DIY-Projector Plans and theory collection !!

[mathias]

We need a frontsurface mirror on the object side, but what size do I need, they are very expensive, so do the one in my old ohp-projector fit ?

I have done a calulation example so just follow it and you will get the right size.

[ace3000_1]

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.

Not true, it depends how far you place the mirror from the lcd, just like how the ohp's mirror is so far away wich in turn alows it to be small.

[ace3000_1]

mathias, i hate to disapoint you but your drawings are wrong with the condensers lol, sorry to have to break the bad news but dual condensers work as the pick below.

Imo i like your mirror drawings, nice work.

Trev

[Hezz]

Actually,

I think you are both right. The real problem with lens schematics is that they are so oversimplified as to be almost misleading. There are usually many millions of light paths through the lens. And there will rarely if ever be one simple scheme or focal point. The best you can hope for is to get most of the light to a common focal point. The fact is that positive plano lenses or similar lenses collapse the light beam no matter which way they are oriented. So where the light focuses depends on the angle of the light. However there is a light reflection issue which sometimes effects the orientation of the lens because the closer the light ray is to perpendicular to the surface it enters (or perpendicular to the tangent of a curved surface) the less light will be reflected back. So that is why there are often preferred orientations. The higher the angular incidence that the light ray hits the surface more light is reflected up to a maximum amount of reflection that is specific for each substance. This angle is usually around forty five (but not exactly) degrees for many types of glass.

For this reason you will almost always see the first positive surfaces of lenses rather large curved so that the light rays coming from larger angles hit the lens surface at a more desirable angle thus reflecting less light back.


Hezz

[Aidan Isaac Lev]

@hezz. Very informative post Now i think i undesrsand y some projectors have dark corners.

[mathias]

mathias, i hate to disapoint you but your drawings are wrong with the condensers lol

Like Hezz say we are both right, and my drawings are NOT wrong, if you have parallel light coming from the lamp they work in the way I have drawn. You have a POINT source and then they work in the way you show .

[ace3000_1]

However there is a light reflection issue which sometimes effects the orientation of the lens because the closer the light ray is to perpendicular to the surface it enters (or perpendicular to the tangent of a curved surface) the less light will be reflected back. So that is why there are often preferred orientations. The higher the angular incidence that the light ray hits the surface more light is reflected up to a maximum amount of reflection that is specific for each substance. This angle is usually around forty five (but not exactly) degrees for many types of glass.

Hezz and thats exactly right, and its why ive got my condensers coated in anti glare, the anti glare have a much sharper light then with the same without the anti glare, the one with the anti glare is somewhat brighter too as more light is going where we want it.

As for the angles thats where reflectors come in, its not just a matter of getting a spherical reflector, the focal is very important to obtain maximum light from the bulbs light transmision pattern, to get the desired angle through the condenser, and to the frensel at your desired focals for maximum efientcy at the coresponding angles required, even the depth of a spherical reflector matters to get the ultimate desired results.

Trev

Trev

[ace3000_1]

if you have parallel light coming from the lamp they work in the way I have drawn. You have a POINT source and then they work in the way you show

Im not talking about the paralelle light ones, i am talking about the point source pics otherwise i wouldnt have posted the way 2 condensers work with a point source.

Also hezz is talking about miss matched light, there is no way u will get rays out of a positive power lens in the way you show it, paralelle or non paralelle light, the light will go to the focal point of the lens.

Trev

[mathias]

Trev, all drawings use the technics from professional design and I don´t understand why you say they don´t work.
Many of the designs is taken from physics books, and I promise you that they don´t have wrong! The ellipticalreflector design is used in all modern slideprojectors with a lamp of the type ELC A1/259 with built in reflector. And the other designs use the normal ohp-design.

And if you say these design are wrong I suggest that you draw a right one.

[ace3000_1]

Mathias this stuff has been posted in here a few times and argued about before, i dont have time right now to draw up a pic but i will do abit later on as i have some serious work to do and not enough time. Have a read in here. there are manny formulas and they tell u how basic lenses work, although imo not for the beginner.

http://www.edmundoptics.com/TechSupp...?articleid=267

You can always ring them, ive rung them up before, they are more then willing to help and are all optical engineers.

Trev