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How to Make an Eight Inch Reflector Telescope: Part 3 Making the tube

In this part of the tutorial we figure out the size of the tube we need and then make it!


Part 1 of this tutorial (the beginning) is here



Ok, so we now know that the focal length of our mirror is 29 inches. So now we can measure and cut the tube and add the parts.

We know that our mirror is eight inches in diameter. So we need a tube that is larger than that so the mirror can fit in it. I purchased a ten inch diameter tube from the home depot. They are very inexpensive at home improvement stores. But if you don't have access to one of those stores you can buy them online. They are quite a bit more expensive online because the large size adds a lot of additional shipping charges.

Quikrete Concrete Forming Tube 10

Quikrete Concrete Forming Tube 10 " Dia X 4 ' L


Let's figure things out.


The point of focus

Turn the knob on the focuser so the focuser is about half way out. And place the focuser on the tube.

Notice the red "X" I have placed on the picture.

With everything placed just as we have it, focuser rolled half way out, and the focuser on the tube. That is exactly where we want the focal length of our mirror to end. Right there.



So, the light path is from X to our mirror and that needs to be 29 inches.

diagram showing the focal length



Measure from center to eyepiece

Let's break down the measurements real quick. The "A" measurement is from the end of that focuser to the center of the tube. So go ahead and measure it.

It comes out to 9.25 inches. Easy enough.

So that means that measurement b will be 19.75 inches. The two total our 29 inches.


So now we know what size to cut the tube to. We will mount the focuser four inches from the end. Then we need 19.75 inches. To that point is where the surface of the mirror will sit. Then we add another four inches for the mirror mounting setup. So the total tube size should be cut to 27.75 inches. I cut mine to 28 inches.

The telescope tube dimensions



Cut the tube to the correct size

So go ahead and measure and cut the tube. Do a nice job. Keep that edge pretty clean.

Next Next we are going to fiberglass the tube to make it stronger. It is an optional step



Small telescope making kit

Science Fair Telescope Making Kit. Includes Cardboard Tubes and Lenses. 6x

Ideal for home projects and science fairs!Custom color-coded high precision paper tubing combines with a glass lens to create a genuine telescope in this easy to assemble kit. With step-by-step instructions, the kit leads you through construction of an actual telescope to view images upside down, just like in real telescopes. Assembled size: 14"L.



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