Xterrian:
I think the parabolic mirrors are going to cost too much. I could not find a 16" parabolic mirror for less than $5000. This is far more expensive than getting an 18" fresnel lens from fresnel tech for $120.
Here are the parabolic mirrors from EO:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?Productid=1660
You could go the other route like those of us who bought OHP's, and instead buy a reflecting telescope for its optics. However, I doubt you can get a large aperture reflecting telescope very cheaply.
Good luck,
CR
I think the parabolic mirrors are going to cost too much. I could not find a 16" parabolic mirror for less than $5000. This is far more expensive than getting an 18" fresnel lens from fresnel tech for $120.
Here are the parabolic mirrors from EO:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?Productid=1660
You could go the other route like those of us who bought OHP's, and instead buy a reflecting telescope for its optics. However, I doubt you can get a large aperture reflecting telescope very cheaply.
Good luck,
CR
I'm not sure exactly how it works, but the secondary mirror doesn't block the starfield when you look through the telescope, so I have to assume that it won't block the LCD either. I would think that you wouldn't need a primary mirror larger than the LCD you are using. There are ATM(Amature Telescope Maker) sites that show you how to make your own Parabolic mirror. After reading the instructions, I don't think it would be all that hard, just time consuming. The only real problem I see is the focal length of an f8, 8 inch mirror is something like 46 inches. That might be a bit long. I'm still looking into it and will post a drawing once I do the math and come up with something reasonable.
Instead of buying a $1000 high grade parabolic mirror to reflect light from a cheap bulb, why not just make the mirror yourself? A decent quality mirror surface that would work great is aluminized mylar (I posted this before but nobody listened). And a spherical mirror can be made very easily since the center of curvature is constant. I recently made a rather large spherical mirror (about 1m diameter) for a solar hot dog cooking contest. Despite the fact that the mylar was applied VERY poorly in about half an hour, the light was still reflected rather well. (I looked at the mirror from the focal point to see how much light from the sun was reaching it. Needless to say, LOTS of light was reaching it. Everything I saw for about 10 minutes afterwards was yellow! 
)
In fact, you could make a good mirror really easily by taking an old satellite dish, stripping the paint off, and applying the mylar. Of course, this is all assuming you have a light source that is an ideal point. Maybe I'm missing something, but I'm not sure why everyone is focusing on parabolic mirrors when a spherical mirror can be made very easily, much easier than a parabolic. Both parabolic and spherical mirrors assume a point light source. So making a spherical mirror would be the way to go. Just find a material to shape the dish. Then use a cutting tool attached to a sweepable arm centered above the material. Sweep the tool around till the dish is formed. Then, apply mylar. That's all it takes, really. Even buying high grade mylar will be dirt cheap for the size of reflectors we're talking about. The only real issue would be the geometry of the light. I don't know enough about all the different light sources you guys are using, but whatever system is closest to a point light source would obviously work best. I've been looking into cold cathode tube lights. An array of these lights with trough style reflectors could work well. The only issue is brightness. I can't find any light-related data on easily attainable (computer case) CCFL lights.
)In fact, you could make a good mirror really easily by taking an old satellite dish, stripping the paint off, and applying the mylar. Of course, this is all assuming you have a light source that is an ideal point. Maybe I'm missing something, but I'm not sure why everyone is focusing on parabolic mirrors when a spherical mirror can be made very easily, much easier than a parabolic. Both parabolic and spherical mirrors assume a point light source. So making a spherical mirror would be the way to go. Just find a material to shape the dish. Then use a cutting tool attached to a sweepable arm centered above the material. Sweep the tool around till the dish is formed. Then, apply mylar. That's all it takes, really. Even buying high grade mylar will be dirt cheap for the size of reflectors we're talking about. The only real issue would be the geometry of the light. I don't know enough about all the different light sources you guys are using, but whatever system is closest to a point light source would obviously work best. I've been looking into cold cathode tube lights. An array of these lights with trough style reflectors could work well. The only issue is brightness. I can't find any light-related data on easily attainable (computer case) CCFL lights.
Dammit
I know that DUKANE 680 is an excellent OHP that delivers 7800 lumens to the screen. Plus it has excellent optics and when you touch the fresnels after 30 minutes of work, they are relatively cold. the only downside is that even on ebay.com it costs about $150. that is a lot of meny for a light source. i am planning to spend about $250 on the LCD panel first and then get the best OHP that i can afford with the rest of my funds.
Can anyone help me make a choise regarding the type of OHP that i should get. i need a bright, quiet, and cool lightsource. it anyone has any ideas let me know please.
Aleksey
I know that DUKANE 680 is an excellent OHP that delivers 7800 lumens to the screen. Plus it has excellent optics and when you touch the fresnels after 30 minutes of work, they are relatively cold. the only downside is that even on ebay.com it costs about $150. that is a lot of meny for a light source. i am planning to spend about $250 on the LCD panel first and then get the best OHP that i can afford with the rest of my funds.
Can anyone help me make a choise regarding the type of OHP that i should get. i need a bright, quiet, and cool lightsource. it anyone has any ideas let me know please.
Aleksey
xblocker is right
An externally hosted image should be here but it was not working when we last tested it.
Missing the point.
Why magnify/concentrate the heat producing light before you run it through your delicate LCD? Let's amplify it after it passes through the LCD. Do you put the amplifier before or after your headunit? It just doesn't make sense to me why anyone would even consider it the other way around.
Why magnify/concentrate the heat producing light before you run it through your delicate LCD? Let's amplify it after it passes through the LCD. Do you put the amplifier before or after your headunit? It just doesn't make sense to me why anyone would even consider it the other way around.
Amplify?
Theres no need as I posted earlier my 400W MH is wraped in foil with a small hole by the acr tube cut out and this is what I get.
Something wrong with that?
Theres no need as I posted earlier my 400W MH is wraped in foil with a small hole by the acr tube cut out and this is what I get.
An externally hosted image should be here but it was not working when we last tested it.
Something wrong with that?
prjctr_builder,
I have a 3M 1705 OHP which is quite good at 2000 lumens with a 52 inch wide picture contrast and brilliance are about half way and the picture is very satisfactory even with some low level lighting on.
Bulb type is EHJ. Fan noise level is not noticable even during quiet parts of a movie and the glass stage stays cool after several hours use.
I have a 3M 1705 OHP which is quite good at 2000 lumens with a 52 inch wide picture contrast and brilliance are about half way and the picture is very satisfactory even with some low level lighting on.
Bulb type is EHJ. Fan noise level is not noticable even during quiet parts of a movie and the glass stage stays cool after several hours use.
xterrian,
to have a given brightness there must be a transition of a given light flux through the panel, Now if you would place a fresnel condensor between panel and projection lens, this would mean:
1. image quality decrease, because fresnel now is within the image path. Fresnels have no good imaging quality! This would also affect the focal lenght of image path!
2. Lightsource must move towards the panel to get the lightsource collimated into projection lens.(heat! No protection of the panel)
All condensors in projection systems are placed directly after lightsource because little unperfectness of the illumination systems is less critical than unperfectness of the imaging system!
xblocker
to have a given brightness there must be a transition of a given light flux through the panel, Now if you would place a fresnel condensor between panel and projection lens, this would mean:
1. image quality decrease, because fresnel now is within the image path. Fresnels have no good imaging quality! This would also affect the focal lenght of image path!
2. Lightsource must move towards the panel to get the lightsource collimated into projection lens.(heat! No protection of the panel)
All condensors in projection systems are placed directly after lightsource because little unperfectness of the illumination systems is less critical than unperfectness of the imaging system!
xblocker
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