crt screen material query

It is probably a retro reflective material that reflects projected light back to the source.

If you are Ceiling mounting then go for reflective, one that reflects light at an opposite angle to the source, ie. down to the floor and where you are sitting.
 
gizlaroc

Your reply makes sence. But, is this actually the case?

I have read the HH data sheets and don't remember anything about the 1.8 material being retro reflective.

Regards
 
Originally posted by robwells

nfordenfield,

If you reckon you'll lose brightness, can't you go up a level in gain to compensate?

Cheers

Rob

I'm mentioning the loss due to going to a perforated screen, my screen is 1.0, so going to the 1.4 should still allow me to run the pj alot lower, it is 45 for brightness and 65 for contrast, so hope for upper 30's and 50's with the new screen material

Rgds
 
Nathan
In theory the contrast can be lowered a little, but in fact what will happen is your eyes will compensate. the picture will have a greater contrast because the whites will be brighter. The blacks will change very little if your projector is set up correctly. (or it was when I left it)
 
Brian
Gained materials vary in the way they cause light to reflect back. It is a very complicated matter once you get above matt white.

Very few act like a mirror where the light bounces off at the opposite angle. Most act like a motorway sign where the light comes back just to the driver.

So ceiling mounting a projector to work with a high gain screen will look fantastically bright whne you are standing up close to your PJ.but as soon as you sit down the image may get darker than with a matt white screen because most of the light has gone back up to the ceiling where the PJ is.

Table mount it though and the light comes back down to you. (stand up and it goes dark)

However the tubes are not in the same plane and sitting to one side or the other of the projector will cause more red or blue light to reach you depending which side you sit.

The best compromise is to use a medium gain screen ie about 1.3 BUT like all the figures they are just figures. Stewart's studio tec 130 (generaly reconed to be the reference 1.3) is not the same as Vutec's or Draper's or Da-Lite's.
 
Brian I've been meaning to do the following test for some time so thanks for making me do it.
There follows 4 pictures, not scientific experiment but it gives an idea of what happens when you use the wrong and right combination of viewing position, projector position and screen material.

I have used two projectors one ceiling mounted the other table mounted (a G70 and an BG808s). I stuck a whole load of test screen samples in the centre of the screen then viewed them from sitting down and standing up.

Even I was surprised by the results but they prove the point.

If you can't read the text
Top left = plain photocopy paper (near as you can get to gain of 1.0)
Mid top = Stewart StudioTec 130 (the industry 1.3 gain reference)
Top right = Da-Lite video spectre 1.5 (very thick screen with black backing)
Bottom Left = Da-Le high gain 2.5
Bottom right = Da-Lite Glass bead 2.8
Main screen = Harkness Hall Purlex 1.4

pictures
 
Sorry they are up now:cool:

Just got to work out how to get the sticky tape marks off the screen now :clown:
 
Am I missing something or does this not rubber stamp the HH 1.4 material?
 
Yes and No ----- because it is essentially a big screen material it is not normally used for viewing up close becuase it has quite a bit of texture.
Viewing distance is pretty much set by screen size at approximatly 1.5 to 2 time the screen width.
My screen is 9ft wide and I sit about 14ft awayand I don't find the texture too much come forwards to about 11ft and you can see it.
 
Roland

My first observation:-

There is something weird about the view angles.
Can you simply describe the projector to screen layouts?

I see a huge brightness difference in the ceiling mounted viewing positions, but the floor mounted viewing positions are similar.
Note: considering just the HH 1.4 at this stage.

Regards
 
Originally posted by Roland @ B4
Yes and No ----- because it is essentially a big screen material it is not normally used for viewing up close becuase it has quite a bit of texture.
Viewing distance is pretty much set by screen size at approximatly 1.5 to 2 time the screen width.
My screen is 9ft wide and I sit about 14ft awayand I don't find the texture too much come forwards to about 11ft and you can see it.

I had a sample of the MPS (microperf) and there ws no "texture" on it, unlike my cheapy screen now has.

Even if it did, for me a viewing distance is 11ft plus on a width of 7ft.

Roland what pj are you using to get 9ft?

Rgds
 
Nathan

I have several samples of HH screen materials and the only one that has no texture is the Matt Plus. All the others have been painted on the viewing surface, matt preview, perlux 140, 180 and spectral 240.

Regards
 
Brian
Auto matic camera i'm afriad, if you look at the intensity of the plain white paper it changes and shouldn't. I must do the test again some time but I was in a hurry.
The idea was to show how gained material , PJ possition and viewing position can effect the final out come.

Projectors were BG808s mounted on the ceiling with a Sony G70 mounted on the floor. The camera was off to the side of each projector by about a foot

Nathan my screen is 9ft wide these projectors were set to 8ft. I typed 9 for some reason. The only projector I have set up in the room that does the whole screen is a Barco Data 1209s.
 
I think I should be worried.

I put up some white inkjet paper on my screen and it lifted the image. The square of paper was noticably brighter from all viewing angles.

The white clouds on XP where whiter on the paper. Side by side it made the clouds on the screen material look dull and dirty.

I'm using an owl screen and considering it doesn't perform as well as a peice of paper it's going to have to go.


Is there any way to obtain a selection of samples. Contact manufacturers or is it just for trade? Can they be bought?
 
henry1234

Are you sure your Owl screen isn't one of those grey things for a bulb PJ?

Just call HH and ask them send you some samples.
I listed the different types a few posts up.

Regards
 
Ink jet paper may have some gain.
Really you shold be using a block of ground Magnesium Carbide. I've put mine down some where.
Nearest thing is white photocopy paper but of the few samples I have here they are all differnt.

Does ink jet paper come in 7ft widths?

I once visited a customer who painted his electric screen with white emulsion. fist time he rolled it up it turned into a laminated pole in box
 
The whole side by side comparison opened my eyes to the difference in screen material. Which until now I thought was an expensive luxury that made a tiny difference.

I hadn't considered the brighter image = lower pj contrast settings = sharper image. I was also unaware of the effect high gain screens had on viewing angles and colour shift.

I have almost no money to spend and need to think of a solution to a roll up screen.

My owl screen is 8ft wide electric but I use the centre 6ft and blank the left and right.

Would it be possible to dismantle the screen and replace the material with something like Da-Lite video spectre 1.5 or Harkness Hall Purlex 1.4?

Alternatively would it be possible to stick a piece of new screen material on top of the existing electric screen?

If anyone has tried this and failed or succeded please let me know. i would imaging there would be too many issues with creasing and incorrect tensioning.
 
I had the Da-Lite video spectra 1.5 and changed to the Draper M1300 material and I can honestly say I didn't have to alter the brightness & contrast at all so what does that tell us, it is also a very smooth material I would recommend it. I use a Barco G808s in a totally black room.
Hope this helps.

Dave
 
I have just ordered some M1300 fabric from Henry @ CRT Projectors:D
54" X 96"

I bought my 808 from them about 1 year ago & I trust his comments are reliable that this is 1.3 gain (he uses it)

Apparently the fabric has no texture at all and you can view the picture by looking across the screen surface

It turned out not to be that much more than the HH stuff including delivery from the USA and VAT
 
just to round off this thread, I'd like to add that I've settled on brightness at 40, contrast at 70 and the gamma for the overlay on my radeon card(hcpc) set to 2.2.

This gives a good vibrant picture as is, and I've yet to set it up with avia.

See attatched (shakey/digicam) pic for a rough estimation.

Cheers

Rob
 

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