DIY Fresnel light

[infurno]

I have been playing with the idea of building a Fresnel light. There are some challenges to overcome but I think its possible. Obviously a DIY light should not cost as much or more then the real thing so I think the most important thing is to keep the costs down.

One of the most important parts of a Fresnel light is the actual Fresnel lens. I once built a video projector using a page magnifier, which is a plastic Fresnel lens. The plastic can be cut to a circle to mount in front of the light.

Unfortunately the plastic lens can deform due to heat, and render it useless but it has to get pretty damn hot first. I think some well placed ventilation holes, or if necessary a PC case fan to move some air would do great.

Here is a basic idea that I came up with, based on other Fresnel light models. Note that this is not well thought out, or to scale.

Basically the light socket is mounted on a support bar. The support bar is held in place by two rods and slides back by turning the focus control in the back of the light. The center rod is threaded, and it is what pushes the support bar back and forth as its rotated.

Im not sure what to use as a reflector though, but it should not be expensive or difficult to source.

If anybody has any ideas to contribute, would like to hear your thoughts.

 

[Spartacus]

Have you ever touched a hot fresnel???
I encourage most DIY projects, but a plastic fresnel?
Maybe there is plastic out there that can withstand extrem heat, but I´d rather look for a metal/alu housing and a cheap glas lens (and the later will be the hard part...)
Good luck!

 

[infurno]

In my DIY projector I used a 500W metal halide bulb (HOT) a few inches from the plastic Fresnel lens. The plastic lens did not have much trouble.

The case was cooled by PC fans but I think it just may work. Especially if using something like a 250w-300w

I think its worth a try, at least an endurance test.

Do all Fresnel lights use glass optics? I was under the impression some were plastic (acrylic or some other hard plastic).

The page magnifiers were made from an acrylic material, which holds up to heat very well. I think to melt it the temperatures have to get pretty extreme.

 

[infurno]

Also using an acrylic UV filter before the Fresnel lens will reduce most of the heat.

Past the UV filter it should only be warm, and reduce the chance of damaging the optics.

 

[hoarp001]

Mmm I think the ridges need to be bigger than those on a page magnifier...

 

[infurno]

Yeah thats one thing im worried about is the focal length. Im not an optics expert so I honestly don't know how that works.

What I did read is that the focal length of the Fresnel has to be where the bulb is located for it to work right. I don't think that will be a problem.

But it did work for my projector, and I think its the same concept. Acrylic Fresnel can be found online in different focal lengths.

I mentioned page magnifiers because they can be purchased at most local stores like Office Depot.

 

[Cool Lights]

All professional fresnel lenses use a borosilicate (high quality) glass lens with a real fresnel pattern on it which is far better at magnification than the plastic lenses. No real tungsten or metal halide fresnel I have ever seen used a plastic lens.

One problem with this idea is infrared. There is practically no infrared component in metal halide bulbs like those used in the projector you speak of. If your idea is to make a fresnel using a tungsten bulb I think you'll be very disappointed in the performance of the plastic lens and its failure as well. If you're making a metal halide fresnel, the plastic lens may work but I doubt that it will be very efficient. The infrared will most likely melt it if it is tungsten. I wonder, is the point just to construct a fresnel or to save money? Fresnels are available in the $200 range and they're pretty darn good too.

 

[infurno]

Your probably right. Earlier today I was calling lighting retailers across town looking for some sort of glass fixture Fresnel. Did not have any luck. I found some crude lenses at Home Depot but they were more like a glass bucket with a Fresnel pattern on the bottom to fit on a light. Monday I will try calling street lighting retailers, they may have what im looking for.

Its not that I can't afford light kits, I don't really need this light. But its the process of building it that I enjoy.

But im stubborn so im still going to run some tests

Im going to start by measuring the focal lengths of the rectangular Fresnel lenses I have available, and use the one with the shortest focal length. Hopefully I have something laying around which wont require an extended housing.

I got the prototype together yesterday, I will post some pictures later. Its got a housing and a moving element inside that is adjusted by turning a knob.

So far everything has cost ~$10 and took less then an hour to construct. Im missing the Fresnel, reflector, and bulb.

My temporary reflector will be some aluminum foil wrapped around the back end of the bulb. That should be enough to test with. Later I will source a reflector with the appropriate focal length.

So far the biggest problem I have run into is how many turns of the knob are necessary to move the element. It takes a little more work to adjust compared to my mole and other Fresnel lights

It will probably be Sunday before I have some time, tomorrow is a big production day.

 

[Jason Miller]

I'd like to see you're video projector

 

[infurno]

Here are some pictures from a test I just shot.

150w bulb. No reflector, so performance is only at 50% or less. Ambient light from florescent fixtures above.

Light off. Ambient only.

open faced.

Fresnel on. focused.

Fresnel on, scattered.


The good:
Well. It works obviously. Heat has not been a problem, components stay warm at best since im not using halogen bulbs. Did not keep it on longer then 15 min.

The bad:
Unlike my professional fresnel lights I cannot focus it to a more exact point then that. But Its not bad, in fact my 150w pro fresnels don't focus too much tighter then that.
[edit] never mind that, thats how it focused because its a frosted bulb, forgot A smaller bulb will focus a smaller area [/edit]

I think this is an overall success. The Fresnel gives a lot more control and makes this a versatile light.

Not much you can expect with ~$20 of parts and a page magnifier. I will post pictures of the light itself as soon as I paint it and do the final touches.