BG801S - A Good Image at 10ft!

Nathan (nfordenfield) popper over last night to work out where my BG801S will have to sit on the floor in order to run under floor trunking to the correct spot.

I don't have a screen yet, but a dust sheet over the window at 8ft produced a wonderful image, even without blinds on the windows.

Out of curiosity we pulled it back to 10ft, this would be a good size as it will cover the window's width completely. The picture was more than acceptable, it was very good. Not as clear close up, but at the 20ft viewing distance it was great. This is with a dust sheet too.

Nathan used a laptop with the equivelent of a line-tripled image. I don't have a scaler yet and will look out for a quadscan-pro second-hand.

We also think there is a way to use a 10ft pull down screen in front of the window.

Mark.

 

I must admit that this picture was huge, and did look very nice at a 20ft viewing distance, considering the screen surface.

There was some extra excitement knowing that the picture was taller than the average bloke.

Could the loss of brightness be aided by a higher gain screen? If so, the only trade off would be?

rgds

Nathan

 

......Hot spotting and a narrower viewing angle.

 

Please excuse my inexperience but what does this mean?

Thanks,

Mark.

 

I keep mentioning that old saying "There is no free lunch". This very much applies to the compromise of using large screens with CRT's. I will not get into using double stacked set-ups to achieve high brightness using the reference 1.3 (Studiotek material from Stewart) as "double stacks" are not really feasable for most of us. The only other way to achieve large image sizes with reasonable brightness is with the use of high gain screens. Of course, as mentioned previously, there are trade offs. High gain screens will bring with them a number of problems. Firstly, hotspotting. This is often thought of by many people as meaning that some areas of the image will look brighter than others. More or less correct. Due to the nature of CRT this brighter area is usually the centre with outer edges appearing duller.
In normal viewing conditions, a small amount of hot-spotting will not be visible in anything other than a full white field test signal. However, as screen gain increases, it will reach a threshhold where it becomes visible in the picture. With the very high gain screens used by some people to achieve gigantic images from CRT, it will look like a spot-light is shining in the middle of the screen and will be very distracting.
There is more to consider. High-gain screens have another potential compromise called "Colour shift". As you might know, screens with increased gain are more sensitive to the angle at which light hits the screen. The problem is that with CRT projectors, the Blue, Green and Red light doesn't come from a single source. So, at any given point on the screen, the angle at which the blue, red and green light hits the screen is different. With low-gain screens, this isn't a problem as the gain vs angle of reflection is fairly flat. With high-gain screens, the higher the gain, the more peaky the gain curve, and thus the more variation in luminence with angle. Put simply, what this means, is that the side of the screen closest to the blue gun will be a bit bluer and the side closest to the red gun, will be a bit redder.

I'm afraid I've got a slightly one track mind when it comes to screens. My opinion is that if one has the budget, there is only one screen material to buy. The Stewart Studiotek 130. This was designed to minimise the problems I've mentioned while at the same time giving the most beautiful colours, contrast hence 3D like images available today.

My advice to anyone wanting an extra large image is to make sure they have a well set up, scaled image, and simply move your chair closer.

 

Good wise words Uncle Eric.
I think an 801 would struggle at 10ft wide.
7ft would be more like it.
There are no wrongs and rights if it works for you then fine you are the only one who needs to be satisfied.

(still looking for somewhere to do a double stack install though)

 

That is soooo true!

I've been playing around with the brightness and contrast settings on my pj - I can set them perfectly by the book but as I don't like the result, I ended up just setting them the way I like it. Theres folks that will argue 'til the cows come home about this but it boils down to what YOU are happy with, not what other folks think may or may not be necessary (some things are critical though for decent pq and a 10ft wide picture is a bit much I agree).

But hey, if you want a 10ft picture then go for it! For me, 8ft wide for my 801s (but then again i'm thinking of the future when I'll have a pj with more ummph!).
Paul

 

The main thing for me is that this is a temporary PJ, I intend to get a 9" model when I can afford it. Because I want to run cables under floors I have to decide now where the PJ will sit. The picture is good 10ft wide when viewed from the 20ft viewing position and will be better still when a better PJ is installed.

Uncle Eric's idea of simply moving the chair closer does have some merits but it feels a bit weird to be bunched up at the end of this 42ft room. I'm trying to make the whole space a home-theatre.

10ft isn't set in stone yet, I'll review my final choices when I have the walls painted/blinds in etc.

Mark.

 

42ft room That is BIG! That is definately 9" territory, one of these monsters could disappear in there and easily do the biz on 10ft screen - get saving now!
Regards,
Paul

 

Roland Siad:-

Having had a major session moving between 10ft and 7ft (thanks for your time Nathan) I have to say that a good picture at 10ft the image at 7ft is so much better that I've decided that a 10ft screen should be added later at the same time as a 9" PJ.

Star Wars - Phantom Menance looked possitively 3D at 7ft and we were projecting onto a 7ft bit of white hardboard ripped out of the back of an old wardrobe.

Bearing in mind I'm now at 7ft width. What gain screen material would be sensible?

Thanks for your help in this thread, I could easily have jumped straight in for 10ft and ended up disappointed a few weeks down the road.

Mark.

 

because you are floor mounting you can get away with very slightly higher than the "i've banged my head on it again". I would look at up to 1.8 gain but to be honest I have set up 801s projectors on walls painted matt white and been surprised by the effect.

the best average seems to be between 1.2 and 1.5. but these are figures just quoted about unless you are buying from a manufacturer who knows how to measure these take the measurements with a pinch of salt.

I'll put the 10ft screen back on the self agian then!!!!!

 

Hi Roland

I guess so yes, not suitable for me sorry! As I said in our phone call I needed to make sure that 10ft was doing the right thing and that 4:3 screen wasn't ideal for me...and then there was the advice in this thread from I guy called Roland telling me 7ft was a more sensible size to consider too.

The best thing about 7ft is that it'll fit under the window which solves a lot of problems.

Oh well!, maybe later when I go 9"?

Mark.

 

I just calculated that I could have a 2ft wide picture if put my screen UNDER the window.

 

Roland,
And by my reckoning your PJ should be moved to within around 3ft of your screen. You will need something with a gain of around 0.000001 to avoid colour shift. Nice bright picture though

 

Be just like watching in 3D!