I actually bought this stuff a few years back. But for $9.95 i cant complain. The results were very bad indeed, but if your still interested email me and ill try and find the plans and scan them at school.
The lenses used in RPTVs are multi-element lenses, usually 4 lenses per color's barrel. The use of a fresnel single element lens is ludicrous by comparison, in terms of potential fidelity of image. The refraction alone degrades the picture at the edges, with rainbowing all over the place.
The intensity of the image in RPTVs is tripled by using 3 guns, none of which use a light-limiting shadow mask, as is used in directviews, to separate the colors. This is not necessary in monochromatic CRTs, allowing 2 to 3 times more light output per CRT, in RPTVs.
The light dissipation by using one fresnel lens on a regular DVTV will be directly proportional to the sizes involved. If the image on the wall is to be 4 times bigger than the source, it will be 4 times dimmer also. That is, when the fresnel lens is transmitting 100% of the light output of the source set, and when the wall is reflecting back a high rate of light output. Very optimistic.
Lastly, the lens turns the image upside down. All RPTV images start out upside down before they get to the screen they are sent to, which we look at.
If you try to turn your TV upside down, the purity will be hosed by the relative change in the Earth's magnetic field, until you turn it right side up again. The only correct way to do it is to redo the yoke connections inside the direct view, changing it to upside down on the source screen.
If you send it upwards at all towards a wall, you will also get keystone effect.
I tried all this about 30 years ago. "Disappointing" doesn't even come close. That's why I don't even think about this type of thing anymore.
I also tried the 27" fresnel lens in front of the 13" directview, which caused streaks going out from center, on anything bright. So much for taking a 27" magnifying glass to your DV and trying to call it a bigscreen.
Trust me, it's a silly waste of time. Even the worst mass-produced RPTV will give you a better picture.
Buy a large, perhaps 8-1/2 x 11 inch or more, sheet magnifying glass from a stationery or office store. Get a cardboard box large enough to hold the TV set (19 inch seems best, smaller means a dimmer picture and larger may be too heavy to manage) with space around on all sides for ventilation. Cut a hole in the box and mount the magnifying glass. Turn the TV upside down and face it into the box, using perhaps some books under it to prop it up but not obstructing ventilation slots. In a dark room you should be able to get a quite large although not very sharp and not very bright picture.