Someone please tell me why this won't work. Found a large (50x38) fresnel with a 40" focal length.
Why can't I take a very bright (300 lumen) lcd display and build a box with the fresnel directly infront of the lcd. Just like the 70's tv magnifiers, but with a much larger focal length and a much larger total magnification achieved. Also found a place that has "hopped up" cft's that are supposed to double to 600 lumens.
With a fresnels about 92% transmission rate, this sounds good.
Sounds like a cheap 50" rear projection. What am I missing?
No optics, no focusing, simple box construction.....
---------- F
- - R
L - - E
C - - S VIEWER
D - - N
- - E
- - L
----------
Why can't I take a very bright (300 lumen) lcd display and build a box with the fresnel directly infront of the lcd. Just like the 70's tv magnifiers, but with a much larger focal length and a much larger total magnification achieved. Also found a place that has "hopped up" cft's that are supposed to double to 600 lumens.
With a fresnels about 92% transmission rate, this sounds good.
Sounds like a cheap 50" rear projection. What am I missing?
No optics, no focusing, simple box construction.....
---------- F
- - R
L - - E
C - - S VIEWER
D - - N
- - E
- - L
----------
Assuming you could get the optics to work, you're brightness is probably going to suffer. When you take an image size and double each dimension, you get 1/4th the brightness. So your 300 lumen screen, assuming you got all the light, is going to be down to 75 lumens, just by doubling the size. Assuming you make it 4 times the size, it's going to be 1/16th the brightness, or 18.75 lumens.... not a terribly watchable screen. I believe you would just be doing the "100" TV HERE ON EBAY" fresnel thing, just with a high-output LCD screen. The effects would be similar, and perhaps better with the high-output LCD. However, keep in mind that those results haven't really been that good.
Ive done it with the 100" on ebay thingy before but unless your planning on watchinig it in a pitch black room without things like computer monitors it would work. For me on the other hand I needed something stronger. Plus your going to have to invert your lcd otherwise the image will be upside down
huh?
http://www.alliedtec.com/images/107092-95.jpg
I don't agree that the image will be upside down. I'm not using the fresnel as a focusing device, like the ebay thing.... I'm using it as a viewing surface, like a typical rear screen projection. The above link is an example of what I'm talking about. I also don't agree that the lcd would be 40" (the focal length) away, the point light source would be, but the lcd would be closer. I do agree that brightness will be an issue, however that should be able to be fixed with a non columnated light source at the focal point of the fresnel, and taking the back off of the lcd. Again, no focusing optics. A flourex might just be enough light and I won't have to deal with the heat of a MH.
In a typical tv magnifier, the screen is less than a focal length away from the electron gun, not the front of the screen. Since I'm using an lcd things are a little different, but not much assuming I'm using a non columnated light.
An example of what I'm talking about is to use a gameboy, watchman, palm, or anything with a backlight and hold it a couple of inches behind one of the small 8x10 sheet fresnels. You can see the image really well at a magnified size. You can also move it forward and back and that doesn't change the focus, just the size. (up to the focal length)
http://www.alliedtec.com/images/107092-95.jpg
I don't agree that the image will be upside down. I'm not using the fresnel as a focusing device, like the ebay thing.... I'm using it as a viewing surface, like a typical rear screen projection. The above link is an example of what I'm talking about. I also don't agree that the lcd would be 40" (the focal length) away, the point light source would be, but the lcd would be closer. I do agree that brightness will be an issue, however that should be able to be fixed with a non columnated light source at the focal point of the fresnel, and taking the back off of the lcd. Again, no focusing optics. A flourex might just be enough light and I won't have to deal with the heat of a MH.
In a typical tv magnifier, the screen is less than a focal length away from the electron gun, not the front of the screen. Since I'm using an lcd things are a little different, but not much assuming I'm using a non columnated light.
An example of what I'm talking about is to use a gameboy, watchman, palm, or anything with a backlight and hold it a couple of inches behind one of the small 8x10 sheet fresnels. You can see the image really well at a magnified size. You can also move it forward and back and that doesn't change the focus, just the size. (up to the focal length)
Attachments
- Status
- Not open for further replies.