keystone
I think that the best way to do keystone correction is with a mirror.
flip your lcd around to reverse the image then use a mirror to flip it back. By changing the angle of the mirror you can change the keystone factor.
If the light path from the projector is square with the screen in the reflected image then there will be no keystone effect.
btw
the mirror should be after the optics 🙂
I think that the best way to do keystone correction is with a mirror.
flip your lcd around to reverse the image then use a mirror to flip it back. By changing the angle of the mirror you can change the keystone factor.
If the light path from the projector is square with the screen in the reflected image then there will be no keystone effect.
btw
the mirror should be after the optics 🙂
Hi there everyone. You can count me as one of the countless people who's been following this thread and hasn't contributed yet. I noticed there's been some talk of building a reflector. I was wondering if anyone has looked into aluminized mylar for a reflective surface. It's dirt cheap, and the good quality stuff has over 90% reflection. I was interested in building a solar concentrator at one time, and builders use aluminized mylar to produce a mirror-like finish on a parabolic surface. It would take some practice to put on properly, but the end result should work quite well. Also, I'm very interested in mountain_nz's idea. It sounds great. Also hoping not everyone has given up hope on the CRT idea? I think for a really good quality hi-res image, CRT would be just about the only way to go. I found this thread after looking for a way to display the video from my newly purchased HDTV tuner set top box. I plugged it in to an ancient old 14" computer monitor and the picture is absolutely jaw dropping. It makes me want to look into crt-based ideas... The scan rate for 1080i HDTV is ~33.75khZ. That's not a huge leap from mountain_nz's NTSC based ~15khz... (Sorry, I'm nowhere near an expert on display systems). I'm willing to crack open this 14" monitor and start playing around. 🙂
Mountain,
as far as i understand your construction, it is similar to laserprojector concept. But the lighting design can't work! It's unpossible to couple a focused LED light cone into a fibre pipeline and get out a parallel lightbeam. Even if you would focus the sun into it...! Also the light emitting LEDs don't produce parallel light. Most of the LEDs light is wasted and doesn't reach the fibre's aperture. Make a ray traycing and you see it. This is only possible with laser light and momo mode fibre optics, as far as i know.
Look at this:
as far as i understand your construction, it is similar to laserprojector concept. But the lighting design can't work! It's unpossible to couple a focused LED light cone into a fibre pipeline and get out a parallel lightbeam. Even if you would focus the sun into it...! Also the light emitting LEDs don't produce parallel light. Most of the LEDs light is wasted and doesn't reach the fibre's aperture. Make a ray traycing and you see it. This is only possible with laser light and momo mode fibre optics, as far as i know.
Look at this:
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Almost forgot, for those interested in LCD projection:
If you want to open up a LCD monitor, a good choice might be the 15" model from Solarism. It has a 25ms response rate, which virtually eliminates blurring from the LCD. It's got S-video and composite inputs as well. Although it's a little pricey (I think around $500). It also has the brightest backlight on the market, even though it wouldn't really be useable in a projection system.
If you want to open up a LCD monitor, a good choice might be the 15" model from Solarism. It has a 25ms response rate, which virtually eliminates blurring from the LCD. It's got S-video and composite inputs as well. Although it's a little pricey (I think around $500). It also has the brightest backlight on the market, even though it wouldn't really be useable in a projection system.
xblocker
It is possible to do it. you can use a focusing lense to bring the image down to the size of the fiber then use a micro pcx lens to make the light ray parallel. then it would have laser like properties.
It is possible to do it. you can use a focusing lense to bring the image down to the size of the fiber then use a micro pcx lens to make the light ray parallel. then it would have laser like properties.
oftheend...thats great to hear about the light.
Is the bulb really large like the MV bulbs? Does it have one of those STUPID "eyes" at the top?
what about light distribution, are you getting any bright spots?
Is your new light setup basically the same as before (i.e. taken from a dusk-to-dawn light) or did you order from elsewhere?
I was looking at my stuff last night (which I havent touched for 2 weeks) and I realized that I have probably been taking the wrong approach with my light. I have been pointing my light at the fresnel. I think a lot of the light gets defracted away from the freslen because of the sharp angles at the tip of the light and the "eye" thing at the tip. I wan to try standing the light up and see if I get better results....It's hard for me to explain and those that havent seen the MV lights probably have no idea what I'm talking about. I am pretty sure oftheend will because I want to try placing my light the way he has his (you can see a picture or link to his about 10 pages back or so...and a picture of mine is attached below.
Is the bulb really large like the MV bulbs? Does it have one of those STUPID "eyes" at the top?
what about light distribution, are you getting any bright spots?
Is your new light setup basically the same as before (i.e. taken from a dusk-to-dawn light) or did you order from elsewhere?
I was looking at my stuff last night (which I havent touched for 2 weeks) and I realized that I have probably been taking the wrong approach with my light. I have been pointing my light at the fresnel. I think a lot of the light gets defracted away from the freslen because of the sharp angles at the tip of the light and the "eye" thing at the tip. I wan to try standing the light up and see if I get better results....It's hard for me to explain and those that havent seen the MV lights probably have no idea what I'm talking about. I am pretty sure oftheend will because I want to try placing my light the way he has his (you can see a picture or link to his about 10 pages back or so...and a picture of mine is attached below.
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new reflector
I will be working on a new reflector this weekend. Thanks to some tips from tech_head on creating my mold, I hope I can at least build a fiberglass reflector this weekend (although I know I wont have time by then to get it electroplated).
I will be making an elipsoidal reflector...but I think I would also like to make a parabolic reflector. Here is my reaoning...please tell me if I'm wrong...
A complet parabola will reflect all the light from one focus to the other. We know this and that has been the hype about building ellipsoidal reflectors. Howevers, the light does not just all head over that way....a lot of light needs to bounce off the reflector on the destination side...since we are only using the source half of the ellipse, and ideally placing just an LCD there, we be losing a good chunck of light This is beacuse the light that has not been reflected off our reflector (the light that starts off directed away from the reflector) is expected to bounce of the other side of the ellipse in order to properly reach the focus....This is why I am going to use a Fresnel still even though I am using an ellipsoidal reflector. If I throw my fresnels right at the end of the reflector I will get almost ALL of the light that is being emitted from my bulb (assuming I have a highly reflective surface). The fresnel can then focus the light throught the LCD and down to my projection lens.
The only reason I was thinking of a parabolic reflector is so I can send the light out in parallel and hope it gathers more light...I could also possible remove the first fresnel if I had parallel rays soming in.
I hope this makes sense...please let me know what you think...I will try to draw some pictures to show what I mean.
Later,
Dave
I will be working on a new reflector this weekend. Thanks to some tips from tech_head on creating my mold, I hope I can at least build a fiberglass reflector this weekend (although I know I wont have time by then to get it electroplated).
I will be making an elipsoidal reflector...but I think I would also like to make a parabolic reflector. Here is my reaoning...please tell me if I'm wrong...
A complet parabola will reflect all the light from one focus to the other. We know this and that has been the hype about building ellipsoidal reflectors. Howevers, the light does not just all head over that way....a lot of light needs to bounce off the reflector on the destination side...since we are only using the source half of the ellipse, and ideally placing just an LCD there, we be losing a good chunck of light This is beacuse the light that has not been reflected off our reflector (the light that starts off directed away from the reflector) is expected to bounce of the other side of the ellipse in order to properly reach the focus....This is why I am going to use a Fresnel still even though I am using an ellipsoidal reflector. If I throw my fresnels right at the end of the reflector I will get almost ALL of the light that is being emitted from my bulb (assuming I have a highly reflective surface). The fresnel can then focus the light throught the LCD and down to my projection lens.
The only reason I was thinking of a parabolic reflector is so I can send the light out in parallel and hope it gathers more light...I could also possible remove the first fresnel if I had parallel rays soming in.
I hope this makes sense...please let me know what you think...I will try to draw some pictures to show what I mean.
Later,
Dave
superdave,
what lens are you using for projection? Also, have you tried to cover the light source so everyting is light tight expect for the lcd? Like a box over the light so the only light that comes out is from the lcd.
what lens are you using for projection? Also, have you tried to cover the light source so everyting is light tight expect for the lcd? Like a box over the light so the only light that comes out is from the lcd.
DPW666...right now I am just using the lens I took from my ELMO OHP. Its nothing special but it works. I am using the fresnels from it too...so I have a section of my screen cropped out.
Also...yes I have enclosed it so barely any light escapes but I still am not getting much light output through the fresnels...You have to remember that I just bought a metal bowl and hoped that would help (unfortunaletly it didnt and now I have a bowl with a hole).
You can look at my webpage and see pictures of my funky-box-case.
http://www.csun.edu/~hbpsy028/projector/temp/Image025.jpg
Also...yes I have enclosed it so barely any light escapes but I still am not getting much light output through the fresnels...You have to remember that I just bought a metal bowl and hoped that would help (unfortunaletly it didnt and now I have a bowl with a hole).
You can look at my webpage and see pictures of my funky-box-case.
http://www.csun.edu/~hbpsy028/projector/temp/Image025.jpg
drawings
OK...the 3 pictures below detail why I think the fresnels are still needed.
the first drawing shows the light path of an entire elliptical reflector...
the second show how we lost a good portion of light if we only use a reflector and LCD...it has been suggested a number of times that fresnels will not be neede. Although the are not necessary we will get more use of our light if we use them.
the third show how the use of fresnels will make use of almost all light produced from our bulb.
OK...the 3 pictures below detail why I think the fresnels are still needed.
the first drawing shows the light path of an entire elliptical reflector...
the second show how we lost a good portion of light if we only use a reflector and LCD...it has been suggested a number of times that fresnels will not be neede. Although the are not necessary we will get more use of our light if we use them.
the third show how the use of fresnels will make use of almost all light produced from our bulb.
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jjasniew
How much did you say you were selling your OHP for? And roughly how much would it cost to post it to Britain?
How much did you say you were selling your OHP for? And roughly how much would it cost to post it to Britain?
SuperD,
I am with you on the problem caused by the non-reflected light coming directly from the bulb, but won't the fresnel refract the reflected light and negate the advantage of using an ellipse in the first place? I hope that makes sense.
If you wanted to eliminate scattered light caused by the non-reflected light, you could try this:
Parabolic Polarizing
reflector---> sheet------>fresnel--->LCD--->lens
Remember that OHP fresnels are actually TWO fresnel lenses---one to make diverging rays parallel and one to make the parallel rays converge. In this case, you would need a frensel like a page magnifier (but hopefully higher quality). I don't know of a good way to get the non-reflected AND the reflected light to travel uniformly---I'll think about it.
Good luck with the reflector! I'm at a loss for good ideas on that...I'm still playing with aluminum foil. 😎
Question about the LED/laser projector:
First off, pardon my ignorance. Is the LED/fiber optic approach possible because the image is formed before the light has a chance to spread? And then it is projected using a lens? If so, would a smaller, pre-projected image equal a better projected image because of less "dispersion distortion"? Also, would using a higher frequency piezo produce a smaller pre-projected image, although with higher resolution? OK, I'm giving myself a headache. 🙁
Later,
f4
I am with you on the problem caused by the non-reflected light coming directly from the bulb, but won't the fresnel refract the reflected light and negate the advantage of using an ellipse in the first place? I hope that makes sense.
If you wanted to eliminate scattered light caused by the non-reflected light, you could try this:
Parabolic Polarizing
reflector---> sheet------>fresnel--->LCD--->lens
Remember that OHP fresnels are actually TWO fresnel lenses---one to make diverging rays parallel and one to make the parallel rays converge. In this case, you would need a frensel like a page magnifier (but hopefully higher quality). I don't know of a good way to get the non-reflected AND the reflected light to travel uniformly---I'll think about it.
Good luck with the reflector! I'm at a loss for good ideas on that...I'm still playing with aluminum foil. 😎
Question about the LED/laser projector:
First off, pardon my ignorance. Is the LED/fiber optic approach possible because the image is formed before the light has a chance to spread? And then it is projected using a lens? If so, would a smaller, pre-projected image equal a better projected image because of less "dispersion distortion"? Also, would using a higher frequency piezo produce a smaller pre-projected image, although with higher resolution? OK, I'm giving myself a headache. 🙁
Later,
f4
you cant focus both the reflected light and the direct light. you would have to block the direct light or reflect it back to the primary reflector.( lots of reflecting )
that is wyo most of the bulbs that you see in cars have the front of the bulb blacked.
that is wyo most of the bulbs that you see in cars have the front of the bulb blacked.
this might be handy
http://patft.uspto.gov/netahtml/search-bool.html
its the us patent search ... do a search for lcd projectors and find out just what everyone uses?
http://patft.uspto.gov/netahtml/search-bool.html
its the us patent search ... do a search for lcd projectors and find out just what everyone uses?
You cannot focus a large size light sorce such as an led into a small size light source. The source can never be smaller than its original size. You can extract a small portion of a source but you loose the amount of light depending on the ratio of how small you extract compared to original size. This law of optics is in every optics text book is why it is impossible to get enough light from an led into a fibre optic to do any good. Basically you cannot turn a large light source into a small light source without loosing light otherwise they would not need to make short arc lamps.
If there's no way to efficiently get LED light into the fiber, would a laser be the only other alternative? I'm thinking it would be rather difficult to obtain red, green, and blue lasers. Red would be easy enough, green is just more expensive, and I don't know if blue is even possible to obtain....
Lasers are used all the time to drive fibre optics. If you have questions about lasers might be best to hop into the laser projector thread. This one is for LCD projectors
Lasers
I don't understand how the fibre optic was thick enough or gave anywhere near enough light to produce an image - these things aren't well known for holding a lot of light are they? Hence the name 'fibre' as opposed to 'tube'.
I'm still not convinced of mountain's claim of aiming the LED into the fibre-optic. Surely it would be like filling a bucket by peeing into a straw?
Mountain - surely you know somebody with a digital camera you could borrow from? If you were in Britain I'd post you mine. Send us some photos 🙂
I don't understand how the fibre optic was thick enough or gave anywhere near enough light to produce an image - these things aren't well known for holding a lot of light are they? Hence the name 'fibre' as opposed to 'tube'.
I'm still not convinced of mountain's claim of aiming the LED into the fibre-optic. Surely it would be like filling a bucket by peeing into a straw?
Mountain - surely you know somebody with a digital camera you could borrow from? If you were in Britain I'd post you mine. Send us some photos 🙂
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