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Projector length of tube? Answered

I was curious if it's possibly to extend a projected image, from a projector (like tv/computer) down about a foot of tube. Tube would be 1 - 2 inches wide. If this isn't possibly what would be the smallest width the tube would have to be for it able to go down a foot of length?



Best Answer 5 years ago

Wait, what? Maybe I'm wrong, but a "tube which carries an optical image" is commonly called a telescope. A writeup on refracting telescope design will tell you how to choose the lenses at each end, based on the length of tube, and where your eye will be placed relative to the eyepiece.

Sounds like I'm heading in the right direction. I replied to Rick. So to understand all I need to do is feed the beam straight down the tube, by bending the light/picture, then at the end add the correct lens to spread the image out. That sounds doable.

I'm not sure what you mean by "bending the light." Telescopes are straight, by definition, because light rays do not curve while they are travelling. The lenses will bring the rays to a focus, but not redirect the image in a different direction.

If you want a flexible tube, you should look into borescopes, in which the objective lens is optically joined to a large optical fiber, with the eyepiece lens (usually a camera) at the other end of the fiber.

I think we're going a little away from what I want. I won't be looking into the tube at all. I want a projector that will be hooked up to a computer to project though the tube. I planned on building the projector, but projecting the image though that long of a tube with a small dimension I feel is hard to do. But I don't think it's impossible.

Oh! That is much, much easier. It sounded (from one of your comments) like you want to attach a viewer of some sort to a mask. Sorry for the confusion.

You basically just want a long telescope attached to the front of a projector? That's really easy; it's just a funky telescope design with a long focal length on the eyepiece.

Ah thank you, sorry for the earlier confusion. Hopefully in a few months the outfit will be done and I might have an instructable on what I did.

Effective projectors need a high-power light-source, like a hi-watt halogen-bulb - can you fit one in?


I will be using a high end LED. I'm not planning on projecting anything huge, probably at most 10 feet in front of me or less. The projector itself wasn't what I was worried about, just the length of how far the image had to travel before it could be spread out.

You also need lenses, to answer the question (how far the image had to travel before it could be spread out) - you need a big and hot thing to get it to go far sharp and bright. In a blackened-room it might be good at 3 feet with a high-end LED. That's a guess.


Well when I finish it, I planned on sharing it.

I am really unclear what you want to do.

You can project an image using a lens system. The diameter isn't directly relevant then - It affects the light gathering capacity.

To give a better idea, I plan on making a Boba Fett outfit. I want his eye sensor thing (the thing that comes down and helps him aim) to be a projector. By lens system do you mean instead of an pop out eye do an inward eye, then at the end do the pop out eye? That sortof makes sense.

So, confirm you want to make a heads up display?

No? I did a quick search on google for "heads up display". What I want to do is build a projector, that would normally be used to watch tv/use the computer, inside a helmet for a costume.

Lastly clarify - Do you want to look at an image inside the helmet, projected into your eye, or do you want to project an image on the scene around you that everyone could see?
If the former,
Right, a projector that goes directly into your eye is called a heads up display, also known as head mounted display, or wearable display. In those sizes the optics are practical, but difficult for the average end user - it's why the military uses them at tens or hundreds of thousands of dollars each -- they are very very difficult to engineer.

The difficulty arises from a) having a small enough display to reasonably shrink to a focus-able image close up to the eye, and b) getting the specific optics to get the job done. Cameras have done this for years - if you salvage the optics from a lcd-viewfinder from many newer point and shoots, and figure a way to interface with the internal lcd you'll be golden. (Newer single mirror digital slr cameras use a target lcd instead of 2 mirrors to show the view through the lens).

If it's just a projector to put a picture on the scene around you, go with a commercial solution. You can get pico-projectors now that are reasonable cost and save you all the headache.

It's the former, I want to be able to project it on a wall for other's to see. But now I'm really interested in trying the heads-up display. But that might be way later in the project. I will definitely look into the pico-projectors, but I still like the idea of making it myself.

A projector that can hit a wall 10 feet away with any brightness is going to be a good 10 pound full size projector -- all the picos are less than a pound but only good for a 40 inch screen in a dark dark room.

Well I plan on doing it anyway. A 40 inch screen, or even a smaller screen is fine. I don't plan on doing much with it. It's more for looks.

The width of the tube assuming it comes from a projector would have to be conical, the shape of the projected image, and the width would have to be at the size of the furthest cross-section. The optics are very delicately balanced and focused at the factory to provide a uniform throw - if you go adding optics to compress then re-enlarge the image you'll lose quality, guaranteed.

Why on earth would you want this anyway?