| danman589019 |
Im wanting to build my own projector and have been reading through tons of threads to get info but this forum is a little overwhelming for a noob. My first questions is what is needed to build a projector?? What I've gathered is this list
LCD
lense
fresnels
cold mirror
normal mirror
hot mirror??
type of UV blocking/filtering?
type of IR blocking/filtering?
HQI light and ballast
light box?
aspheric lense?
anything else im missing? can someone give me a brief overview or a link to a site/thread?
Im also confused about lenses..is there a specific one that should be used for something like a 7" lilliput lcd? ive seen the cheap lenses on surplusshed.com and sciplus.com and the extrememly exspensive triplet on diyprojectorcompany.com . Whats the deal?
Another thing is how screen sixe is adjusted..i have limited wall and projector space so I would need to adjust the screen size without moving my projector closer or farther away from wall ( i assume this is what everyone does). Ive seen nothing like that mentioned so i have no idea. I have some other questions that aren't coming to my head right now but these will do for now..Thanks for any help :) |
|
|
| danman589019 |
| Thanks Quin, but I have seen two of the sites and the other one (diyprojectorphils) wont work right for me. I can't get into the forums. If anyone can answer anymore of my original questions I would really aprreciate it. |
|
|
| danman589019 |
| got into the forum and read through the guide threads and some others but some questions are still left unanswered. Thanks for any more anyone can give. :) |
|
|
| Guy Grotke |
The match is really very simple. You can pick a lens that will give you the screen size and throw distance you need.
For every lens to screen distance, there is an LCD to lens distance that will give you a focussed image. The relationship between those two distances is determined by the strength of the projection lens:
1/focal length = 1/LCD to lens + 1/lens to screen
The magnification of an object to give you an image is the product of the two distances:
M = (lens to screen) / (LCD to lens)
So if you wanted a 70" image from a 7" LCD, then the magnification (M) would be 10. Let's say you want a 10 foot throw distance (lens to screen).
focal length = (lens to screen) / (M + 1)
focal length = 120 inches / (10 + 1) = 10.91 inches
10.91 inches * 25.4 mm / inch = 277 mm fl projection lens
You can also calculate the distance from the LCD to the lens:
10 = (lens to screen) / (LCD to lens) so
Lcd to lens = lens to screen / 10 = 12 inches |
|
|
| danman589019 |
| Oh I see, you just get a lense for the room...but has anyone used or made a zoom type thing so the throw distance could vary, but you would still have same size projection because you can adjust the lense ? |
|
|
| Guy Grotke |
Yes, some of the projection lenses now available at DIY projection website stores can be adjusted with a small lever on the side of the lens. This is not a real zoom, since the same focus is not maintained. So they are called "varifocal" lenses. But you can move the projector around a bit and then use the lever to change the focal length of the lens so you get the size image you need.
They don't change it by much: It is much more expensive to make a lens that can zoom over a large range of focal lengths without compromising performance. |
|
|
|
