[uncle eric]

I recently completed my dedicated HT room with great results. I use a Barco 808s (cinematrix moded 7700 for main source running at 960p) with a Stewart tab tentioned studiotek 1.3 gain 87inch wide 16x9 screen.

In some 'credit'scenes where there is a completly black background with white wording rolling down the screen there is a light glow around the wording. Almost like the screen is absorbing the light and spreading it round the wording.

My projectors contrast and brightness levels are correctly adjusted using both VE and Avia.

Is this normal?

Eric

 

[Jim Ferguson]

I have the Barco 808s as well, and haven't seen anything remotely like this. I'm guessing it's in the source image, not coming from the screen. To verify, take a plain white sheet of paper and stand up against the screen with the paper flat on the screen. You should be able to distinguish from that what it is you're seeing.

 

[Andrew Low]

Does the stewart screen have a backing on it? Many screens are quite thin and permit light to actually pass through them, resulting in reflections from the wall behind.


My Draper screen lets exactly this happen, which is why I'm planning to get black felt/velvet to place directly behind the screen to suck up that stray light.


Roo

 

[uncle eric]

Hi Jim,

The image itself is very nice indeed its just the credit sequences that have this weird glow around the letters/writing as they roll down.

I'll try the plain white paper idea tonight and see what happens. (what scree do you have?)


Andrew,

Dont think it has a backing, I'll check tonight. The wall behind the screen is matt black so even without a backing shouldent be a problem. Anyway, I recall that Don Stewart told me in one of his posts that there is only 3% light actually escaping behind the studiotek 130 material.


Eric

 

[Jim Ferguson]

Hi Eric,


I have the Studiotek 130, but it's the fixed-mount version. I don't believe it has a black backing on it, but it's up against a fairly dark wall.

 

[Andrew Low]

I'm interested to know how the white paper test went. My Draper screen is in front of a dark gray wall. It is mounted a few inches away from the wall so I can easily look behind to see how much light gets through.


There seems to be enough that I'm going to try to make the area behind the screen even darker than it is with felt.


One thing that jumps to mind is the lens coupling on your projector may be the result. For example, many air coupled lenses cause some minor light bounce back as the projected image passes through each lens boundary. So it may actually be in the source image, or at least the projected source.


Roo

 

[Jon S]

What you are seeing is probably not a problem with the screen. it is from the projector. i am assuming you are using a crt. air coupled crts reflect light from the crt to the lens back to the crt which lights up the crt phosphors a bit (i think this is called halation) it is most noticeable on images where there is a black to white edge (check out those james bonds opening scenes where he is tracked by a gun barrel). liquid coupled lenses reduce this light bounce back, effectively increasing contrast and brightness.

 

[uncle eric]

Jon,

Great post. Thats another thing I've learnt. I guess my next CRT will be liquid coupled. ( I assume that my Barco 808s is air coupled)

Eric

 

[uncle eric]

Jon,

Great post. Thats another thing I've learnt. I guess my next CRT will be liquid coupled. ( I assume that my Barco 808s is air coupled)

Eric

 

[Rickd]

I too have a 808 and this occurs with mine too.. I believe it is called lens flare or refraction of light in the lens of the projector producing a small ora around the bright writing with black background.


I find it happens on dark scenes too where a flash light shines out at you but it looks more like its part of the movie.

 

[kal]

For all you HTPC/CRT users, you can try this by making your desktop black and just moving your white mouse cursor around. You'll see a halo around the mouse if you look onto the CRT surfaces.


In my case it's fairly dim so you don't see much of it on the actual screen surface.


Kal


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