DIY-Projector Plans and theory collection !!

[mathias]

First I want to say this is a public diy forum, we share what we know and what we have learned, if you don´t want to share what you know, please leave this forum. Many people have leaved this part of the forum, and I will also do that, because here are very little new ideas, what people are doing today is just repeating of what other people have done many years ago. The only difference is that we have more high resolution lcd:s today, but in the same time commercialprojectors have been very cheap with the same resolution and better contrastrate.

I have here collected the most common projectorplans, some are cheap and some are more expensive to build. The difference in light output between the designs is about 40%. There is not such thing like 2-3 times brightness, if you get 2-3 times more lightoutput you have used wrong condensorlenses from the beginning.

Please share your projectorplans here and help me complete this
collection!!!

This projector design is the most common and use the parts from an ohp-projector, works with 250-575W double ended lamps. 65% of the light from the lamp will hit the fresnel.

[mathias]

This projector design is very cheap but is only for 1-ended lamps, the picture can be little dark in the corners. 80-90% of the light from the lamp will hit the fresnel.

[mathias]

This projector design is the best, very even light on the surface of the lcd, use one half of the slideprojector condensor and the other from a ohp. 99% of the light from the lamp will hit the fresnel.

[mathias]

This projector design use the parts from an ohp-projector, works with 250-575W double ended lamps. 65% of the light from the lamp will hit the fresnel.

[mathias]

This projector design is very cheap but is only for 1-ended lamps, the picture can be little uneven in brightness. 80-90% of the light from the lamp will hit the fresnel.

[mathias]

This projector design is the best, very even light on the surface of the lcd, use one half of the slideprojector condensor and the other from a ohp, you need two condensors from a ohp. 99% of the light from the lamp will hit the fresnel.

[mathias]

All platicmaterial reflecting a part of the light back to the source but in a other direction, this can easy been studied with a laserbeam. So use glass instead if you can, they reflecting a smaller part of the light.

[The Alchemist]

Great idee!!!! nice overview. Maybe we have to find examples of the specific projectors and also post them as examples.

In your pictures you say that the focal length of the objective is the same as the distance to the lcd, but i believe that it has to be just a little bit longer (240 mm objective ---> ~260 mm distance from tft to objective.)

I still wanna try the design of two half parabolic mirrors and a spherical one.



Maybe i will buy a raylight and test it.

[mathias]

Here is the most advanced projectordesign plans and also most compact, but most expensive. As you can see you must have pretty big mirrors if you want it most compact. You can use smaller mirrors if you move them closer to the lamp / object, but the distance will be bigger = bigger projector. You can use normal glass mirror on the lamp side, it can also be coldmirror to reduce the heat, but you can also have coldmirror build in to the lamp reflector (cheaper and more easy). The mirror on the objectlens side must be a frontsurface mirror otherwise you get ghosting, you can find these in ohp-projectors.

[mathias]

Mirrors are good, but what size do I need ?

In small lcd designs 5-7" you can not use so much smaller mirrors than the lcd size depending on that the light from the condensors lenses are almost parallel. But in 15-17" you can use much smaller mirrors than the lcd.