I've just started to collect parts so that I can get started. I have a couple of lenses from and old CRT projector. They are big, and have seperate focus for the center and edge.
Has anyone else built a unit using one of these old lenses?
Has anyone else built a unit using one of these old lenses?
They have very short focal length, meaning that you have to put it very close to the LCD. people use them for their PSone LCD projectors because PSone LCD is only 5" and the CRT lens can cover it all.
by the way, what size is your CRT lenses? 6"? if you have spares, I might want one. thanks!
by the way, what size is your CRT lenses? 6"? if you have spares, I might want one. thanks!
I was hoping to use a fresnel lens as a field lens to converge the image onto the rear element of the objective lens (crt lens).
As far as the focal length is concerned, I am unable to find the value. I've read the patent information on the lens, but because there a multiple elements, and I can't fully understand the optical physics in the document, I cannot determine the proper value.
I guess I just have set up the optics, and see what I find.
As far as the focal length is concerned, I am unable to find the value. I've read the patent information on the lens, but because there a multiple elements, and I can't fully understand the optical physics in the document, I cannot determine the proper value.
I guess I just have set up the optics, and see what I find.
RE:
I have done alot of testing with a CRT lens. And 3 things I can say for sure is one make sure your lense is designed for a flat panel and two you will not get good results placing any other optics between the lens and the source. Third is that you must use a source that is smaller than the lense diameter.
Now a 4th thing I have noticed in my setup is that there is a polarization issue with my PSOne/Crt setup without the polarizers behind the lcd you will get a very red pushed dark image. Not really noticable on animations, but when you put in a movie the dark detail goes black and is almost un whatchable. This issue is worse towards the botom of the screen. I put in a polarizer and this improved but the light output dropped drastically.
I have done alot of testing with a CRT lens. And 3 things I can say for sure is one make sure your lense is designed for a flat panel and two you will not get good results placing any other optics between the lens and the source. Third is that you must use a source that is smaller than the lense diameter.
Now a 4th thing I have noticed in my setup is that there is a polarization issue with my PSOne/Crt setup without the polarizers behind the lcd you will get a very red pushed dark image. Not really noticable on animations, but when you put in a movie the dark detail goes black and is almost un whatchable. This issue is worse towards the botom of the screen. I put in a polarizer and this improved but the light output dropped drastically.
I am planning on using a 15" lcd panel. If the optics don't work out, then they will be up for sale. Time will tell. The lens is big, about 6" in diameter.
run an experiment
It's very easy to see if this lens will work with your 15" LCD. First, try a small non-frosted light bulb as your object. put the lens between the lit bulb and a white wall. Then move the lens back and forth until you get a clear projected image of the bulb. If the distance from the lens to the bulb is less than 8 inches, then you won't be be able to get a 15 inch wide image into that lens. This would be a lens designed to go right up against a CRT. If the distance is over 12 inches, then it will probably work.
Assuming it passed the first test, try taping a 9" by 12" transparency with some lines and fine text to a window during the day. Then use the lens to project an image of the transparency to the wall. (You may have to put some cardboard up around the transparency to block the rest of the light.) That will show you how the lens will handle the 15" LCD object. Don't worry if it is dim, just as long as all the corners are in the projected image. You can also do this test using two small non-frosted bulbs that are 15 inches apart, parallel to the screen wall.
You can determine the focal length of the lens using the first setup:
1/fl = 1/object to lens + 1/lens to wall
Measure to the center of the lens, not to the end of the lens.
It's very easy to see if this lens will work with your 15" LCD. First, try a small non-frosted light bulb as your object. put the lens between the lit bulb and a white wall. Then move the lens back and forth until you get a clear projected image of the bulb. If the distance from the lens to the bulb is less than 8 inches, then you won't be be able to get a 15 inch wide image into that lens. This would be a lens designed to go right up against a CRT. If the distance is over 12 inches, then it will probably work.
Assuming it passed the first test, try taping a 9" by 12" transparency with some lines and fine text to a window during the day. Then use the lens to project an image of the transparency to the wall. (You may have to put some cardboard up around the transparency to block the rest of the light.) That will show you how the lens will handle the 15" LCD object. Don't worry if it is dim, just as long as all the corners are in the projected image. You can also do this test using two small non-frosted bulbs that are 15 inches apart, parallel to the screen wall.
You can determine the focal length of the lens using the first setup:
1/fl = 1/object to lens + 1/lens to wall
Measure to the center of the lens, not to the end of the lens.
I've finally had a chance to play around with these lenses. They are BIG! 5" in diameter.
I cannot use these lenses without any other optics. They are to be mounted close to the face of a 5"-6" CRT. I've tried them with a small image source, and they do work well, but, I plan on using them with a 15" lcd.
I have a couple of fresnel lenses that I am try to work with and see if I can converge a large image into the rear element and get acceptable results. But, like I said earlier, they are big, and may be too big for my desired results for how I want my projector to look.
I think if had had a psone or lilliput lcd, this would produce excellant results. But, I don't. I'll post my findings once I've played around a little.
I cannot use these lenses without any other optics. They are to be mounted close to the face of a 5"-6" CRT. I've tried them with a small image source, and they do work well, but, I plan on using them with a 15" lcd.
I have a couple of fresnel lenses that I am try to work with and see if I can converge a large image into the rear element and get acceptable results. But, like I said earlier, they are big, and may be too big for my desired results for how I want my projector to look.
I think if had had a psone or lilliput lcd, this would produce excellant results. But, I don't. I'll post my findings once I've played around a little.
OK, I give up on using a CRT projector lens with a 15" lcd. I can get the fresnel to converge the image into the rear element of the lens, but it's like the CRT lens has a condensor lens at the rear element that is designed to bring in the whole image of the CRT face. So, when I try to use it for my set up, the only way that I can get the whole 15" LCD is on a very short focal lenght, resulting in an image about as big as my LCD and only about 14" away from the CRT lens. Not too good when I'm aiming for a 120" screen.
But, if I remove the fresnel lens, and put the CRT lens up close to the LCD panel, I can easily project the image that is with it's field of view, and project it across the room in very good detail.
So, to conclude, the CRT lens simply does not work for a 15" LCD setup. But, for a 5" LCD setup (like a psone), it would be great. Simply mount the LCD close to the rear of the CRT lens, and put a large light souce behind the LCD.
But, if I remove the fresnel lens, and put the CRT lens up close to the LCD panel, I can easily project the image that is with it's field of view, and project it across the room in very good detail.
So, to conclude, the CRT lens simply does not work for a 15" LCD setup. But, for a 5" LCD setup (like a psone), it would be great. Simply mount the LCD close to the rear of the CRT lens, and put a large light souce behind the LCD.
My 5 inch Mark IV actually cuts a 5 inch image down to about 3 so I ordered a intec controller for ps2 and am going to use that. I am still experimenting trying to see where my 2 inches are getting cut from, it is either the ring around the planer convex lens of the front barrel or the ring around the dome lens of the back peice, will post results i find or of anyone who helps for others trying this
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