Projector TV

I kept seeing people selling lens + plans to build your own 100" tv on ebay and finally gave in and bought one. So what is this amazing fresnel lens then?? Nothing more than the lens found on an OHP and more commonly known as a page magnifier!

Here's a picture of some.

A couple of thought's

the picture will be fairly dim. since you're taking a bright, but small, tv image and enlarging it. and light obeys the inverse square law.
since the surface of most tv's are curved and you're focussing through a flat lens onto a flat screen, it's impossible to get the whole picture in perfect focus.

If you have any suggestions please add to my Wiki or email me.

My findings so far

I have only made a simple setup so far using card board and I have to say that I was surprised that it actually seemed to work! tricky getting it in focus - and am planning a wooden version soon. One problem is that if you turn your tv/monitor upside down your final image will fliped left to right - which i'm not happy with so am planning to use a mirror at 45 degrees and the tv on it's back to make it more like an OHP. also will try a second fresnel to focus more light from the tv to the second fresnel - again more like an OHP though they don't use a fresnel for the final focussing! There's a plan using two fresnel's here.

My First Attempt

Strangely enough... it only took ten minutes to build this one! Basically just a cardboard housing with another sheet for the fresnel.

Take a look at some projectors that people have built.
These are (apparently) example images, and find some more here.

The image produced by my projector actually isn't too bad, but my digital camera is no use in trying to capture it!

Someone Else's Findings

This text is nicked from www.skennedy44.freeserve.co.uk/projector tv.html which has some very sensible stuf about these projectors:

A quick experiment shows that the lens has a focal length of approximately 300mm. To find the focal length cast an image of a distant object on a suitable surface, i.e. cast a picture of a tree on the horizon, through the window onto a wall! You need the focal length as a starting point for dimensioning the projector. Lenses obey 1/f=1/u+1/v which means to project an image at infinity, the lens would need to be 300mm away from the TV screen and to project a same size image, the lens would need to be 600mm away from the TV screen. This gives us our focus range, you need to build the projector so you can move the lens between 300 and 600mm away from the TV screen (well, the 600mm is a maximum, and something less will be fine). Making a focussing mechanism is usually pretty awkward, you need to be able to move the lens whilst keeping it 'true' i.e parallel to the screen in this case. Also, as I mentioned earlier (if you've made it this far!) the picture will be reversed. The solution to this is to use a mirror and this has a convenient consequence, it allows making the projector more compact and allows the TV to just rest, picture down, on the projector.

Also, here's a local copy of some piccies of his projector.

Free Plans

Some miscellaneous instructions found on the net: