Hello, glad to finally find an active forum that deals with this subject.
I do not have the same needs as someone building a home theater. This is for an art project and I have a few specific parameters, so I'm not sure whether I should buy all the parts and assemble, or start with an overhead and lcd panel, or (I don't know if this is possible) buy a cheap commercial projector, take apart the casing, and replace the lenses and bulb for my purposes. Here are my parameters:
I want to project images sized 18" to 24". The image will be projected upwards onto a spherical mirror of that size hanging from the ceiling. I am hoping for a distance between 10-15 feet from projector to target. I don't expect the best quality out of reflecting onto the mirror but I'm pretty sure it's doable, I've seen it for other applications.
Since the point is for the mirror to reflect the image onto the room, I need it to be adequately bright at a total distance of 20-30 feet, and then there's the corners of the room that will be further, and the probability that the mirror will by definition decrease brightness. So first I need to know what kind of bulb I need for this purpose.
I also need to know what size lcd and types of lens I should get (I found the focal calculator on lumens but that place is inactive and won't let me register to download the file). I imagine the smaller size the better, but how small is too small? Or will this not matter if I have lenses with a very long focal length? (I found 7" TFT lcd displays on ebay for cheap, are these usable?)
I am aware that I can settle with a larger resulting image and just shrink my video file so it fits the 18-24" and I'm willing to if I have to but if it's possible to get this small of an image without tiny low-res lcd's I want to try that.
I also want to insert painted plexiglass slides to be superimposed on the lcd's images. So if I were building this myself, would I put the slides inbetween the fresnels with the lcd? Would this alter the required focal length of the fresnels since it adds a half inch (to be safe) to the thickness of the lcd? If I used an overhead would I basically place an lcd panel above the light, and the slides above that?
So mainly because of the size and distance I want, I'm not sure which route to take. If I can get a cheap commercial projector and change the lenses (and bulb?) while fitting in a slot for those painted slides, I think I'd prefer that. If not but I can use an overhead + panel and switch the lenses is that worth it over going completely diy? If I would need to switch the bulb in the OHP as well would there still be an advantage? And if I do it the hard way what do I need? I'd be very grateful to hear what you think.
I don't care how the physical object looks, even if it's several feet long because of the focal length, but I will do my best within my student budget to make the projection be of passable quality. Thank you for reading.
I do not have the same needs as someone building a home theater. This is for an art project and I have a few specific parameters, so I'm not sure whether I should buy all the parts and assemble, or start with an overhead and lcd panel, or (I don't know if this is possible) buy a cheap commercial projector, take apart the casing, and replace the lenses and bulb for my purposes. Here are my parameters:
I want to project images sized 18" to 24". The image will be projected upwards onto a spherical mirror of that size hanging from the ceiling. I am hoping for a distance between 10-15 feet from projector to target. I don't expect the best quality out of reflecting onto the mirror but I'm pretty sure it's doable, I've seen it for other applications.
Since the point is for the mirror to reflect the image onto the room, I need it to be adequately bright at a total distance of 20-30 feet, and then there's the corners of the room that will be further, and the probability that the mirror will by definition decrease brightness. So first I need to know what kind of bulb I need for this purpose.
I also need to know what size lcd and types of lens I should get (I found the focal calculator on lumens but that place is inactive and won't let me register to download the file). I imagine the smaller size the better, but how small is too small? Or will this not matter if I have lenses with a very long focal length? (I found 7" TFT lcd displays on ebay for cheap, are these usable?)
I am aware that I can settle with a larger resulting image and just shrink my video file so it fits the 18-24" and I'm willing to if I have to but if it's possible to get this small of an image without tiny low-res lcd's I want to try that.
I also want to insert painted plexiglass slides to be superimposed on the lcd's images. So if I were building this myself, would I put the slides inbetween the fresnels with the lcd? Would this alter the required focal length of the fresnels since it adds a half inch (to be safe) to the thickness of the lcd? If I used an overhead would I basically place an lcd panel above the light, and the slides above that?
So mainly because of the size and distance I want, I'm not sure which route to take. If I can get a cheap commercial projector and change the lenses (and bulb?) while fitting in a slot for those painted slides, I think I'd prefer that. If not but I can use an overhead + panel and switch the lenses is that worth it over going completely diy? If I would need to switch the bulb in the OHP as well would there still be an advantage? And if I do it the hard way what do I need? I'd be very grateful to hear what you think.
I don't care how the physical object looks, even if it's several feet long because of the focal length, but I will do my best within my student budget to make the projection be of passable quality. Thank you for reading.
I think when you say you want to project an image of 18" to 24" you are incorrect as all the mirror will do is fold the optic path. I actual effect you want to project an image size which will cover the whole floor span of that room. Unless you have a really short throw lens, there is not a projector that can project upright from the floor to the ceiling and produce a 24" image. Also the projector itself will be in the way of the light path. I think your best bet is to ceiling mount it and shine it at the mirror at 45 degree angle however it may be a challenge if the mirror is spherical in shape. You may achieve your objective with a commercial LCD projector and using transparencies which can take excessive heat in place of the LCD panels.
Thank you for responding gizmotech. But I don't understand what you mean by "folding the optic path". I imagine that light pointing up at a spherical mirror from a source straight below will be scattered in all directions below the mirror, that's what I want. I figure that I want the image size to be 18-24" so that as much of my image as possible hits the mirror and gets reflected. Yes, I want the digital movie that I'll be running through the projector to be the size of the room but I believe the optical image needs to be the size of the mirror in order to fit all of my digital movie on it and be reflected (For now I won't mind any abberations or reduction in detail). And don't I need a really long throw lens to keep the image small? A short throw lens would make the image larger no? I am not worried about the projector being in the way, my project is planning for there to be a shadow in the middle of the room. As for ceiling mounting, well I want to be able to have physical access to it while it's running so I can change those glass slides I mentioned on the fly. Also if the projector is on the floor and the mirror on the ceiling that is the widest possible angle of reflection across the room (walls, floor). I am wondering if I can mount the mirror on a wall and point the projector straight at it from only a few feet away, but that would leave a much larger shadow by the projector which I don't want. Regardless I can still use a projector with a normal throw lens, and digitally shrink my movie and use smaller glass slides to fit on the mirror, as a last resort. Are you able to tell me where in the anatomy would I place the slides so that they are in focus? In between the fresnels with the lcd panel? Thank you again.
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