Originally Posted by johnorloff
Tryg-- Great review and series of posts!!!
I noticed that your projector is 8' from the ground, and presumably the HP screen is NOT. Therefore your lens is not centered on the screen, or close to eye level as Da Lite recommends for optimal gain with the HP....
Hopefully I am getting all that right, because I have a simliar-- if a slightly smaller scaled-- version of your set up. My Pearl is about 7' off ground, and level with the top of my 92" Da Lite screen (currently Hi Contrast Cin Vision). I'm not entirely satisfied with the brightness (I'm at the far end of the throw range at 15'), and was hoping I might get a little extra juice out of the HP screen.
The nice guy at Da Lite wasn't sure, due to the placement of my projector about 4' above eye level... He is sending me a sample, but at 6"x6" the sample might be hard to really answer the Q...
Any thoughts from ANYONE would be GREATLY appreciated. Anyone have their HP paired with a ceiling mounted projector?? Is it worth it if the "sweetspot" is when I'm standing??? Think I would have a gain worthy of the extra cost??
If your pj is 4' above eyelevel then the angle of incidence is easy to determine
from how far back you sit. (Angle=arctan(4/d)).
Here are some examples:
d=10 Angle=21.8 Approximate gain=.87
d=11 Angle=20 Approximate gain=.9
d=12 Angle=18.4 Approximate gain=1.15
d=13 Angle=17.1 Approximate gain=1.25
d=14 Angle=15.9 Approximate gain=1.35
d=15 Angle=14.9 Approximate gain=1.45
d=16 Angle=14.0 Approximate gain=1.55
For comparison here are the same estimates if you drop the
pj to 2.5' above your eyeball.
d=10 Angle=14 Approximate gain=1.55
d=11 Angle=12.8 Approximate gain=1.7
d=12 Angle=11.7 Approximate gain=1.82
d=13 Angle=10.8 Approximate gain=1.95
d=14 Angle=10.1 Approximate gain=2.1
d=15 Angle=9.46 Approximate gain=2.2
d=16 Angle=8.8 Approximate gain=2.27
In the situation the bqmeister describes above the angle off axis is about 5 degrees. This gives a gain of 2.6 which is very close to the max of 2.8.
Note: These calculations are based on DaLite's chart for Gain vs Degrees off axis.
They are also assuming that the only offset is vertical. Add in a horizontal offset
and the gain drops further.