Newbie with Question about Throw distance

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OK, I have gotten the bug to build a projector. I have been working on building my own home stereo for a while and now want to add a projector to the mix. I have read almost all the posts in this forum and the ones at DIY Projector Company. I have sort of decided on my design, the MKIII from DPC, the demintions will allow it to set nicely on the breakfast bar above my couch.

The question I have though is how do you figure the size of the displayed image from the throw? I have noticed that most people here have a throw of about 10', I measured my family room last night and found that if I put the projector where I want to I will have a throw of about 22'. Is this going to make the dispalay too large with a 15" lcd monitor system. My wall for the screen is 10'w X 8' h. I plan to build a custom screen from a wood or pvc frame with BO cloth streached over it since the wall is mirrored.

Since I have such a long thow would I be better to build a 7" lcd projector like the DPC Pico? I would think that since you are starting with a smaller immage you could move the throw back further without making the image too large for the wall.

If any one can help with this it would be greatly appreacated. I am just in the planning stages on this project and need all the help I can get.

Also if anyone has any plans or drawings for a projector I would be intrested in seeing them.

Thanks much
Kerry
 
Hi Kerry,

You need to play with this equation:

An externally hosted image should be here but it was not working when we last tested it.


After plugging in the focal length of so called long-throw lenses available to us (450mm), you end up with a very large image! Unless I've bodged the numbers ~5m.

Using a 7" lilliput would just over halve that, which is probably a bit more realistic.
 
Thanks Quin, I looked at those equasions yesterday and then totaly forgot about them. It looks like I will be building a 7" lcd system since it will produce about a 9' diag image with the lenses from DPC. If I used a 15" system with that throw it would be over 20' diag, that would be cool but kind of large for this room.

I guess now I have to find a design. I have been looking at the PICO from DIY and probaly will go with that although I would like to build one with no mirrors.

On with the planning....
 
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