ok i have seen some info that contradicts it self, i am going to build a 17" lcd projector but i want to know the point of the reflecter is it to focus all the light on one very small spot in the middle of the fresnel or to spread it out evenely across the fresnel.
thanks for oyur help in advance
thanks for oyur help in advance
To spread it out evenly.
That said, there are several different confusing reflector setups - the one that I'm going to use is the LL design, a metal halide lamp at the 'center' of a spherical reflector.
Spreading it out evenly isn't the only thing that has to be done, the fresnel should 'see' it coming from one spot, hopefully, in order to have a consistant focus. A spherical reflector does this well, without having to bother with extra lenses.
That said, there are several different confusing reflector setups - the one that I'm going to use is the LL design, a metal halide lamp at the 'center' of a spherical reflector.
Spreading it out evenly isn't the only thing that has to be done, the fresnel should 'see' it coming from one spot, hopefully, in order to have a consistant focus. A spherical reflector does this well, without having to bother with extra lenses.
so the light needs to form a cone starting from one point and ending up hitting all parts of the fresnel, so parabolic arc like on a satalite dish that focuses all the signal in one point would not work, nor would a diffuser used on a backlight on the origional lcd, just making sure by the way thanks for the fast reply
the entire light path
That's correct. The light comes from a small point just the size of the lamp arc. A spherical reflector is used to send more of the light back through the lamp arc toward the condensor fresnel. if the lamp is placed correctly, the reflector does not make the lamp arc look any larger.
The condensor fresnel captures the pyramid-shaped cone of light and refracts it to be perpendicular to the LCD. Then the field fresnel refracts the perpendicular light back to form an image of the lamp arc right at the optical center of the projection lens.
The LCD may be between the fresnels or it may be a few centimeters after both fresnels.
There are other ways to get a lot of light going evenly through an LCD and into a projection lens, but this is by far the simplest and most common design used in DIY projectors.
That's correct. The light comes from a small point just the size of the lamp arc. A spherical reflector is used to send more of the light back through the lamp arc toward the condensor fresnel. if the lamp is placed correctly, the reflector does not make the lamp arc look any larger.
The condensor fresnel captures the pyramid-shaped cone of light and refracts it to be perpendicular to the LCD. Then the field fresnel refracts the perpendicular light back to form an image of the lamp arc right at the optical center of the projection lens.
The LCD may be between the fresnels or it may be a few centimeters after both fresnels.
There are other ways to get a lot of light going evenly through an LCD and into a projection lens, but this is by far the simplest and most common design used in DIY projectors.
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