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150 inch TV's for $20???

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150 inch TV's for $20???

Postby gigabyte on Sun Nov 23, 2003 1:48 am

Hey, I was just surfing on the net when I came across a site where you could buy a method to build a projector for like $20 and it will make your tv like 150 inch or sumthin, do i searched on google, and there are many sites like that, but you have to buy them all. Anyhow, I thought it was kinda neat, but I'm no genius, so I don't know if it's good or not or anything, so I decided to post a bunch of websites here and see what all you people think:

http://www.books4you.addr.com/TvHowToMa ... ector.html
http://www.psreporter.com/big_screen_tv.php
http://www.maxtheater.com/
http://www.psxnation.com/myimax/
http://www.gobigtv.com/
http://www.tvplans.com/

What are all your thoughts on this??
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Postby Matt on Mon Nov 24, 2003 10:40 pm

One of my co-workers is attempting this with a 21" tv... I'll let you know how it turns out.
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Postby gigabyte on Mon Nov 24, 2003 11:28 pm

Alright, also, could you let me know where he got all the materials and instructions and everything from? Because if this turns out to work well, I may consider trying it out... please keep me posted!
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Postby cfitz on Tue Nov 25, 2003 12:28 am

The best you can hope for is a dim image. The worst is a blurry, distorted, poorly focused, color-fringed, dim image.

It is certainly theoretically possible to focus the output of a TV through a lens to project an image on a screen. That's just basic optics, and how most of the large screen TVs work. However, the fundamental problem with this scheme is the limited brightness of a conventional television tube.

When you take a 20" TV and expand its image to 150", you are magnifying by 7.5x on the diagonal. That is approximately a 50x increase in area. With 1/50'th the light per square inch, the picture will be only 1/50'th as bright as normal. And that isn't counting all the losses through the lens and the reflecting screen. Guesstimate 50% losses (mostly in reflectance from the wall) and the picture is only 1/100'th as bright.

Will an image 1/100'th as bright as normal be usable? In a dark room it should be visible, although not with vibrance. Expect it to look dim and washed out. In a brightly lit room with windows open to the sun as shown in this "artist's rendition" from www.books4you.addr.com?

Image

Not a chance! These jokers ought to be paying fines for false advertising (they have some other doozies on their site as well).

Okay, let's say you can live with a dim image. What about the quality of that image aside from its brightness? If the lens they provide you isn't high quality, then you will suffer from all the other defects I listed earlier: general blurriness, visible distortion (e.g. straight lines are curved), poor focus (e.g. you can focus the center or the edges, but not both) and color-fringing. Now ask yourself why cameras and real projectors (both TV and film) have computer optimized, multi-element, anti-reflection coated lenses ground to precise concave/convex shapes from optical quality glass instead of a single Fresnel lens, and then further consider how much quality a $15 pressed plastic variant of a Fresnel lens can have...

Oh, one more thing. If they only use one lens in their projector plans (which I can't say for certain since they don't reveal their plans, but which I suspect from looking at the pictures and reading some of the text), then the image will be upside-down and reversed left to right. There are two ways to fix this: stand on your head while viewing or flip the television upside-down. Flipping your television isn't very convenient, but it is probably better than standing on your head for most people. However, the subsequent build-up of heat inside the cabinet doesn't bode well for the long-term health of your television (particularly if you have the brightness cranked up in an effort to compensate for the dimness of the magnified image). There is a reason for all those slots on the top of your television cabinet...

All in all, these plans are nothing but schemes to separate you from your hard earned money. They supply you with a product that is just barely functional enough to keep them from going to jail for fraud, but not something that you will be happy with. Save your time and money for something better. Of course, if you have already purchased a kit, don't fret. That Fresnel lens might not make a good projection TV, but it makes a heck of a good magnifying glass for frying ants on a hot summer day... :)

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Postby gigabyte on Tue Nov 25, 2003 12:34 am

LoL, wow, that game is HILARIOUS! Anyhow, thanks for your input on this topic! Wow, a really long response!
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Postby cfitz on Tue Nov 25, 2003 12:40 am

You're welcome. And don't forget to get the poodles... :wink:

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Postby Dartman on Tue Nov 25, 2003 2:28 am

I typed a similar response earlier but I backed out and lost it so I gave up.
I guess it's be worth 20 bucks just for the poodles though :o
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Postby cfitz on Tue Nov 25, 2003 2:31 am

Dartman wrote:I typed a similar response earlier but I backed out and lost it so I gave up.

Ouch! That's frustrating. When I get working on a long post I normally move it to a word processor and save it to disc. I've developed a life-long Windows habit of save early and save often...

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Postby UALOneKPlus on Tue Nov 25, 2003 4:21 am

cfitz wrote:... I've developed a life-long Windows habit of save early and save often...

cfitz


THis is true whether you're talking about data or money!!
LOL :lol:
"Life is a great big canvas, and you should throw all the paint you can on it."
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Postby dodecahedron on Tue Nov 25, 2003 7:32 am

damn, it's a LONG time since i heard the name Fresnel!

thanks for the game cfitz haven't had such a good laugh in a while!

there are other nice games there too, need to check out...so far i've been shooting penguins into space :lol:
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor, where the Shadows lie
-- JRRT
M.C. Escher - Reptilien
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Postby cfitz on Tue Nov 25, 2003 10:18 am

dodecahedron wrote:damn, it's a LONG time since i heard the name Fresnel!

I always think of lighthouses when I think of Fresnel.

dodecahedron wrote:thanks for the game cfitz haven't had such a good laugh in a while!

Yeah, it's a bit of a hoot for those of us who haven't completely outgrown our boyhood (slightly demented) fascinations...

dodecahedron wrote:there are other nice games there too, need to check out...so far i've been shooting penguins into space :lol:

I also tried that one and found it to be a lot of fun and an interesting challenge. And you can even claim you are getting a physics/mathematics lesson with it! :D

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