what is the fresnel lens used for the triplet lens allready projects the image onto the screen also can you use just one fresnel lens if it is needed at all

westward,

I'm going to take a shot at your question since it appears that we're the only ones up at this hour.

The guide clearly explains the role of each of the two fresnels. To recap:

The fresnel nearest the light source is intended to take the light at its focal point and spread the rays evenly across the LCD. In doing this it straightens the rays that exit the source radially and causes them to become parallel (perpendicular to the plane of the LCD).

The second fresnel, whether it is placed on the projection lens side of the LCD or the light source side, focuses the light rays exiting the first fresnel into the projection lens. This increases the light that is projected to your screen.

When the second fresnel is placed on the projection lens side of the LCD it can also be used to perform keystone correction by tilting it so that it is parallel to the wall/screen surface.

Hope this helps your understanding. If it just confuses you, ignore it. I'm sure brighter minds will chime in at a later hour.