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Old 23rd November 2004, 09:58 PM   #1
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Default lcd projector in brazil

hello peolpe.. its very difficult to get informations about it here in brazil, so i need your help

so i have some doubts..

im thinking about using a slide-projector mainly its objective lens, is it possible ? what else can i use as objective lens ?


1 or 2 fresnel lenses ?

what about the focus ? what distance between the lcd and the objective ? ill use a 5.6 inch lcd

thanks people .. sorry for my poor english

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Old 26th November 2004, 03:52 AM   #2
dracul is offline dracul  Brazil
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Hi,

I am also from brasil . Salvador to be exact now.
You cant use a slide projector lens. its made to focus a 35mm image device. You need the triplets offered on lumenlab. All the your looking for is here. All you have to do is search. Or,
..... you can buy the plans from Lumenlab which I heard is a great time saver. Its still only less than R$60 for you.

The real bummer I find here is the import tax. Its 60% on anything and everything that comes in.
Still I prefer importing compared to buying locally. There just isnt the options you have in the usa or china etc.....
But if you know of a place to get triplets and fresnels please post.
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Old 26th November 2004, 04:35 AM   #3
getafix is offline getafix  Philippines
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Have you read this thread:

http://www.diyaudio.com/forums/showt...468#post494468

he used a slide projector on his project
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Old 26th November 2004, 09:45 AM   #4
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Default working with local materials

If you want to use very inexpensive local lenses, you can make a duplet lens from two positive meniscus lenses mounted at each end of a piece of PVC or ABS pipe. With a small LCD and a long throw design, these could work pretty well. ("long throw" means you put the projector at the back of the room, for example a 95 inch diagonal image from 14 feet is long throw.)

Where could you find such lenses? At a local eyeglass-maker, or the place he gets his lenses before cutting them to fit in the frames. These lenses are very inexpensive because they are mass produced. They are sold by their Diopter rating, instead of by their focal length. But there is a simple relationship:

Diopters = 1000 mm / focal length in mm

So a 1 Diopter lens has a focal length of 1000 mm. If you put one of these lenses at each end of a short tube, with the convex sides facing out, then you will get:

effective focal length total = 0.57 * lens focal length

So you will get a lens with an effective focal length around 570 mm. Eyeglass makers keep a range of lenses from 0.25 up to around 4.0 Diopters, so you can make any focal length you need.

But you should try to get the largest diameter round lenses they have. Maybe 70-80 mm.

Here is an example for a 330 mm duplet:

Get two large 1.75 Diopter positive meniscus lenses. (ie. reading glasses). Put one at each end of a tube so the lenses are 5.72 inches apart. It might give you a clearer image with a disk mounted in the middle with a 1.9 inch diameter hole at the center. This would make an f/6 lens. You can also experiment with smaller holes to see if your projected image gets sharper.

You can scale this example up or down for other focal lengths.
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Old 26th November 2004, 10:55 AM   #5
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here in brazil you can find everything in www.mercadolivre.com.br
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Old 26th November 2004, 01:49 PM   #6
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Default ar coating also possible

if ya decide to go with opticians blanks then you have some other options like anti reflection coating ... get the cheapest coating done that will help immensly.
i am right now using one of those 60mm 9diopters lens as my condenser and works great and if you can befriend that dude their machine can grind upto 100 mm lens ... my lens made from anti uv glass is being ground as i type this ...hope this helps

btw anybody know how to assemble a three element lens cause these opticians also have negative power lenses....
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Old 26th November 2004, 06:27 PM   #7
dracul is offline dracul  Brazil
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Quote:
here in brazil you can find everything in www.mercadolivre.com.br
Everythinggggggggggggggggggggggggggggg?

I know about mercadolivre and have been looking for triplets, opaque projectors and lcd kits but never found anything like that.

As far as lcd monitors starting at over $300 usd for used. I understand its more expensive but there just arent any options such as ebay. no dell, no sgi not much of anything really.
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