First off all i hope this is new to the forums and in giving something usefull to those trying out there. This was done as part of my recent plans on building a Pj for my family. A concern was raised by the fact that: this is not my house, i dont want to drill holes in the roof and i dont want to have a huge box in my line of sight. An option of mounting it at an angle was given and here i examinate the usefullness of it. my calculations are here. i will explain everything done there.




well, i took precalculus 6 years ago, a professor said i would use it the rest of my life, he was kinda right. i didnt remember the exact way to do it but i remember it was there in the book in trigonometrics section.

The screen i want is 84 inches. Using the focal calculator that gives me a distance of 6.92'. i want the projection either at 70'' or at 54'' from the ground. the calculation was made with a 10º angle but i had the doubt of how much the drop in height, of the projector at a table, would be. that doubt is X. So to find that X i have to use this formula: X/distance from wall = tangent of angle.

This can be simplified to X =tangent of the angle *(multiplied) by distance from wall. this is my own result:
using a 10º angle
X=6.92(tan 10º)
X=6.92(.1763269) this tan of 10 is found using a science calculator.

X=10inches. this is a complete coicidence.

using a 15º angle
X=6.92(.2679)
X=15 inches coincidence again

notice that the farthest away that you are the bigger the drop would be.

i measured my line of sight sitting in the couch. It was 45''.

so if i mount it to project at 70''(this 70'' would be the center of the image) the triplet would sit at a height of 60'' at 10º or at 55'' at a 15º angle. that would block my line of sight and may make watching the screen unconfortable.

if it projects at 54'' the pj would be at 44'' at 10º or at 39'' at 15º. that sounds better.

now this can be mounted from the roof too. in that case the angle calculation would be added and not substracted. for instance: if it is projecting straight it would sit at 70'' but at a 10º angle it would sit at 80 inches from the ground. at 15º angle it would sit at 85'' from the ground.

im not totally convinced yet and i think ill build the pj and then i will take the choice based on what i find is more confortable for me and my wife.

i hope this has helped anyone. if theres any ?? ask away!!!

no comments?????

am not entirly sure what you are trying to find but...

if your are projecting at an angle of say 10 degrees and have an a required distance of 6.92(this becomes the hypotenuse, the long side).
with sin x=opposite(distance up the wall from middle of the triplet)/hypotenuse(6.92).
and since x=10 you should be able to find how far up or down the wall you are going to be projecting(sorry i dont have a calc on me!).

hope that was of some help but if i didn't answer what you are needing reply back and will try to help.

sorry i wrote X=10 in the paper but what i was looking for was X. The result is 10inches below the wanted project image at 10º. I posted this as a method to calculate the height, where the projector will sit if you want to project at a certain height in the wall and at a certain angle. I wanted to determine if the pj would sit below or over the line of sight and if it would make me change the arrangement of the family room.