hrmm..
Hellfire,
Thats a fantastic Idea. I've been researching it as much as I could the past few hours. What I found is..porthole glass is really hard to find. if you could find it, you'd be lucky to find a slab of it that was 1" thick -- and after a ton of time and effort grinding and smoothing it down, the curve just wouldn't be deep enough to get an acceptable focal length. you'd end up with a 12-16" diameter with a curvature of f5 or above -- which means 60" or more focal length. I don't want my projector to be more than five feet long :\
So, unfortunately, I think thats out of the picture, along with expensive telescope parabolic mirrors.
I'm really wondering if there is some way...that you could take one of those aluminum parabolic reflectors, and coat the inside of it with something better than plain polished aluminum. Does anyone have any ideas about that?
Hellfire,
Thats a fantastic Idea. I've been researching it as much as I could the past few hours. What I found is..porthole glass is really hard to find. if you could find it, you'd be lucky to find a slab of it that was 1" thick -- and after a ton of time and effort grinding and smoothing it down, the curve just wouldn't be deep enough to get an acceptable focal length. you'd end up with a 12-16" diameter with a curvature of f5 or above -- which means 60" or more focal length. I don't want my projector to be more than five feet long :\
So, unfortunately, I think thats out of the picture, along with expensive telescope parabolic mirrors.
I'm really wondering if there is some way...that you could take one of those aluminum parabolic reflectors, and coat the inside of it with something better than plain polished aluminum. Does anyone have any ideas about that?
LOA + OHP = crap
well, i used an LOA inside a standard OHP like i said, and no such luck... these babies have a TON of light, but its just not focused enough. i was kinda hoping enough would just get through to work, but it didnt. im going to experiment some more, and see if i can find a way to focus this light, and possibly attach it to the bottom of the projector.
if there was a way to focus and concentrate the light that comes out of this thing, i definately think it would work. anyone have any ideas?
well, i used an LOA inside a standard OHP like i said, and no such luck... these babies have a TON of light, but its just not focused enough. i was kinda hoping enough would just get through to work, but it didnt. im going to experiment some more, and see if i can find a way to focus this light, and possibly attach it to the bottom of the projector.
if there was a way to focus and concentrate the light that comes out of this thing, i definately think it would work. anyone have any ideas?
search for a parabolic mirror
Well, after giving this much effort, I have come up nearly empty handed. I started broadening my search to include spherical mirrors and other convex mirrors. The result of a spherical mirror will be slightly less accurate and precise as a parabolic mirror, but, since the optical lens collecting the light is going to have a few inches diameter, a precise focal point reflection probably wouldn't be needed.
So, my best bet would be this:
40cm Convex Mirror
MIRROR - SPHERICL 40CM/CONCAVE
Catalog Number(s): WL3525A
Description: EAGLE CONVEX GLASS CO SE, WL3525A.
made by Eagle glass Co.
Thats about 15 3/4" diameter -- plenty big enough
it doesnt give the distance of the focal point, but, you would easily be able to find it by getting out a flaslight, pointing it at it, and taking a piece of paper and moving it back and forth until you see when the light is converged the closest. Designing the LED panel using a spherical convex mirror means that packing as many LED's across from the mirror as close to the Center of the mirror as possible would yield the best results, and as you added LEDs further and further out on the diameter of the mirror, they would be less accurate and stray slightly from the focal point. If I positioned the capturing lens slightly inside of the focal point, I don't think this would be a major problem. we would still be getting well over 95% of the light that is being reflected from the mirror.
If Vince is still around here, I'd like to know if he thinks these LEDs are bright enough. Its just a lot of money to throw around (well, maybe not a lot if I didnt have a family to support). Wish I could borrow the stuff to test it out before I made any purchases 🙂
I'll post some more sketches soon.
Well, after giving this much effort, I have come up nearly empty handed. I started broadening my search to include spherical mirrors and other convex mirrors. The result of a spherical mirror will be slightly less accurate and precise as a parabolic mirror, but, since the optical lens collecting the light is going to have a few inches diameter, a precise focal point reflection probably wouldn't be needed.
So, my best bet would be this:
40cm Convex Mirror
MIRROR - SPHERICL 40CM/CONCAVE
Catalog Number(s): WL3525A
Description: EAGLE CONVEX GLASS CO SE, WL3525A.
made by Eagle glass Co.
Thats about 15 3/4" diameter -- plenty big enough
it doesnt give the distance of the focal point, but, you would easily be able to find it by getting out a flaslight, pointing it at it, and taking a piece of paper and moving it back and forth until you see when the light is converged the closest. Designing the LED panel using a spherical convex mirror means that packing as many LED's across from the mirror as close to the Center of the mirror as possible would yield the best results, and as you added LEDs further and further out on the diameter of the mirror, they would be less accurate and stray slightly from the focal point. If I positioned the capturing lens slightly inside of the focal point, I don't think this would be a major problem. we would still be getting well over 95% of the light that is being reflected from the mirror.
If Vince is still around here, I'd like to know if he thinks these LEDs are bright enough. Its just a lot of money to throw around (well, maybe not a lot if I didnt have a family to support). Wish I could borrow the stuff to test it out before I made any purchases 🙂
I'll post some more sketches soon.
Parabolic mirror
Undream and everyone else
Do not forget that a parabolic mirror can olso be used with other lightsources like LOA and others.
Underbeam, You hit the neil with this one 🙂
But I think that You realy need a point source as small as posible and from that spred the light out in a correct manner to get a sharp picture . . . . . . . or do You?
Bye for now
Undream and everyone else
Do not forget that a parabolic mirror can olso be used with other lightsources like LOA and others.
Underbeam, You hit the neil with this one 🙂
But I think that You realy need a point source as small as posible and from that spred the light out in a correct manner to get a sharp picture . . . . . . . or do You?
Bye for now
Gunawan
Thanks for your input! I think I understand what you are doing...are you basically using two plano-convex lenses: one with short focal length for "reducing" the LCD image and then one with a long focal length for projection? That would make sense, I think. I have tried using a double convex lens, with the same focal length for both sides, but I am getting a very blurry projected image, espcially around the edges. I have heard that an achromat lens can correct for distortion around the edges. Would this correction be necessary when using two plano-convex lenses of different focal length? I'm probably asking too much...maybe I'll just try it out. Thanks again for the tip.
Question about the parabolic reflector: Once the light has been condensed to a point, it must diverge again enough to illuminate the LCD. Wouldn't the light be scattered again, defeating the purpose of condensing the light to a point? In other words, wouldn't this be the same thing as passing a light through a lens? I'm not trying to kill the idea, because I think it sounds great. But I'm just trying to see the real benefit of doing this.
Good luck everyone!
-f4
Thanks for your input! I think I understand what you are doing...are you basically using two plano-convex lenses: one with short focal length for "reducing" the LCD image and then one with a long focal length for projection? That would make sense, I think. I have tried using a double convex lens, with the same focal length for both sides, but I am getting a very blurry projected image, espcially around the edges. I have heard that an achromat lens can correct for distortion around the edges. Would this correction be necessary when using two plano-convex lenses of different focal length? I'm probably asking too much...maybe I'll just try it out. Thanks again for the tip.
Question about the parabolic reflector: Once the light has been condensed to a point, it must diverge again enough to illuminate the LCD. Wouldn't the light be scattered again, defeating the purpose of condensing the light to a point? In other words, wouldn't this be the same thing as passing a light through a lens? I'm not trying to kill the idea, because I think it sounds great. But I'm just trying to see the real benefit of doing this.
Good luck everyone!
-f4
cowanrg, this LOA is nothing else than a very bright backlight ! Its unpossible to focus it properly through the LCD to projection lens. I think you have even better results without the fresnel. Large sized light sources are never a good choice for projection, because they are hard to handle from optical point of view.
If you look at MH lamps or halogen types, ALL the power is produced within a small area of a few sq mm! This is where parabolic mirrors and fresnels make sense. A LOA is a huge light source and diffuser too. Every point on the bulbs surface is a little, but not so bright lightsource, which is emitting light into all directions.
The same with these LED arrays.
xblocker
If you look at MH lamps or halogen types, ALL the power is produced within a small area of a few sq mm! This is where parabolic mirrors and fresnels make sense. A LOA is a huge light source and diffuser too. Every point on the bulbs surface is a little, but not so bright lightsource, which is emitting light into all directions.
The same with these LED arrays.
xblocker
Point light sources
Underdream: Ages ago we decided that LEDs are too expensive and don't give out a lot of light. In fact, LEDs actually give out LESS light per £ or even per square inch than other sources, such as fluorescent lights.
I've been reading about this point light source thing with little interest (I'm not doing LCD as everyone knows) for quite a while. I think there could still be some confusion with it, so here is my understanding of it for you to correct if I'm wrong...
If you're using a fresnel, as in an OHP, then you want a point light source. This is because the fresnel takes the point light source and turns it into a nice parallel beam of light. If you don't use a point light source with a fresnel, then all of the light that isn't being produced at the focus of the fresnel, is going to be bounced around in all kinds of directions, which isn't going to be efficient and certainly won't produce a good quality result.
Fresnel -> Point light source
Not-Fresnel -> Bigger light source, although polarisers would apparently be good so that the light travels through the LCD in parallel. Nobody seems to know much about polarisers.
Yes you need fresnels in an OHP, because the light goes from a point source to a parallel beam and then back to a converging beam, through a big LCD panel, and into some nice quality optics at the end of a big arm, before being focused onto the wall.
Also, I've seen something in a lot of people's diagrams over the many pages of this forum. You do realise that if you're going to have a lens to project the image, you can't have the image source greater than the size of the lens, because that would require something we haven't harnessed yet: Magic.
Underdream: Ages ago we decided that LEDs are too expensive and don't give out a lot of light. In fact, LEDs actually give out LESS light per £ or even per square inch than other sources, such as fluorescent lights.
I've been reading about this point light source thing with little interest (I'm not doing LCD as everyone knows) for quite a while. I think there could still be some confusion with it, so here is my understanding of it for you to correct if I'm wrong...
If you're using a fresnel, as in an OHP, then you want a point light source. This is because the fresnel takes the point light source and turns it into a nice parallel beam of light. If you don't use a point light source with a fresnel, then all of the light that isn't being produced at the focus of the fresnel, is going to be bounced around in all kinds of directions, which isn't going to be efficient and certainly won't produce a good quality result.
Fresnel -> Point light source
Not-Fresnel -> Bigger light source, although polarisers would apparently be good so that the light travels through the LCD in parallel. Nobody seems to know much about polarisers.
Yes you need fresnels in an OHP, because the light goes from a point source to a parallel beam and then back to a converging beam, through a big LCD panel, and into some nice quality optics at the end of a big arm, before being focused onto the wall.
Also, I've seen something in a lot of people's diagrams over the many pages of this forum. You do realise that if you're going to have a lens to project the image, you can't have the image source greater than the size of the lens, because that would require something we haven't harnessed yet: Magic.
Good points, Scot_lad...we need you back on the LCD side! I wish you the best with the CRT project. It is very interesting.
One question, though. If the projection lens must be larger than the source, then how do OHP's get away with using a lens that is probably 4X smaller than the source? Is this the work of the fresnel before the LCD or a convex lens in the "head"?
-f4
One question, though. If the projection lens must be larger than the source, then how do OHP's get away with using a lens that is probably 4X smaller than the source? Is this the work of the fresnel before the LCD or a convex lens in the "head"?
-f4
To avoid confusion about all this lenses: In reality we have two (!) image systems! One is the light source projected right into the projection lens's plane. This is the lighting path. The other is the image path going from LCD through projection lens to the screen.
The size of projection lens doesn't depend of the size of the LCD panel. It only depends of the speed (american term?) and focal length of the lens.
If the light source isn't so bright (CRT), the speed must be better, that's why CRT lenses have to be larger. Similar conditions as in photography.
In the case of an OHP this isn't so important, because the LCD's image is concentrated through the illumination path. Important is only, that focus lenght > object (LCD diagonal)!
Hard to explain...
xblocker
The size of projection lens doesn't depend of the size of the LCD panel. It only depends of the speed (american term?) and focal length of the lens.
If the light source isn't so bright (CRT), the speed must be better, that's why CRT lenses have to be larger. Similar conditions as in photography.
In the case of an OHP this isn't so important, because the LCD's image is concentrated through the illumination path. Important is only, that focus lenght > object (LCD diagonal)!
Hard to explain...
xblocker
thanks for input
This is exactly what I was looking for, was someone to tell me it wont work, because, I think I was getting ahead of myself. I need to read up on many more things. I really didn't know what I was talking about beyond the light source, thats what I was really concerned about. I figured I would figure out the rest later. I liked the idea of LEDs, and was trying to think of a way to take many, many of them and converging the light to one point. I would gladly spend $150 on them as a light source, over a $40 halogen or something. I didnt want to have to deal with heat, fans, cold mirrors, and replacing bulbs. I thought over time, they would be much much less expensive If you have to replace another light source 5, 6 or 7 times to match the life of a LED?
This is exactly what I was looking for, was someone to tell me it wont work, because, I think I was getting ahead of myself. I need to read up on many more things. I really didn't know what I was talking about beyond the light source, thats what I was really concerned about. I figured I would figure out the rest later. I liked the idea of LEDs, and was trying to think of a way to take many, many of them and converging the light to one point. I would gladly spend $150 on them as a light source, over a $40 halogen or something. I didnt want to have to deal with heat, fans, cold mirrors, and replacing bulbs. I thought over time, they would be much much less expensive If you have to replace another light source 5, 6 or 7 times to match the life of a LED?
lenses?
Two quick questions.
What direction should the fresnel be when its before the lcd?
What projection lense would anyone recomend for my final projection lense (I'm using a 4" lcd)?
Two quick questions.
What direction should the fresnel be when its before the lcd?
What projection lense would anyone recomend for my final projection lense (I'm using a 4" lcd)?
FYI
Hey, I just found out a way to search this thread (since the search on DIYaudio doesn't do much good for searching within a thread). At the bottom of the page, there is a "Show Printable Version" link that will take you to a page with all of the posts show at once! Then you can use the Ctrl-F or Find function to search for keywords, topics, parts, etc. Maybe everybody already knew that, but I sure didn't. It would have save me a good bit of time seraching for things. Hope this helps.
wnichols,
For you purpose, I would recommend the Fujinon lens from Surplus Shed. According to the description, it will accomodate a source up to 4.25", so you may be in business. I have one, and it does seem to be a hih quality item. Good luck with it.
-f4
Hey, I just found out a way to search this thread (since the search on DIYaudio doesn't do much good for searching within a thread). At the bottom of the page, there is a "Show Printable Version" link that will take you to a page with all of the posts show at once! Then you can use the Ctrl-F or Find function to search for keywords, topics, parts, etc. Maybe everybody already knew that, but I sure didn't. It would have save me a good bit of time seraching for things. Hope this helps.
wnichols,
For you purpose, I would recommend the Fujinon lens from Surplus Shed. According to the description, it will accomodate a source up to 4.25", so you may be in business. I have one, and it does seem to be a hih quality item. Good luck with it.
-f4
VG140 Problem??
It may be just me, but I'm not understanding jjasniew's problem with the vg140, with the last picture it shows the panel with the circuit boards completly out of the way of everything... Am I missing something... Which connecter is the problem?
So anyways, jjiasniew (or anyone) have you solved the problem, is the vg140 board workable for our needs?
It may be just me, but I'm not understanding jjasniew's problem with the vg140, with the last picture it shows the panel with the circuit boards completly out of the way of everything... Am I missing something... Which connecter is the problem?
So anyways, jjiasniew (or anyone) have you solved the problem, is the vg140 board workable for our needs?
Attachments
prices
ever since i began reading this board and looking at the ovation lcd monitors on ebay, the prices seem to be going up and up...are we all bidding against each other??? what seems to be a reasonable price to pay for a 820?
ever since i began reading this board and looking at the ovation lcd monitors on ebay, the prices seem to be going up and up...are we all bidding against each other??? what seems to be a reasonable price to pay for a 820?
OHP lenses - correct me if I'm wrong
Just to mop up a wee question: OHPs have a much smaller lens than the size of the image source, because the light beams converge towards the smaller lens. This is achieved because of the fresnel arrangement between the light source and the LCD panel.
As for image 'speed', sorry I've not idea at all what that means, XBlocker, maybe you could explain for the non-US guys?
I am looking forward to watching my latest DVD on some kind of projection system: does anyone remember Jamie and the Magic Torch?
www.80snostalgia.com will provide a nice distraction from projector panels and lenses... 🙂
Just to mop up a wee question: OHPs have a much smaller lens than the size of the image source, because the light beams converge towards the smaller lens. This is achieved because of the fresnel arrangement between the light source and the LCD panel.
As for image 'speed', sorry I've not idea at all what that means, XBlocker, maybe you could explain for the non-US guys?
I am looking forward to watching my latest DVD on some kind of projection system: does anyone remember Jamie and the Magic Torch?
www.80snostalgia.com will provide a nice distraction from projector panels and lenses... 🙂
Scot_lad
I asume that by speed, Xblocker is refering to the aperture of the lens, allowing more light through and thus (for a camera system) allowing a shorter or faster exposure.
As For Jamie and the magic torch, I never really liked it, Will 'o' the wisp was more fun.
Nick.
I've no money at the moment, grrrrrr. Experimenting over...
I asume that by speed, Xblocker is refering to the aperture of the lens, allowing more light through and thus (for a camera system) allowing a shorter or faster exposure.
As For Jamie and the magic torch, I never really liked it, Will 'o' the wisp was more fun.
Nick.
I've no money at the moment, grrrrrr. Experimenting over...
fender4
Try reversing the Fujinon lens. Normally you have to place the object very close to it to project a good image; I have observed that by reversing the lens you can increase the object distance and therefore easily cover a much bigger object. The wide angle attribute of the lens is still preserved.
Try reversing the Fujinon lens. Normally you have to place the object very close to it to project a good image; I have observed that by reversing the lens you can increase the object distance and therefore easily cover a much bigger object. The wide angle attribute of the lens is still preserved.
Thanks or the tip, lokost. I've tried it, and unfortunately, I am still missing about 30% of the image. I have ordered a plano-convex lens that has a focal length of ~12" (the same one that Gunawan recommended), so hopefully I can use that to "gather" the image and send it to the Fujinon. I think I am being limited by the short focal length of the Fujinon.
-f4
-f4
contrapasta
You have outlined the problem precisely. I have not yet checked them out, to see if they'd mail overseas.
In your second photo, the connector is just underneath the edge of the PCB where your arrow points. I believe their solution will work; it's just a matter of getting it.
You have outlined the problem precisely. I have not yet checked them out, to see if they'd mail overseas.
In your second photo, the connector is just underneath the edge of the PCB where your arrow points. I believe their solution will work; it's just a matter of getting it.
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