# I How to project a high power white line

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1. Dec 19, 2017

### Domenicus

Hi

I have a personal art project and I am stuck, because of very limited knowledge.

I'd like to project an 1-2 meter white line from 1-3 meter distance. The projected line should be as thin as possible (3-10mm) and as powerful as possible. I created a DIY projector, but my problem is that, the line is not thin and powerfull enough. I am in process of adding cylindrical lens to focus most of the light on the slit, but I am afraid it won't be enough.

I'd appreciate if you could give me some idea of a different system or improving this one. My budget is somehow limited.

See the image of the projector, I've created.

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2. Dec 20, 2017

### Staff: Mentor

Does it have to be white? There are commercial laser alignment systems that make bright lines, typically red and just 1-2 millimeters wide.

It might be possible to convert that to white light, or to modify these systems.

3. Dec 20, 2017

### A.T.

You have to focus it at the wall.

4. Dec 20, 2017

### Nidum

Flying spot .

5. Dec 20, 2017

### Domenicus

Thanks for the ideas, they are all good!
White would be good, but colored ones can be an option as well. I just have to see if these layers are harmful to human eyes.

This could be an option, than I don't have to use camera lens. I will cast resin lens (the glass ones are expensive). Here the only problem is the light source.

This sounds a bit complicated, but I'll try to find an already made product, which I could use/adapt.

6. Dec 22, 2017

### sophiecentaur

Apart from the moving parts, the flying spot solution is way easier to get a good, bright line than any home made optics. A "cast resin lens" would almost certainly disappoint you with the sharpness of the line and general Flare. If you want a straight, projected line on a wall and could put up with a red or green line, a builder's laser level would do the job fine. You could choose the length of the line by operating the laser level in an enclosure with adjustable sides to shutter the beam.
The best solution would depend on the brightness and length of the line you want, of course. Your initial attempt shows the problem of a simple solution because the ends of the line are not very well defined. You could limit them with a shutter but would it then be long enough?

7. Dec 23, 2017

### CWatters

You don't want to focus it on the slit because beyond the focal point the light rays diverge.

For best results you want a point source (small filament) and a large distance between the source and the slit so the rays passing through it are nearly parallel.... or lenses to achieve similar.

8. Dec 23, 2017

### sophiecentaur

Any light that doesn’t go through the slit is wasted. The slit is an object which must be projected on the wall. A proper condenser system ensures that the light focused on the slit nearly all diverges over the projector lens aperture. The condenser uses a diverging lens to achieve this (Not perfectly tho’) by putting the light source virtually a long way back.

9. Dec 23, 2017

### sophiecentaur

That's not all correct. OF course, it's necessary for most of the light from a projector lamp to go through the projector lens so the bulb needs to be focussed at the exit. At least, that was the way things were when projector lamps had a large rectangular filament array. In halogen projectors, the point source is focussed at a point beyond the projector lens - to fill up the exit pupil. I mis-remembered about conventional condenser lenses, which are large diameter back to back plano-convex lenses. But a conventional projector system is not what's needed here. all / most of the light from the bulb needs to pass through the slot, as I said. If all the light from the bulb is to go through the slot, a cylindrical lens would be needed to modify the illumination to fill the slot.
But I think conventional projector optics would not be best.
Now I am remembering a tatty old laser level that I was given years ago. There is a device that you fit on the end of the laser which produces an excellent uniform line. I guess it's a hologram pattern of some type. All the cheapest levels must work this way. No moving parts. It's something that you could borrow from a friendly DIYer and you could experiment with a narrow white light beam (which is much easier to produce.) You could always use red green and blue laser pointers side by side and superimpose the lines they produce. Once screwed down on a solid board, your line would be a pretty good white.

10. Dec 24, 2017

### Domenicus

Thanks sophiecentaur for the detailed feedback.

The handmade resin lens will work only with the setup in the picture -> focusing much of the light on the slit. In this case the flare is not a problem.
The end of the lines don't have to be perfect, what is important to project this line from 1-4 meter and to have 1-2 meter lenght 1-10 mm thickness.
I've searched this "flying spot" tool, but I've found only in short distance scanning setup.

I need this bright line in long exposure photography. I did few self portraits, but I'd like to make full body photos with faster moving subjects and that's why I need more powerful light.

11. Dec 24, 2017

### Domenicus

Thanks. I've put tracing paper on the slit to avoid this problem, but I want to try diffused glass plate to have more light on the slit...if I continue with this setup.

12. Dec 24, 2017

### Domenicus

Thanks again sophiecentaur

I will improve the actual system by trying to focus much of the light to the slit. I have to dig in in more into optics. A condenser lens is a good idea to make the light beams more parallel, than when they go through cylindrical lens the focused light will be thinner.
In a second phase I will try the white laser with the hologram thingy, I just have to be sure, those laser are not harmful to the eyes, since I am projecting on people. I saw some laser projectors and their creators claim that it is not harmful to the eyes, so this laser setup could work as well.

13. Dec 26, 2017

### pyroartist

14. Dec 26, 2017

### Staff: Mentor

That's what I suggested in post 2 already. They are typically red, not white, however.

15. Dec 26, 2017

### pyroartist

mfb: Not to be picky but in post 2 you did not suggest a "laser level". You suggested "commercial laser alignment systems" which sounds like some type of a complicated and expensive instrument.
Also, in post 5, the original author said colored light would be OK.
"White would be good, but colored ones can be an option as well."

16. Dec 26, 2017

### Staff: Mentor

One of the first google results for "laser alignment systems" is one for $36, and if you take the ebay link you also get something for less than$10. Maybe "laser level system" is a better expression for it and gives you a higher fraction of good results, fine. I expect some ability to look through search results if someone wants to buy such a system.
What you think it sounds like is up to you. I think it should be clear that I wouldn't suggest very expensive devices without a comment about their price - and I didn't make such a comment because I know there are cheap devices.
"can be an option". Being red is still a disadvantage.