Ok, I have procured all essential components to start building my first projector:
Generic 17" LCD—Thoroughly disassembled and working
Opaque PJ Lens—18” FL from Ebay
Fresnel 1—330mm FL from DIYPCo
Fresnel 2—550mm FL from 3DLens
FS Mirror—8”x6” First surface mirror from DIYPco
MH Light—400w Grow type
I know that grow lights aren’t the best option but I can’t buy another light at this time. My first question is about the focus point for Fresnel 1. Should I make the distance such that it is focused in the center of the bulb (as indicated) or just in front of it to get more of the reflected light? Next, I don’t know where the main projection lens should be relative to the LCD. Should I measure the 18” FL from the outermost lens, the innermost lens, or the center of the body? I am going to make each movable +-1” for fine tuning the picture. Also, is the keystone adjustment direction correct or should it be reversed to pivot on the other side considering that it will be floor projector that might be angled upward. Please forgive the crappy image. I had to export and resize out of PowerPoint. Thanks
Generic 17" LCD—Thoroughly disassembled and working
Opaque PJ Lens—18” FL from Ebay
Fresnel 1—330mm FL from DIYPCo
Fresnel 2—550mm FL from 3DLens
FS Mirror—8”x6” First surface mirror from DIYPco
MH Light—400w Grow type
I know that grow lights aren’t the best option but I can’t buy another light at this time. My first question is about the focus point for Fresnel 1. Should I make the distance such that it is focused in the center of the bulb (as indicated) or just in front of it to get more of the reflected light? Next, I don’t know where the main projection lens should be relative to the LCD. Should I measure the 18” FL from the outermost lens, the innermost lens, or the center of the body? I am going to make each movable +-1” for fine tuning the picture. Also, is the keystone adjustment direction correct or should it be reversed to pivot on the other side considering that it will be floor projector that might be angled upward. Please forgive the crappy image. I had to export and resize out of PowerPoint. Thanks
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Put your first fresnel 330 mm from the very center of the lamp arc. That will give you mostly parallel rays through the LCD, which you will need to match the focal length of the 550 mm fresnel.
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If the LCD-to-lens distance equals the lens focal length, then your projector will focus the image at infinity. if you have a smaller room (then the whole universe 😀 ), then you can use this equation:
1/fl = 1/throw distance + 1/LCD-to-lens
For example, with a 144" throw distance:
1/18" = 1/144" + 1/LCD-to-lens"
LCD-to-lens distance = 20.57"
That measurement is to the rear principle plane of the lens, which is probably between the first lens surface and the center. Figuring out where the principle plane falls is trickey enough that it is easier to just build a quickie optical bench out of a table, a spotlight, a stack of books or wood blocks, masking tape, etc. You don't even need to use your LCD: A mockup made with some printed transparency film will do. Since you are using the fresnel for keystone correction, that throws the distance off a bit. Figure it out on the bench before you start cutting wood for the box!
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I think you have the pivot on the wrong side: With your projector pointing up, the top of the image will be too big so you need to magnify the bottom. That means you need to increase the distance between the bottom of the LCD and the fresnel. In your drawing, the bottom of the LCD has to be on the right, with the light traveling in the normal back-to-front direction.
============================================
If the LCD-to-lens distance equals the lens focal length, then your projector will focus the image at infinity. if you have a smaller room (then the whole universe 😀 ), then you can use this equation:
1/fl = 1/throw distance + 1/LCD-to-lens
For example, with a 144" throw distance:
1/18" = 1/144" + 1/LCD-to-lens"
LCD-to-lens distance = 20.57"
That measurement is to the rear principle plane of the lens, which is probably between the first lens surface and the center. Figuring out where the principle plane falls is trickey enough that it is easier to just build a quickie optical bench out of a table, a spotlight, a stack of books or wood blocks, masking tape, etc. You don't even need to use your LCD: A mockup made with some printed transparency film will do. Since you are using the fresnel for keystone correction, that throws the distance off a bit. Figure it out on the bench before you start cutting wood for the box!
===========================================
I think you have the pivot on the wrong side: With your projector pointing up, the top of the image will be too big so you need to magnify the bottom. That means you need to increase the distance between the bottom of the LCD and the fresnel. In your drawing, the bottom of the LCD has to be on the right, with the light traveling in the normal back-to-front direction.
another suggestion
Lexan XL10 is terrific as a UV filter, but it does not cut IR at all. If you put it too close to the lamp you could even melt it!
I suggest you put some kind of IR filter where you show the Lexan, then just lay your first fresnel right on a piece of Lexan (330 mm from lamp arc center). That also supports the flimsy acrylic fresnel which will warp if unsupported.
IR filters include hot mirror (best), selective plastic window films, Rosco Thermashield, DIYProjectorCompany IR filter glass, etc.
You also need a fan or two to pull that hot air from around the lamp, and dump it outside of the projector.
Lexan XL10 is terrific as a UV filter, but it does not cut IR at all. If you put it too close to the lamp you could even melt it!
I suggest you put some kind of IR filter where you show the Lexan, then just lay your first fresnel right on a piece of Lexan (330 mm from lamp arc center). That also supports the flimsy acrylic fresnel which will warp if unsupported.
IR filters include hot mirror (best), selective plastic window films, Rosco Thermashield, DIYProjectorCompany IR filter glass, etc.
You also need a fan or two to pull that hot air from around the lamp, and dump it outside of the projector.
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