Dark rings

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I'm building my projector and when I installed the second fresnel (the one between the LCD and Lens), I have big dark rings. My setup is a 15" screen, 250w MH with a reflector, 2 330mm fresnels and 135mm triplet from DIYLabs. If I shorten the distence between the light and LCD it works great and the image is very bright and clear but now the distence between the light and LCD is about 9".

Please help.
 
In my projector I initialy had a fan blowing right on to the LCD to keep it cool however dust build-up was evident with in a couple of days

so make sure you place your fans smartly so dust doesnt collect on the LCD.

You might want to seperate the bulb and the LCD with a peice of glass..... this will make a 'light compartment' of your projector which you can cool independantly .... if you wanted to get really fancy you could get two sheets of glass with about alittle less than 1/2" between them seal around the edges...... except for the left and right of the bottom where you would insert that plastic fish pump tubing then fill the enclosure with water making sure there are no bubble; attach the two tubes to a heatsync/ pump and the water would disipate the heat. Making for a very effective cooling.... I havnt accualy tried this but have thought about it several times.
 
I have enclosed the bulb assembly in a metal box (which was the original box of the overhead projector) and the heat inside the box is exracted by a separate exhaust fan, the light ocmes out a sheet glass. With such arrangment least heat reaches the fresnel and LCD. Futher the LCD is aircooled by another fan blowing outside air. The dust collects on LCD, which can be cleaned once in a month. All these details can be seen in our web page. The results are excellent and have been appreciated even by experts.
 
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