Projector height calculations. - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-24-13, 01:57 PM Thread Starter
Shackster

Join Date: Jul 2010
Location: Tacoma Washington
Posts: 15
Projector height calculations.

Hello everyone.
I am trying to determining the correct altitude for the projector.

After going through the Calculator Pro I did not see any input
or output specifications for the proper height of any given projector.
I know most projectors have minimal horz. & vert. offset adjustments.

My question is what would be considered a ideal starting point?
Do you start at dead center parallel with the screen then raise
the projector up until you can see under it?

What is the maximum off center vertical before you have problems?

Here are the specs and projector I am consider now.
Room:
Throw distance available 0' to 21'
Max available screen wall 11' 3" wide by 8' 5" ceiling
Would like to place cabinets under screen 24" to 28" height max
Seating space available 0' to 21'
Screen, any top quality manufactured
Ambient light control, absolute zero to any level
Walls and ceiling black to dark midnight blue flat paint.
No windows.

Projector considering:
Panasonic PT-AE8000
Calculator Pro settings I came up with:
16.9 aspect ratio
17' 7' throw distance
5' 6" tall screen
11' 2" diagonal screen
9' 9" wide screen
Seating, 13' 8" to 21" 5"
Screen gain 1.0

Considering this information how would I derive projector height?
GalaxyDrifter is offline

Old 02-24-13, 09:20 PM
Senior Shackster

Join Date: Aug 2010
Posts: 487
In an ideal world it would be best to have the projector inline with the center of the screen, but for most people that would not be...ideal. In the real world, Panasonic includes enough "tweakabliity" that you could mount directly to the ceiling and have everything work. Your post almost reads like your goal is to make the biggest picture possible, but that is not always the best choice. I would decide what would be the closest I would want to sit, and calculate the screen size that would give a 35 degree viewing angle. Then decide the furthest seating distance and calculate the screen size that would give a 25 degree viewing angle. The average of those sizes should be about perfect for the room. Next position the screen at the height that gives everyone in the room the most comfortable viewing angle. Consider if the rear seats will be elevated. Now that you know the height of the top of the screen and the seating positions and heights, 2 things remain. Throw distance is adjustable, but on some projectors the brightest image is only available at the shortest throw. I'm not sure about the 8000, but I know this was the case for the 4000. I would set the projector just a few inches more than the shortest throw that would give me my desired screen size. Now we are finally ready to look at projector height. Center height of the image is usually not practical, so move up until you are above everyone's sight line. The next thing to consider is the projector being bumped. Depending on location, you may want it high enough for your tallest friend to walk under it.

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People think I'm strange, does it make me a stranger?
phreak is offline
Old 02-25-13, 04:48 PM
Senior Shackster

Join Date: Jul 2011
Location: Boston, MA
Posts: 125
Re: Projector height calculations.

The more vertical shift you use, the more the focus will be skewed across the image. There are practical concerns, of course - you don't want to be bumping your head on a projector. For most projection setups, the vertical shift available is several times what you need, so there is no issue there. The equation to figure everything out looks something like this:

{shift distance} = {distance from screen center to ceiling} - {projector mount drop distance}

{shift distance} / {image height} < {vertical shift ratio}

Given the target image height and possible vertical shift of your projector, you can calculate the minimum drop distance. You will likely find a negative number there, meaning you could mount the projector above the ceiling and be fine.

My JVC RS55 has an 80% shift (.8 shift ratio), and I'm using about 20%. I don't notice any issue with it at all. On my previous Epson HC720, I was using close to 40%, and that was barely noticeable.

Your PT-AE8000 has 100% vertical shift (1.0 shift ratio) and 26% horizontal shift (.26 shift ratio). If you run through the equations, you will likely see that you don't need anywhere near as much as 100% V shift, and you should shoot for 0% H shift. In my opinion, horizontal shift should be avoided. You don't really get any benefit using it unless there is a pole in the middle of your room or something, so why introduce that skew. The equations are the same for horizontal if you need it, just in the different direction.

jimbodude is offline

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