I have been playing with fresnels, for a while now. There is alot of bad info out there. Some people blindly believe that the highest groove density is all matters, or use the biggest size lens. These can sometimes negate the very reasons for using them, in the first place. You could end up with a focal length a couple inches in front of the screen. (Although, it looks like Kimchoc1's problem is just the opposite.)
One of the reasons for using a fresnel is to create a larger display. A well designed lens should make it seem that your monitor size has doubled. (Not that the lens is double but your perception of the magnified image is.)
The second is the sense of distance it provides. The lens make the display seem larger but farther away. This gives the brain the "depth of field" cues it needs, to fool it into thinking it is looking outside and past the monitor. This also forces the eye to re-focus, when looking at stuff inside the cockpit. It's suprising the level of realism that this provides.
As a side note, that is why I have pressed for advances to the multiple display handling and other cockpit builder's type improvements, in EECH. If you notice, in Kimchoc1's pic, he is using MSFS. So, he can put his instruments on the 2nd display. This allows him to take advantage of the "depth of field" cues, when switching from the outside and inside views. Aside from a more realistic controls layout and some switches, you can't complete a decent EECH cockpit without moving the MFDs to the 2nd monitor. As it is now, you would have to pan down (or switch the view) of the primary display to see them. Since they are still behind the fresnel, they are also magnified and the cues are lost. (It's a damn shame someone smarter than me can't figure this one out!!!)
One big problem with fresnels is stray light. That includes light on the front and the back of the lens. The fix for the front is easy... Add a small 3"-4" hood around the sides and top edge of the lens housing. For the back, there is more too it. Excessive light in the back creates the kinda washed out effect that some people complain about. This can come from the monitor's light bouncing off of the side of the housing and off of the back of the lens itself. The best fix for this is to buy an AR (anti-reflective) lens and to make the inside of the housing as dark and sealed as possible. (Matte black paint will work but thin sheets of black neoprene rubber are the best!)
After exhaustive research, here is where I get my lens from.
http://www.icetec-uk.com As well as selling decent priced AR lens, their site does an excellent job explaining fresnels. They sell pre-made housings, too. Although, the lens come with plans to make them yourself, for alot cheaper. But hey, if you're lazy....rock on.
Design FYI - The lens are about 11" square. They will work on a monitor up to 21". They mount about 8" in front of the screen and your face needs to be about 13" in front of the lens.
They're also including plans now, for some wacky head-mounted fresnel design. It's not for me because it eliminates the whole depth of field thing but apparently it gets rid of the edge distortion and allows for variable magnification. (To me, it sounds like a headache waiting to happen but it might be for somebody.)
Another site to check out is:
http://www.bugeyetech.com They are WAAAAYYY overpriced but just checking out the design of their housings may be helpful for the enterprising builder.
Hope this helps!
Tim