Square light beam?

[nez]

Hey guys,

 

I'm trying to create a large square column of light that has the same diameter all the way down. This is proving to be extremely difficult. I was wondering if anybody had any ideas of how this might be created?

 

Although not square would theater lights be able to achieve a spotlight that doesn't gradually expand as it moves further from the source or is this just going against the laws of light?

 

Any input would be extremely useful!!! Thank you.

 

Nez

[moth]

maybe a parabolic reflector with the light at the focus. if the maximum diameter of the reflector is larger than the beam you want,you can use a square mask that should stay somewhat collimated.

[coke]

This can kind of be done by using a convex lens in front of a small light bulb or as moth said, a parabolic reflector behind it...

Place a square cut-out past the lens or on the other side than the reflector, and move the lens or reflector forward and back until you get a square beam of light that keeps from diffracting.

 

I would think theater lights are parabolic reflectors (because they would require some rather heavy lenses otherwise), they should work... if not a uniform beam, it still probably doesn't diffract too much.

Edited April 6, 2009 by coke

[Cap'n Refsmmat]

Diffraction would cause the beam to spread out -- even laser beams spread out over a distance -- but you could make it fairly narrow with a parabolic reflector.

[Klaynos]

Over what distance are we talking about?

 

Without using a laser and an aperture you will never achieve good collimation over a long distance as there is a finite light source at the focus of your collimating optics.

 

As well as diffraction as Capn' says.

[nez]

Thanks for the answers.

 

Ideally the beam will stretch 7feet in height and would be one foot in thickness. can you get parabolic reflectors that will work on this scale or would a laser light be better suited to the task?

 

Thanks again

[swansont]

You won't be able to get a super well-defined rectangle, but using a cylindrical lens will expand a beam in one direction. You can also use anamorphic prism pairs to do this. 7 feet, though, means that you will want to use mirrors rather than lenses.

[nez]

Hi swansont, thanks for the reply. So do you think the best option would be to a laser light with mirrors? do you mean use the mirrors to enhance the strength of the beam?

 

Thanks

 

Neal

[swansont]

Hi swansont, thanks for the reply. So do you think the best option would be to a laser light with mirrors? do you mean use the mirrors to enhance the strength of the beam?

 

Thanks

 

Neal

 

If you are expanding it the intensity is going to decrease. But yes, I think you need to use mirrors for something on this scale. It should be cheaper than lenses, unless you can get Fresnel lenses that big (I've never run across any bigger than ~ a meter)