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Hi I noticed that some people that are using the smaller lcd's seem to be sandwhing the fresnels together and focussing the light on the triplet and then placing the lcd between the fresnels and the triplet. This (in theory) seems like a better way of doing things, or am I wrong. This way your light is collimated before it goes through the lcd and yet you do not need to go through another fresel after the lcd is in place. This seems like it will reduce distortion that may be caused by the "fresnel" rings. Is this totally not a proctical way to work with the larger lcd's because larger fresnels would be needed and a larger box? Or am I missing something else. Because if size is the only issue then I wouldn't mind as my projector will hopefully be mounted in a wall.
Anyone got any more knowledge they can throw my way on this issue?
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question about fresnels
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Posted 06 November 2004 - 03:44 AM
TuxLux, on Nov 5 2004, 08:09 AM, said:
This way your light is collimated before it goes through the lcd and yet you do not need to go through another fresel after the lcd is in place. This seems like it will reduce distortion that may be caused by the "fresnel" rings.
The reason for putting the second (field) fresnel after the LCD is so that you have truly collumated light passing through the panel, thus maximizing light transmission.
If the second fresnel is before the LCD the light is angleing back toward the focal point and is not actually collumated and you will lose brightness.
Distortion from the fresnel is not a problem unless it is placed too close to the LCD where the triplet will focus on it.
Plus, with the fresnel after the panel you get the added benefit of keystone correction.
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Posted 06 November 2004 - 06:31 AM
DeathRay64, on Nov 5 2004, 10:44 PM, said:
The reason for putting the second (field) fresnel after the LCD is so that you have truly collumated light passing through the panel, thus maximizing light transmission.
Exactly. LCDs tend to transmit light best when the light is going through them at 90 degrees. Straight through them. Any angle on the light source tends to reduce its brightness.
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