Ok, I have most of the parts I need for my projector. I gonna run my process by and what people think.
1) Make the wood enclosure, about 16" wide, 14" long and the focal length from the fresnel lens (550mm) + focal length to the the lens (gotten out of an old projector) high . Paint inside black.
2) Cut out the hole for the fan at the bottom of the enclosure (about 8" up)
3) Mount the light source to the bottom of the enclosure. Probably going to raise it 6 inches so the wiring for the lamp can be underneath. Connect all the wiring, test it out.
4) Cut out a mounting board with a 12"X9" centered hole (using a 15" LCD). Mount the fresnel lens 1 focal length from the light source (fxl halogen lamp). Put an inch gap and mount the LCD above the fresnel (since my OHP has this gap and the LCD probably should not be resting on the fresnel).
5) Cut out holes for the the power and monitor cable. Mount the LCD and securely fasten the LCD components on the side of the enclosure (AD, power board).
6) Add mirror with 45 degree angle (center of mirror 1/2 the focal length to the lens).
7) Cut out hole for lens and fasten the lens on.
8) Plug all the cables in and enjoy!
That's the main outline at least. I'd like to add some dark cloth over the fan so it doesn't leak too much light, though this would mean decreased airflow to the bulb. Also probably add some sort of board to mount all the LCD parts to. Anyways, I'll probably be starting the enclosure this weekend and any advice would be appreciated!
1) Make the wood enclosure, about 16" wide, 14" long and the focal length from the fresnel lens (550mm) + focal length to the the lens (gotten out of an old projector) high . Paint inside black.
2) Cut out the hole for the fan at the bottom of the enclosure (about 8" up)
3) Mount the light source to the bottom of the enclosure. Probably going to raise it 6 inches so the wiring for the lamp can be underneath. Connect all the wiring, test it out.
4) Cut out a mounting board with a 12"X9" centered hole (using a 15" LCD). Mount the fresnel lens 1 focal length from the light source (fxl halogen lamp). Put an inch gap and mount the LCD above the fresnel (since my OHP has this gap and the LCD probably should not be resting on the fresnel).
5) Cut out holes for the the power and monitor cable. Mount the LCD and securely fasten the LCD components on the side of the enclosure (AD, power board).
6) Add mirror with 45 degree angle (center of mirror 1/2 the focal length to the lens).
7) Cut out hole for lens and fasten the lens on.
8) Plug all the cables in and enjoy!
That's the main outline at least. I'd like to add some dark cloth over the fan so it doesn't leak too much light, though this would mean decreased airflow to the bulb. Also probably add some sort of board to mount all the LCD parts to. Anyways, I'll probably be starting the enclosure this weekend and any advice would be appreciated!
One fresnel lens is 550mm. What is the focal length of the other fresnel you are using? Also what is the focal length of your lens from the projector? What is the distance fron the lens to the screen? This info is needed to know how long to make the box.
no split design
Using two fresnel len's is just for a split design, right? I can get away with just having one, I believe. As for the distance to the screen, I'll double check the forums for the formula. Since the lens is ajustable, does this make the optimal distance to the screen variable or is it always constant. Such as it will always have to be 10 ft away or soemthing like that...
Using two fresnel len's is just for a split design, right? I can get away with just having one, I believe. As for the distance to the screen, I'll double check the forums for the formula. Since the lens is ajustable, does this make the optimal distance to the screen variable or is it always constant. Such as it will always have to be 10 ft away or soemthing like that...
Re: no split design
Split or unsplit you need two fresnels. The first fresnel collimates the light and the second one collects the light and directs it to the projection lens. There is a diagram here. http://3dlens.com/ The focal length of the projection lens has to work with the focal lengths of the fresnels. An example is you won't use a lens with a 280mm focal length with a 550mm fresnel. The diameter of the projection lens is important also as the fresnels magnify the arc image of the bulb. The final maginfied arc image size should fit in the diameter of the lens for best results.justavert said:
Ok, I guess I didn't understand a couple of things. What really confuses the heck out of me was my OHP DIY projector only had one fresnel lens and a triplet(?) lens. Is it a different sort of fresnel lens in the OHP then a regular fresnel lens?
If I get this correctly the lens should be mounted the focal length of both the lens AND the fresnel lens away. Which I'll have to get another fresnel lens that matches the focal length of the projector lens I currently have.
If I get this correctly the lens should be mounted the focal length of both the lens AND the fresnel lens away. Which I'll have to get another fresnel lens that matches the focal length of the projector lens I currently have.
Your OHP has two fresnels that are glued together. It just looks like one. The triplet focuses on the lcd panel and that distance varies depending on how far you are projecting. Once that distance is figured out you find a fresnel that closely matches that distance. I strongly suggest you build a test bed for all your optics. You can move things around to find the correct distances for your throw and then build a box once you have it all figured out.justavert said:
Mikey p said:
This is not always true, some OHPs do not worry about collimating
the light, and instead they simply direct the light, before it even gets to the transparency, to the focal lens. Thus, there are designs with only one fresnel. There are advantages (simplicity) and disadvantages (fuzziness, dimness)
Anyhow, The deal is that the first is right, you have to have lens in pairs that "match" eachother in focal length, what you do not HAVE to have are two fresnel lens. 1 will work, and you might try it out.
Ok that makes sense to me now. So if the focal length of the triplet lens and freznel lens match up the triplet would be positioned at 2X the the focal length from the light source. I'll try it with one fresnel and try both my projector lens and OHP lens and see what kind of results I get. If it does get too fuzy I'll get another fresnel lens.
On one site I noticed that the second focal length (from the 2nd freznel to the lens) should be about 1.1X the focal length from the light source to the first fresnel. Is this true? Or can I get away with having both the fresnels at the same focal length.
One more question, the longer the focal length of the fresnels the better?
On one site I noticed that the second focal length (from the 2nd freznel to the lens) should be about 1.1X the focal length from the light source to the first fresnel. Is this true? Or can I get away with having both the fresnels at the same focal length.
One more question, the longer the focal length of the fresnels the better?
Point taken, but he is building a projector. The light needs to be parrallel to pass through the lcd, and that won't happen without a fresnel. The only way it will work with one fresnel is if he is using a LED array or a parabolic reflector that is the same diameter as the lcd. Both these methods have been tried and the results are not as good as a 2 fresnel design. I have never seen a point source bulb used with only one fresnel, if you have then please post a link. I would be very interested to see it.kb18951452 said:
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