Photos are at the bottom

Update 1: Some answers to comments:

About focus: It’s not out of focus. It’s as crisp as it was with the original small screen.

About dust: The projector unit is in its own box, so dust does not go into the projector itself. If you see the photos, there is a plastic wall behind the screen and all the electronics are hidden behind and below. When you open the screen, all you see it projector lens, a concave shaped plastic walled enclosure and a mirror on the top side. I actually bought a transparent acrylic sheet and put it in the place of original screen, but it acted as a mirror and refracted the image,so I had discard it. There should be some coating available to negate the mirror effect, which means you can completely close the front with a transparent  plastic sheet.

1. Big screen TVs shrink (by perception, of course)

I bought Sony KDFE50A10 rear projection TV that has 50″ screen. After
an year or so, I started to feel like the screen size is shrinking,
really, ask any one who has a big screen TV. I wanted to buy a
projector and have 100″ screen. But with more than $2500 already
invested in the RPTV, the WAF (Wife Approval Factor) to upgrade is zero. So, I have been
thinking to convert this RPTV into a rear projector, but I couldn’t
find any help on the net.

2. Proof of concept - Is it possible?

Nervously, I opened up outer cover of RPTV with by unscrewing the 20
plus screws. Then removed the screen. Placed the TV in front of the
wall at 6 foot distance, viola!, the entire wall is filled with
picture. Clear, bright and fully focused. Will it
be good rear projector? To check out, I  bought a plastic shower curtain
from Bed, Bath & Beyond, hung in front of the TV and, ta da…, huge,
bright, clear picture and with crisp focus. Cool!

3. But, the setup should be house worthy?

I needed to figure out how to make it look good, so it won’t look
cheap or ugly. I came up with a plan. a) Build a wooden frame 8′ width by
8′ height b) Hang a screen with metal frame on this wooden frame. c)
Cover the sides, top and bottom with velvet fabric. 4) Place TV with
screen opened behind screen at appropriate height and distance.

My home theater room is in basement, about 17′ x 20′ size. I decided
to place it in corner so it won’t feel like it occupied half the room.

4. Buying the screen

Searched for a rear projection screen on the net, but most of them are
$3000 plus, except one from http://www.htdepot.com/, for $350 with
aluminum frame and velvet border. I could have also built a wooden
frame and got the fabric only and stapled to the frame., which wood have been dead cheap. But that
thought came later only after I built a wooden frame to hang the
screen. If I do it again, I would do that and save money. You can find rear projection fabric from eBay or HTdepot.com. The screen came in great package and after assembly, it looked awe
some. The screen size was 100 inches (viewable 100″, with borders 105″).

5. Building the frame

Bought four 2×2 wooden pieces of 96″ length. Got metal framing clips -
the L shaped metal pieces that join wood perpendicularly from home depot. Made a
rectangular wooden frame out of these. Stood up the frame about 6 foot
from the corner of the wall. Also bought some screw hooks (It is screw with circular head, to hang pictures) Screwed some hooks into the top wood and tied the frame to the ceiling (I have a drop ceiling) with a thin metal wire at four places, so the wood frame won’t fall. Don’t tie it permanently yet, it
may need to move to adjust the projection.

6. Hanging the screen on the wooden frame.

The screen’s aluminum frame had hooks to hang the screen. So hung the
screen on the wooden frame leaving equal gap below and above the
screen.

7. Positioning the RPTV

This is the trickiest part of all. There is no stand available that
will let you adjust height to exact tenth of an inch. So I built my
own adjustable stand. I bought two saw stands (also called work horses)
(http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100026516&N=10000003+10401001)
with adjustable height, cut a plywood in the shape of TV’ base with
extra 2 inch border around. Placed the ply wood pieces on the two
stands and my adjustable TV stand was ready! I placed rear projection TV on the stand and made height and
distance adjustments until the image from the TV fit exactly on the
screen.

8. Covering the sides, top and bottom.

From Linen n Things shop, I bought four velvet curtains. Two in red

for sides, two in black/ dark blue for the top and bottom. They were of 96″ length, so fit perfectly on top and bottom and sides as well. For hanging side curtains, I used circular hooks and metal chain (for rugged effect, it looks cool actually). I screwed one hook on the side of the frame at the top, and another hook on the wall at same height. Then inserted the chain through the curtains sleeve and tied to the hooks (I actually opened link, inserted in the hook and closed the link again). For top and bottom covering I just used nails to keep it in place.

9. Photo Gallery

Explanation of the photo is below each image.

Removed screen from RPTV

Projector lens of RPTV reflected in the mirror

Frame corners showing metal plates the hold frame together, used screws instead of nails for easy dismantle

Two height adjustable saw stands raised to correct height and plywood peice is placed on top

Rear projection screen is assemble and ready for mount. Aluminum frame covered in velvet

Side curtain in red is hung off a chain, top curtain is nailed to the frame

Keeping all in perspective - the screen, frame and RPTV

IR transmitters for components hidden in closet and Vista MCE

Rear projection in action

Complete setup

Screen shown in fully lighted room

Surnrise earth on Discovery HD 1080i picture is stunning