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Old 19th November 2006, 02:45 PM   #121
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Default Just one more question.

What is the diffrent between the fresnel infront of the LCD and the one behind? Is it just the focal lenght?

Sorry for tripple posting

Mr newbie here.
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Old 20th November 2006, 09:39 AM   #122
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The difference is the focal length. The fresnel between the lamp and the LCD should have a fairly short focal length (like 220 mm). The distance between the lamp arc and the fresnel would then be about 220 mm. If you used a longer focal length fresnel, then it would have to be further from the lamp arc. Then it would collect less light. You need as much light as possible, and a 220 mm fl fresnel is optimal for this.

The fresnel between the LCD and the projection lens must have a focal length that matches the distance between the LCD and the projection lens. You can calculate that distance given the projection lens focal length and the throw distance (lens to screen):

1/x = 1/lens fl - 1/throw (all in mm)

For a throw distance of 3 meters and a projection lens with a 34 cm fl:

1/x = 1/340 - 1/3000
x = 383 mm

The closest fresnel that you can buy is a 330 mm fl.
From 3dlens, you would buy their #F220 and #F330 fresnels.

You already have a 17" LCD, so your choices are limited. But you should also have a look at these:

https://secure.lumenlab.com/shop/group.php?id=15
www.exclusiv-online.com

Your English is very good. Much better than my Swedish (since I have NO Swedish at all.)
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Old 20th November 2006, 02:20 PM   #123
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Ok, i thing im starting to understand what i should have.
Hers the deal: I Buy 2 fresnel lenses from 3dlens.com one 220 mm and one 330 mm. I also buy a lamp (bulb) from lummenlab.com (400w recommeded). Heres the question: Is it accepteble to use a fresnel with a focal length of 330 mm with a projektor lens from lumenlab.com with a focal lenght of 320 mm? It?07s just 10 mm, is that sufficient?

/Thanks guy for taking your time helping me. Much appreciate!
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Old 20th November 2006, 02:20 PM   #124
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oh forgot to ask: Is it nessessary to use a condensor? Or is that just making the quality better?

/Again thanks!
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Old 20th November 2006, 06:20 PM   #125
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It would be better if you could find a fresnel that had a bit longer focal length. You can use the equation I gave earlier to calculate exactly the LCD-to-projector lens distance for your throw distance and any projection lens. For a 320 mm fl lens, that distance will probably be between 340 and 380 mm.

I don't think there is a fresnel available with that focal length. 330 mm is close enough. You can adjust the lamp-to-fresnel distance by a few millimeters to compensate.

If you were building a projector using a 7" or 8" LCD, then a condensor lens would collect more light. With a 17" LCD, it will not make much difference so you should not bother with it. But you should get a good spherical reflector. The DIY projector sites sell them, or you can use the polished aluminum napkin holder from IKEA.
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Old 23rd November 2006, 04:21 PM   #126
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Exclamation Question about anti-glare and fresnels again!

Ok, just started my project. I have buildt a projector box and next to do is to buy some lenses. Today i removed my anti-glare (Polarizer) successfuly (ihope). Then when i did a "check run" on my LCD i discovered that i didnt get any picture! Oh no i thought, now im screwed! Then when i tryed my last hope i could finally breath out. I discovered that something in the anti-glare thing was important. I held my anti-glare infront of the screen and a picture was visible.

Question: is the picture goin to be visible in the projection? Or do i need to buy a new one?

BTW: Looked on a tutorial, but it didnt say something about this issue.

Again sorry for my bad english.

/Thanks!
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Old 18th November 2007, 05:38 PM   #127
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Hmm, A good lesson in polarization. It been a while for me on the diy projection topic, but sounds to me like a polarizing sheet of film off the LCD. This changes the alignment of the light for the human eye to see it. Yes you will need that sheet even when projecting. If the sheet is destroyed there is a cheap trick. 3M gives out free 7X10 samples . Just takes a little research on their site. 3m sells all sorts of cool films that can work great for diy projectors. I bet if you were to wear a nice pair of sunglasses you could see the image just fine.
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Old 19th November 2007, 12:39 AM   #128
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Polarization is how the LCD works: Light enters the glass sandwich with one polarity (from the first polarization filter). The liguid crystal twists the polarity to some extent. (The amount of twist depends on the charge across the liquid crystal in each cell.) When the light leaves the glass sandwich it strikes another polarization filter. If the light's polarity matches the second filter, then it passes. If it is 90 degrees off, then it mostly gets absorbed. Values in between give the different shades.

You need that second filter, but it doesn't have to be right against the glass like the original was. I think you could just put a polarization filter on the projection lens. (You would have to rotate it until the contrast is maximal.) Or you could even project the unfiltered light onto your screen, but view it through polarized glasses. That would be pretty cool because it would look just like a bright white screen to everybody without the "viewing glasses"!

You could even project two different images on the screen at the same time. One projector would use a second filter polarized in the verticle direction, and the other in the horizontal direction. Use the horizontal glasses to see one image, the verticle glasses to see the other. This is the basis of color 3-D projection.

Try some experiments. Have some fun.
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Old 29th November 2007, 10:43 PM   #129
nzshy is offline nzshy  Canada
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Default For newbies post #27

Great info, thanks tones. After reading everything till my eyes bulged out of my head...he he he. I put together a projection system; here it is,

overhead= DA-Lite 5000 also used an Elmo HP4K by Dukane 4000
LCD Panel= Nview Z115
screen= home made 72" x 112"
Sanyo Home theater DVD 5.1 player


WOW! WOW! WOW! my family thinks it's great, and my kids now play the PS2 games on it. Thanks to all here for educating me to the point
where I could do this. Please keep up the great work.
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Old 30th November 2007, 03:34 AM   #130
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Default Re: Things Newbies Should Know

Quote:
Originally posted by verbose mustafa
[B]
LEDS Will not work (yet)

This video forum was started on the basis of using leds as a light source. It did not work... leds are not bright enough at all.
Ok, I was just browsing around this thread, and I think you may be able to use LED's....

Later on you state that 4000 lumens is a good figure, and cree XR-E leds are 100 lumens each.

If you had 40 x XR-E leds, each with thier own optics/reflectors, then 4000 lumens from led's might be possible...

It would be expensive and fiddly, but it just might work!
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