Instead of making a new topic I'll just post this here..
I've been thinking of going passive 3D and this is my first projector project ever, so I thought I finally found enough information to get things started, but then I see this: "Since the colors from your projectors are aligned 0/90° you need to use 45/135° filters and glasses. If the filters are aligned 45° from the polarization..." Whaaaat?
Hi and welcome!
This is technical info but it's important in the choice of going 0/90° or 45/135° with a passive rig and LCD-projectors
Why? Lcd-projectors already have an internal polarization and on top of that the colors are not even having the same polarization! Let's say two colors share one polarization (for example 0°) and the remaning color have 90°. If your polarizer is aligned either 0° or 90° it will kill some of the colors from the projector. If the polarizer instead is aligned 45° or 135° all colors slips through equally. You get a slight loss of intensity but it's is similar to a dlp-projector passive setup because the light from dlp's have no polarization alignment. Spar-filters (lcd-projectors only!) have retarderlayers which aligns all colors before they get to the final polarizer which means that you'll have a very high light throughput.
If you're aware of how this works you can easily try using ordinary polarizers for a start, even with lcd-projectors! You can easily upgrade to stereopol filters later on if you feel need of extra light which is not possible with dlp's.
Projectors being the same? This is important! If the alignment of pixels differ because of different optics properties of the projectors you may get strange phenomenas. These are specially noticed when viewing 2d but if the phenomenas aren't too big, then 3d is very forgiving in reproduction. Less visible in 3d in other words.
To find out your projectors polarization of lcd's? Most probably they are 0/90° from the beginning. If you want to check:
If you have, it's easiest to use a couple of polarized glasses where you already know the polarization angles. Hold the glasses in front of the projectorlense and look at the screen image. Either you get a full color (no colors killed) view when the glasses are straight or when you turned them 45° in either direction. If you get a full color view when the glasses are STRAIGHT then the glasses you have are the ones to use!
If you don't know the polarization angle of the polarization filters/glasses it's still possible to determine for as long as you have at least two filters but it's tricky to explain how: Hold both filters in front of you and rotate one of them until they block entirely. Then turn one filter without rotating any of them. The closer to 0°/90° you have the less difference you'll see in blocking and the closer to 45°/135° the bigger difference you'll see.
You'll get no polarization phenomenas when using dlp-projectors but you can also not use special spar-filters either (which means a steady 55% light loss using dlp's). However: even using dlp's you get twice as much light as when using shutters because of the two projectors! Lcd's and ordinary filters matches dlp's in lightemission but as said: filters needs to have the right alignment (most probably 45°/135°) to maintain colorreproduction. Lcd's and spar-filterss have a light throughput up to 85% (15% loss) which gives almost twice as much light as when using standard polarizers.
Regarding keystone you're partially right (in regards it doesn't totally messes up the image
): When mounting projectors and not having them totally right in height the picture shown is trapetzoid. To correct this you need lenseshift or keystone correction.
Lenseshift works in a mechanical way to adjust til the picture is a perfect rectangle.
Keystone correction is made digitally which means that the image is increasingly scaled vertically to make a perfect form. Since nothing in the projector is moved mechanically this can only be done by reducing the pixels. This will result in 1: Less resolution and 2: phenomenas where the picture becomes blurry because of the keystone algoritm.
My projectors don't have lenseshift (but i wish they had) so i have to stay with keystone correction.
Without keystone correction the flat picture in 3D will look scewed, like a bent paper. However: when turning on 3d this effect is experienced less because of the depth in 3d-image. The closer the lenses are to each other, the smaller this phenomena becomes. With keystone and lenseshift you can correct this to a good rectangular image on both screens (resulting a perfectly shaped and not scewed image).
Myself i prefer a keystone corrected image instead of without but to reduce aliasing phenomenas i play my games in a higher resolution than the native resolution of the projectors. This reduces the experienced blurriness of the projectors keystone because the projectors now also have to scale the image. In my case using 1280x960 gives a great image even if the native resolution of projectors are 1024x768. The alignment of the projectors i have now gives a keystonevalue of -2% on one and +4% on the other projector so it's probably as good as it can get anyway.
Regarding silverscreen: Check with the homepages of different screenmakers. Most of them sells the screens with frames but this usually costs quite a sum. So i decided to make my own solution and only buy the pure screenmaterial.
Tip: Don't do what i did from the beginning in the eager to make it work! I nailed it up on the wall using pins which of course in notime resulted in a dropdown with permanent wrinkles...
Different screens has different mechanical properties (check Sharky's thread) and can be mounted different. I'm using a silverfabric silverscreen attached to a rollercurtain which i roll up and down on a tube. It works for me but this screen might have to be stretched to look good (Sharky has the same and had to while i manage without). There are also paints but i have personally no experience of them.
Mb: Asus P5W DH Deluxe
Cpu: C2D E6600
Gb: Nvidia 7900GT + 8800GTX
3D:100" passive projector polarized setup + 22" IZ3D