I am trying to build an enclosure for my project. I am dismantling my 3M 9700 and removing the fresnel lens. Does anyone know or know how to find out the focal length on this lens? It's actually 2 lenses sandwiched together. I looked up a .pdf for it from 3Mand it said the Fresnel is 182.5mm (only list one size). The triplet lens is 342mm.
Does that mean one side has 182.5mm and the other is 342mm?
Thanks in advance
Slappy
BTW. After dismantling my NEC 1545v I am getting a line (2-3 pixels thick) across the botton 10% of the screen (no biggie). I'll look at the flex cable on the LCD with a loupe but I don't think I'll be able to do much even if I locate the problem. I gotta be even more gentle dismantling these things.
Does that mean one side has 182.5mm and the other is 342mm?
Thanks in advance
Slappy
BTW. After dismantling my NEC 1545v I am getting a line (2-3 pixels thick) across the botton 10% of the screen (no biggie). I'll look at the flex cable on the LCD with a loupe but I don't think I'll be able to do much even if I locate the problem. I gotta be even more gentle dismantling these things.
I think the 182.5mm FL refers to the effective focal length, which takes into consideration both fresnels focal length. Mine, for example is 125.5mm EFL, and the focal lengths separatedly were 182mm and 406mm.
As for testing it, I would suggest to try mid-day sunlight and measure the distances of the light point it produces to the fresnel, on each side. Not sure it would work perfectly, when I did that with a regular bulb I found similar measures to what I found in the specifications of the lens.
As for testing it, I would suggest to try mid-day sunlight and measure the distances of the light point it produces to the fresnel, on each side. Not sure it would work perfectly, when I did that with a regular bulb I found similar measures to what I found in the specifications of the lens.
Is there a thread around here that discuses how you know which fresnel to buy? It seems that everybody magically knows what focal length to get w/ their projectors when choosing their fresnel -_-' Some look like they require some distance from the lcd, while others are sticking it onto the back of the lcd panel... Is it just pick one and figure it out through messin around?
There are calculators like these:
http://www.diyprojectorcompany.com/theory/calculator.htm
Knowing any of the 3 things will yield the 4th:
For example:
1) Where do you want to place the projector? (distance to wall/screen)
2) The size of your LCD panel. (10", 15", 17". etc)
3) The size of the projected image.
4) Will determine the Projection lens FL
(your fresnel should closely match the projection lens as close as possible)
So in my case..
I have a 3m 9700 projector with a 342mm FL triplet lens
I have a 15in panel
I am placing the projector 8 feet away (96 inches)
The calculator says the image will be about 91 inches.
I also have a spare 100mm FL lens (assuming I had a matching 100mm Fresnel) but that wouldn't work because the projected image would be 342inches. Too big and too dim. My LCD would have to be 4-5 inches for me to use this 100mm FL lens.
http://www.diyprojectorcompany.com/theory/calculator.htm
Knowing any of the 3 things will yield the 4th:
For example:
1) Where do you want to place the projector? (distance to wall/screen)
2) The size of your LCD panel. (10", 15", 17". etc)
3) The size of the projected image.
4) Will determine the Projection lens FL
(your fresnel should closely match the projection lens as close as possible)
So in my case..
I have a 3m 9700 projector with a 342mm FL triplet lens
I have a 15in panel
I am placing the projector 8 feet away (96 inches)
The calculator says the image will be about 91 inches.
I also have a spare 100mm FL lens (assuming I had a matching 100mm Fresnel) but that wouldn't work because the projected image would be 342inches. Too big and too dim. My LCD would have to be 4-5 inches for me to use this 100mm FL lens.
sh!t I cracked my sandwiched fresnel lens! Grr.. it's not too bad. It only extends a tiny bit to the LCD field.
Okay.. the plastics used on the lens are really REALLY brittle and you cannot use any significant force. Keep running a utility blade thru as many times as you can to split it. No prying with a screwdriver! Nuts!
Okay.. the plastics used on the lens are really REALLY brittle and you cannot use any significant force. Keep running a utility blade thru as many times as you can to split it. No prying with a screwdriver! Nuts!
I cracked up mine when I was splitting it up too. And i used a knife! No screwdriver watsoever. Atleast it was to be disposed anyway, it was too deformed and marked with heat, I could never look at the projection again without being disgusted.
Next time I will use the most thin blade i can find, maybe even those shaving blades.
Next time I will use the most thin blade i can find, maybe even those shaving blades.
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