Hi ya. Got your PM's, thought I'd answer here.
I know this problem as I have it myself.
There is actually 4 possible issues going on, this is why it can be difficult to resolve.
Multi choice
1. Projector placement.
2. Projector rotational alignment.(different to 1.)
3. Lens distortion.
4. Screen isnt flat, square.
5. All of the above.
Tools required.
(cheap method)String line, tape measure, rule
or laser level with laser sighting(really exellent tool to get screen centralised).
First thing to check. Your wall.
Grab an assistant:bigsmile:....now now......with your string line check how flat your wall surface is. Do this by having your assistant hold the string line against the wall following the bottom edge of your screen area. Keep the string tense as you at the other end approach the wall suface with the string.
Follow it in by looking down the string path as you get close to the surface.
If the wall is flat the string will connect when you touch the string to the wall. You will see no hollows under the string nor will it deviate along it's path.
If the wall is curved the string line will contact at the peak point then bend the string. It will be obvious.
If you see a hollow behind the string you have a pre built concave screen:bigsmile: Maybe not desirable unless you are doing anomorphic.
Repeat process corner to corner, virtical, top edge, bottom edge.
If the wall is out you have to repair to proceed.
Because I used MDF I was able to pack behind my screen to get it flat.
In fact if the wall is badly out, using a sheet of MDF or substrate is a cheap repair.
PJ alignment.:gah: This takes careful care.
With a 4 directional laser level, find the center line of the bottom of the screen.
Rotate the laser beam up slowly, if the projector is in the correct spot the beam should hit in the middle of the lens. Simple....yuk yuk yuk.
Cheap way.
Take your string line. You actually need 2 bits now.
Make a plumb bob, weight on the end, with a point so you can accurately pinpoint things.
From the center line of the screen, drop the plumb bob from there. Where the point strikes the floor is where you start a string line. Stretch out the string line under tension so that you go past the projector. You need your luvly assistant to hold the end by the wall as you get the line square.
Square=>3,4,5 princple, with a triangle if one side is 3 and the square(90degs) side is 4 the connecting line is always 5. This can be any size as long as the arrangement is the same multibles of 3 4 and 5.
3ft 4ft and 5ft, or 9ft 12ft and 15ft, applies with metric aswell.
Now measure 3ft from the centerline, make a pencil mark on the wall.
Measure 4ft along your string line, mark the string at 4ft.
With your tape measure arc a 5 ft path from the 3 ft wall pencil point.
You then bring the string line 4ft mark and tape measure (5ft) together, tension the string line out past the projector and ta daaaa you have a square line from the screen.
Drop a plumb line down from the projector lens centerline.
If you are perfect the plumb line should touch your screen string line.
If you are off 2 things could be wrong.
1. rotation
2. PJ Squareness.
If you rotate the PJ until it lines up the projector may be still off square.
At this point you find out how good lens shift is if you have any.
This can be tricky to comprehend, remember you have a double hinge going on here. Typically the PJ is pivoting around a different center line than the lens center line. When you rotate the PJ the lens is sweeping on an arc, the lens shift is another pivot point.
The aim is to have the lens itself aligned with the screen.
It is very likey that you are off and you make need to reposition the screen or PJ, which ever is easiest.
Distance, Lens shift. This is where I need to remount my PJ.
I need to be a little further away and lower.
With consumer grade stuff compromises are made. Lens is an area where some spend fortunes just to be optically correct.
You are always best to minimise lens shift and Zoom functions on consumer grade gear. I am getting optical distortion because I am set at 3m(12ft) from the screen and have wide zoom. If I pulled my PJ back about 1m(3ft) and lowered it about (300mm)1ft I would fix the edge bending optical distortion.
:thud:
:whew: And I thought I was going to write this in 5mins.....so much for lunch break:wave:
PS, keystoning is nasty, I have now seen the light, seen what it does and is really something to be avoided.
With a 720 type PJ running on NTSC or PAL 1 click of keystone won't be noticable.
But if you run HD 1 click of ketstone will damage the image to the point of dropping the HD to SD or somewhere between.