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i took apart a projection tv and was thinking of selling the lenses i hear they can melt padlocks and stuff is that true? im going to sell 2 i was wanting to know if they sell fast and what to sell them for? oh and i hauled the tv on my hand truck i used the cart form instead of the 2 wheel cause this thing thing was huge 60in maybe i was not liking it when i went over bumps but i did have 2in ratchet on it so that was good. you guys have any luck selling them fast?
They're called fresnel lenses. Never really messed with them myself but you can google them along with projection tv and get an idea
I don't think the rear projection TVs have Fresnel lenses. https://en.m.wikipedia.org/wiki/Fresnel_lens
Inside there's three lens setups & if you are taking the Cast Ali end off, beware, there's a lot of a thin clear oil inside it. You can pop the rubber bubble to drain most of it out first.
The front plastic clear screen has a texture to it that's similar to a Fresnel lens, but it's just vertical lines made to concentrate & then spread the individual pixel spots.
I think the confusion comes from a 1960's -70's gimmick you could buy, it's a big sheet plastic Fresnel lens which you could mount in front of a smaller TV 14 - 21 inch screen, and it would magnify it up to 26-29 inches.
It was only good if you were directly in front of it & didn't mind a colourful aurora thru the picture ( that probably didn't matter much in the late '60's, maybe it even helped...)
I have seen a much smaller A4 size version sold as a 'Vehicle rear window reversing lens'.
And yes, they will heat up something extremely fast with just sunlight, even if it's unfocused.
At the same time, those lenses in the rear projection screen TVs. I left one on my passenger seat during the day.
When I shifted it I found a thin arc of burn marks across the seat, right thru the material.
You can actually see the sun's movement thru the whole day & where it was brighter & overcast as the sun moved thru it's arc.
I'm lucky it didn't catch on fire.
I don't think the rear projection TVs have Fresnel lenses.
Inside there's three lens setups & if you are taking the Cast Ali end off, beware, there's a lot of a thin clear oil inside it. You can pop the rubber bubble to drain most of it out first.
The front plastic clear screen has a texture to it that's similar to a Fresnel lens, but it's just vertical lines made to concentrate & then spread the individual pixel spots.
It think the confusion comes from a 1960's -70's gimmick you could buy, it's a big sheet plastic Fresnel lens which you could mount in front of a smaller TV 14 - 21 inch screen, and it would magnify it up to 26-29 inches.
It was only good if you were directly in front of it & didn't mind a colourful aurora thru the picture ( that probably didn't matter much in the late '60's, maybe it even helped...)
I have seen a much small A4 size version sold as a 'Vehicle rear window reversing lens'.
And yes, they will heat up something extremely fast with just sunlight, even if it's unfocused.
At the same time, those lenses in the rear projection screen TVs. I left one on my passenger seat during the day.
When I shifted it I found a thin arc of burn marks across the seat, right thru the material.
You can actually see the sun's movement thru the whole day & where it was brighter & overcast as the sun moved thru it's arc.
I'm lucky it didn't catch on fire.
You don't need these lenses to melt, if you will, a padlock. It can be done with gallium. There are plenty of videos on Youtube about the remarkable characteristics of gallium. Just a few of the many:
https://www.youtube.com/watch?v=EQWO33MCZVo (gallium dissolving a Coke can)
https://www.youtube.com/watch?v=k919f7Qi4es (opening a padlock with gallium)
https://www.youtube.com/watch?v=9AR5ZIEYqT4 (pouring gallium on an iPhone)
Just don't accidentally pour it on your pants...
#### double post lol.
I was trying to add to the post that the big mirror inside is a 'Front Silvered mirror's.
Instead of the Silver being on the back of the glass, it's on the front of it.
That's because if it's on the back there would be a slight mirror effect off the front of the pane of glass. Leading to a slight double image n the screen.
The mirror can be used to make a 'True mirror' if you like a little woodworking joinery project. It's two mirrors touching each other, but set at 45° & in your reflection you get to see your own face just like everybody else sees it.
In a normal mirror, your image is reversed, a right hand part in your hair looks like a left hand parting.
You actually look quite different from what you think you look like.
You can make one with a normal mirror, but you get a gap down the centre where the mirrors join.
https://en.m.wikipedia.org/wiki/Non-reversing_mirror
yeah i kept the mirror thing neat its like a no glass mirror pretty cool. so it is oil in them thats what i thought.
Yep, there's oil in them.... Lots of people, including me, have been caught out by opening them over carpet, concrete or wooden floors..
Lots of oil & when it starts pouring out it seems not to stop until it's empty.
some tvs have a large square or rectangle flexible lense. they can start fires
In my own personal experience - back when the televisions were still being made, they could sell for $20+.
Now-a-days folks use them for solar water heaters, and they sell for $1 to $5 each.
https://i.ytimg.com/vi/wprlzCDfLm8/hqdefault.jpg
thats crazy never seen one of them lol.Quote:
Originally Posted by RLS0812
They are a ton of fun and easy to make. I have given them to local schools for science projects, or have made my own solar heater and still. I always have extra wood around.
Are your 100% sure it's a Fresnel lens in those projection TV's?
I have never found one in the ones I have scrapped out.
I have found a similar plastic lens, but it's parrallel vertical ribs in it & its there to help stop individual pixels from blurring into each other, and to mix the pixel image properly to get the right colour. ( There's probably a better description of what I'm thinking that it does per pixel )
I have another one I can get to too double check what the screen is like. The Fresnel lens I have definately come from a gimmick used to enlarge the screen of a small tv.
Oh, I just realised, there's YouTube instruction videos of this. You can use the projection TV individual lens arrangement to make a projection TV from a small TV & maybe a computer monitor.
It involves making a wooden box to hold the (CRT) TV & the lens setup, this projects the TV maybe onto a wall or such.
The image is 'Reversed', so words end up spelt backwards, but you can utilise the mirror to fix that.
It's a bit old-school, re the CRT TV, but a inventive person could use a LCD monitor, or use it in similar ways for its effects.