Sunday, 14 February 2016 10:39

## How to Make a PVC Telescope

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### Step 2: Determine Focal Lengths, Determine Pipe Length

The lenses want to be situated in the telescope the sum of their focal lengths apart. In other words if the focal length of one lens is 6" and the other is 4" then they want to be 10" apart in the telescope.
The 3d printed fittings won't be long enough so you'll need a length of PVC pipe to make up the difference.
While there are a number of ways to determine the focal length of your lenses, and calculate what length of pipe you will need, the easiest way to figure it out is to just line up the lenses and look through them both, adjusting the distance between them until you see a clear magnified image of something across the room - no calculator required.
Take note of about how far apart the lenses are. In my example its about 10" (even though the picture shows a different measurement - I was experimenting with a different set of lenses).
The lenses want to be 10" appart, each fitting is about 4" so an additional 2" of PVC pipe is needed plus we want the pipe to engage the fittings by about an inch on each side and leave room for adjustment, I've made this example pipe 4.5" long 