I've been interested in building a DIY projector for a while and I'm finally at the point where I'm ready to proceed, but I'm a bit concerned over the lack of projectors, DIY or consumer, that meet my long throw requirements. Using Gunawan W's DIY LCD PROJECTOR spreadsheet, I find that none of the common lens triplets will work. I want to project from the back of a room to a 60" wide screen. This is apparently a very long throw, at least in comparison to the consumer projectors and the commonly available DIY projector lens. It makes me wonder. Why does noone make a consumer or DIY kit for this application? It doesn't seem it would be all that unusual. I plan on putting the projector behind a wall, which is almost 20' from the screen. And I'm limited to 60" in width, which is still a pretty big screen, at least in comparision to plasma or lcd flat panel displays (which is why I keep coming back to this project). I've worked through much of the math and physics involved, and I don't understand why this seems to be so unusual. So I'm concerned that I'm overlooking something. Why is a long throw projector so unusual? Is it something related to image brightness? Clarity? Distortion? The biggest drawback I can see is size. Long throw lens need a lot of space between themselves and the lcd panel. With a 600mm lens and an 8" lcd panel the panel needs to be about 26" away. Add a light engine and we're talking about 4 feet or so for the whole assembly. A 10" panel and 800mm lens results in a projector about 6 feet long. However that doesn't explain the lack of offerings in the consumer market, which uses MUCH smaller panels. What am I missing? BTW, there are a couple of commercial projectors that will do what I need. The cheapest one is $17,000.
Thanks.
Thanks.
There is no magic about lack of brightness, and the optics is less pretentious given the smaller angular field. The only thing is practicality. The cone (pyramid) of light will be more like a prism, so you will have to watch it from the sides if you don't want your own shadow projected too.
If you project inclined and correct with keystoning it will be easier to find a reasonable watching position though.
If you project inclined and correct with keystoning it will be easier to find a reasonable watching position though.
Hi Bemoore,
long throw PJ is uncommon in this DIY PJ, But I've already done it 2 years ago and still use it till now!
My setup is very close as yours, 550cm from PJ to the screen, 200x150cm (4:3) of proj. image.
I experimented with many types of lenses available and came up with this optimum combination: 1 positive miniscus +57cm FL and 1 minus glasseye -0,25d (-400cm FL) for total +66,47cm FL.
The drawback is: the image is not sharp as triplets but very viewable (very detail) for viewing distance 350cm from the screen.
All my friends said with a big "wow", for it after know how much it cost!
I'm still searching for Longthrow triplets, but unfortunately can be order as custom made and very expensive!
If you get better result, please let me know.
Gunawan.
long throw PJ is uncommon in this DIY PJ, But I've already done it 2 years ago and still use it till now!
My setup is very close as yours, 550cm from PJ to the screen, 200x150cm (4:3) of proj. image.
I experimented with many types of lenses available and came up with this optimum combination: 1 positive miniscus +57cm FL and 1 minus glasseye -0,25d (-400cm FL) for total +66,47cm FL.
The drawback is: the image is not sharp as triplets but very viewable (very detail) for viewing distance 350cm from the screen.
All my friends said with a big "wow", for it after know how much it cost!
I'm still searching for Longthrow triplets, but unfortunately can be order as custom made and very expensive!
If you get better result, please let me know.
Gunawan.
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