8 and 10 inch scopes.
Amazon does have some stuff but I am not 100% sure about it. They are Kraft tubes. But I can’t tell how sturdy they are. You can take a look at them here:
5 x 52″ Custom Kraft Mailing Tubes
Ok, now lets move on to making and installing the Mirror Mount
