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Newbie, Gain, ambiant light, HELP !!

Hi, hope you can all help me :)

Ive got an Infocus x2 running on eco mode.
At the moment I am throwing straight onto my wall, My wall is a biscuit colour and the wllpaper is blown vinly with a "canvas" affect design.
Im fairly happy with the picture I produce like this, but the colours are not great.

Im thinking about buying a screen, I have a couple of options.
My problem is I dont know much about 'gain'.

My front room has a white celieng and a dark red carpet, I cant control the ambiant light during the day that well, excepy by closing curtains ect.
If I want to use the pj in day time, I switch the pj to full power instead of eco, and the picture is ok ish. I use the screen more at night than day time though.

Would it be beeter to by a high gain screen? Ive been offered a Da-lite screen with a gain if 2.8 , would this be suitable to use my screen in the day time on eco mode? as well as using at night time?

Or am I better of with a screen gain of 1?
Is it worth buying one of the budget screens of ebay with a gain factor of 1?
I have about £180-£130 to spend on a screen, I know its not a lot, but there are a few deals out there for a second hand screen, or like I said a budget new screen from ebay.
The screen size I need is between 80" - 100".

Please help :thumbsup::thumbsup:
 

martin purnell

Active Member
Hi,
You could always make a screen or repaint the wall with professional paint such as Goo for around £200 or your own blend for around £25.
Worth reading up on threads entitled Paints Brews and Mixes 2 which will give you all the info needed. As soon as someone tells me how to download my pics then I can finish off Paints Brews and Mixes 3 which will show a completed screen with the "proper custom made blended paint courtesy of 2 paint Companies!"
Re ambiant light, I am assuming that your curtains have blackout linings? These are different to the ordinary "petticoat type material" you see on most curtains. They are readily available and ready made to fit whatever size curtains. They are not expensive either and hang with existing curtains.
Re buying on Ebay. There are threads already within this section that covers the pros and cons.
Hope this helps,

Martin
 

Fred Flintstone4

Active Member
"Gain" is the phenomenon associated with front and rear projection screens. What it's describing is the apparent increase in brightness. From this you might think that the screen is actually amplifying the brightness but this would be incorrect. The screen is returning the illuminance of the projector back into a slightly tighter viewing angle than what would be returned from say, a wall painted white. A good analogy is a 12 volt bulb. Connect it to a 12 volt battery put it in front of the white wall and the brightness on a dark night is OK. Put that bulb in front of a parabolic reflector as found in a car headlight and the same light bulb would light up bends in the road over 300 metres away. The bulb is still the same brightness but that brightness is being used in a much more efficient manner. All the brightness is concentrated into a really tight angle. If you were to stand on one side of the headlight it would not seem that bright but if you were in a car coming toward the headlight then you would know about it!

When applied to a projection screen the analogy is still pertinent. Do you remember the early 3 tube CRT projectors often seen in pubs? These had a silver parabolic screen, just like the car headlight. Nice and bright when you were stood in the right position (the "on axis" or "0 degree" position) but not very bright if you were off to one side.

So a screen that is incredibly bright has mistakenly (my opinion) been called a "high gain" screen when in actual fact I think it should be a "low loss" screen. But I think "high gain" sells better than something that has "loss" in its name...

How do we quantify this gain? Like anything else we use a yardstick or a reference point.

The reference from which "gain" is measured is magnesium carbonate (I have a block on my bookshelf). This is known as "unity gain" or a gain of 1. Gains of significantly greater than 1 are called "high gain" (nobody has quantified where gain becomes high gain...) and those less than 1 sometimes "low gain".

A really high gain screen was the silver parabolic one I saw 20 years ago. It had a gain of 16. 16 times brighter than a wall painted white! The viewing angle was about 5 degrees horizontal. It was only any good for one person sitting in one position and so was probably used for a flying simulator. For a lower gain figure you get a wider viewing angle - you can have friends round and they don't have to sit on your knee to see the picture (this may or may not be a blessing in disguise). If you come down in your expectations of gain numbers then you can have a gain of 2.8 by using a material called High Power. This has an on axis gain of 2.8 when compared to the magnesium carbonate. This apparent "gain" in picture brightness is wonderful if you need help with brightness. My Barco has wonderful resolution and black levels but it's not very bright so a High Power screen with a gain of 2.8 helps enormously. High Power has glass beads in its construction (but it's smooth to the touch and very easy to clean) and is also retro reflective. This means that the brightness will go back to the light source. If you want a good example of this effect then look at a hi-vis jacket worn by the motorway police and other people requiring high visibility. At night when you're driving toward them with your headlights on you can see them clearly. If you were to stand next to them while somebody else was driving toward them then you think that the stripes in the jacket were not that bright - the brightness is being reflected back into the eyes of the driver of the oncoming car. Below High Power in the gain levels there is ordinary glass beaded material. This feels like sandpaper to the touch and has a gain of 2.5. It's difficult to clean and the glass beads sometimes fall off over a period of time. You might think that it's a good idea to get a bright projector then run it on a high gain glass beaded screen. Brightness is not the answer. Just turn the brightness up on your old fashioned television and see what the picture looks like. What you really want from a picture is contrast.

There are other materials that have a high (higher than 1...) gain that are not retro reflective. They are sometimes silver in appearance. Depending on your age, you may have heard of the saying "star of the silver screen". This harks back to the days when the projectors in cinemas were not that good and the screens were made from a silver material to enhance the brightness. There are silver screens in gains of 2 downwards. As the gain figure goes down the viewing angle increases.

When I started in projection over 20 years ago the projectors were not that bright. We had a laser video projector which would produce 270 lumens. We could only do pictures 30 feet wide... This was on standard cinema screens!!! Today's projectors will produce 8 - 10 times that figure and the screens are a quarter of the area so naturally the picture has a lot more punch to it. A Toshiba projector which I took to my local cinema (now closed, unfortunately) had 800 ANSI lumens. This produced a 16 feet wide picture which was deemed sufficiently bright enough for public consumption.

Consequently, I think that modern LCD/DLP projectors don't really need any help with the brightness. A projector producing 1,000 ANSI lumens on a 106" diagonal 16:9 screen of matte white with a "gain" of 1 produces a picture that's twice as bright as the minimum once required by SMPTE. The projectors are now so bright that they need the brightness reducing. You can buy "filters" which you put in the lens system, you can use "grey" screens. Grey screens can sometimes be recognised by the fact that their screen gain is less than 0.

Why buy a projector so bright it needs artificially reducing? Would you buy a Ferrari then tie it to a concrete block to slow it down? The grey screen is used to enhance black levels. This is slightly different to the projector brightness thing. You may have a lot of ambient light in the room which needs toning down and sometimes this can sometimes be achieved by using a grey surface. The only problem, I am told, is that the whole picture becomes greyer. This will become more noticeable as the projector lamp gets older. Some projectors lose half their brightness over 500 hours.

So, there you have it in a nutshell... The easiest solution for today's average LCD/DLP projector is to go for a Matte White screen and run the projector in economy mode with as little as possible ambient light falling on the screen. You may not have heard of Grandview but they make screens for a few so called "manufacturers"!
 

Peter Parker

Distinguished Member
Gain screens can help reduce the effects of ambient light since the gain reflects the light back to the source or viewer (depending on being angular or retro reflective) more than a screen without gain will (which reflects it equally everywhere). If it's retro reflective as Walter has excellently explained, it will send the light pretty much back to the source, so any ambient light coming onto that screen will be reflected back where it cam from (i.e the window) and not towards the viewer. The projected image will be sent back more to the pj than other parts of the room. With a retro reflective screen your head needs to be close to the pj for best brightness. A window behind the pj will of course illuminate the screen in a similar fashion to the pj so then the Hi Power may not be such a good choice. You have to try and think what the gain is going to do with all light sources - pj and ambient.

Angular reflective will work in a similar fashion but have their best results with the pj on the ceiling and the viewer sat below. How effective the angular gain is with ambient can depend on where it's coming from in relation to the viewer but the tighter viewing cone can mean the ambient light is not sent to the viewer as much as it will with a unity gain screen since it is confined to a cone as Walter has explained.

Grey screens help by having a darker base so can show better dark detail compared to a white screen in ambient light. The darkest a screen will ever be is how dark the room can allow it to be. If you have a grey screen it will look darker than a white screen in the same conditions (as Walter said, generally they are lower gain), so any ambient light will illuminate the screen, but the lower gain grey screen will look darker than a unity gain white screen. Shine an image onto the grey screen and the dark parts will look darker than the same image on a white screen in the same conditions so will have more visible detail there.

Add an optical coating to a grey screen and you get a great combination for reducing the effects of ambient light. There is a Greywolf screen that works well as it is retroreflective with an advertised gain of 1.8. The drawback is that it has a slightly 'sparkly' look to it due to the glass beading under certain conditions (the Da-Lite High Power doesn't have this as far as I know). Da-Lite do a grey screen with an advertised gain of 1.1 so should still be better than a unity gain white screen in ambient conditions. Do a search for Greywolf and you should find some threads that show how effective the screen is with ambient light.

If you ever see the Stewart split screen demo where they use their Studiotek 1.3 gain material alongside their Firehawk (advertised as 1.3 gain more like 1.15 gain) material in a brightly lit room (the screen is half and half of the two materials), the Firehawk screen has much more detail and is far more watchable than the white screen which looks quite washed out in comparison. Unfortunately the Firehawk is very expensive but grey screens liek the Greywolf are excellent value.

When ambient light isn't a problem and the walls are dark coloured I would concur 100% with Walter and always suggest a white screen, but if you have ambient light or light coloured walls that reflect light from the screen back onto it, a grey screen has its advantages.

Maybe you could use a pull down grey screen for daytime watching, and stick to your wall for night time viewing? You get the best of both worlds then, and the Greywolf is only around £100 for a 92" screen IIRC. Try to demo some screens if you can.

Filters can be a good thing IMHO. If you want an image that is more cinematic and has a reflectance level similar to the cinema but you can't get a big enough screen to achieve that, a bright projector can have its lumens reduced by adding a Neutral Density filter (ND2, ND4 for example). If you want to watch at night when ambient isn't a problem, you can fit the filter for a more cinematic look. If you want to watch when there is ambient light during the day, you can remove the filter to combat it. The other advantage is that as the lamp ages and dims, you can remove the filter to get some lumens back, though of course by that time the ability to combat ambient light has been reduced. A dimmer image isn't to everyones taste though

In an ideal world you can match the pj lumens to the correct size screen so that you have cinema levels of reflectance over a reasonable life span of the lamp, but for various reasons this isn't always possible, so lens filters have their place in home cinema (and colour correction filters can be used to increase contrast in some cases as well, when correctly calibrated, but that's another story).

Grey is simply white at a lower luminance, and with the eye being as adaptable as it is with it's own white balance, grey will look white where you will expect things to be white. Place a piece of white A4 onto the grey screen and the grey screen looks grey again.

Gary
 
Thanks everyone, if i was 2 change my room round and have a screen that comes down infront of my window, what would the best option for a screen? greywold? high gain, or normal?
 

martin purnell

Active Member
Thanks to Gary, Walter and J316 (for starting this thread. I bet you didn't think you'd get the answers that you got!). Gain means even more now.
As someone who went the home built way (I won't bore you with reasons other than pull down screens weren't an option) I must say I've had fun building and reading up on what paints to use! Like most people, money is an option but I can appreciate why good screens cost more esp getting rid of ambiant light.
Whilst it might not be in Walter's best interest to give me advice (because he sells screens! It's great though to know someone in the trade who knows what they're talking about and seems passionate about the subject) there must be some tips I can be given to improve my existing ,ahem, bespoke screen! It has been discussed on Paints, Brews and Mixes II thread. I have just started the sequel (PBandMIII) but until I can download the pics, it is going nowhere fast!
The paint used was Dulux Lumitec Light and Space plus Craig and Rose Sensual Silver metallic paint. The intial mix ratio was Dulux 5 to CandR 1. The latter was used to make the blacks, blacker as the Sanyo Z3 is an LCD pj.
Here is a review of the Dulux paint....

Ground breaking LumiTec™ technology is behind Light & Space, the latest innovation from Dulux Trade. This pioneering new colour range reflects up to twice as much light*, making rooms look and feel more spacious and contributing to potential energy savings.

Light & Space uses cleaner tinting recipes and paint components resulting in surfaces that are more reflective and less absorbent of natural or artificial light. As such, significantly more light is effectively reflected and distributed around a space.

Smaller windows and energy efficient, or lower wattage, light bulbs are increasingly being used throughout building design and fit outs, following demands by Building Regulations Approved Document Part L that as little energy as possible is lost through the building fabric and fittings. However, this does affect the levels of light in a room. Dulux Trade's new Light & Space colour range has been developed to combat this problem.

Tests have shown that when comparing Light & Space with a standard paint of similar hue and chroma it is possible to have up to 20%** smaller windows and yet still achieve the same levels of light within a room. When it comes to distributing artificial light, Light & Space has also been proven to achieve the same average level of illumination, using up to 20%** less lighting energy.


The screen is a perfect 75 inch diagonal widescreen that takes the full screen signal form a DVD via my beloved Sanyo Z3.The lens is on minimum aperture. The centre of the Pj lens is 19" from the ceiling. The centre of the screen is 28" from the ceiling. This means that the Pj light will hit at a slight angle before rebounding to our eye level. We actually sit right underneath the PJ. Despite best efforts on the anti-ambiant light front, some does creep in from the big side window to our left. New curtain track/poles would have to be fitted plus new curtains to remedy this problem.
I took on board the glass beading and what it does.
Apart from stating the obvious as in ....Buy this ready made screen or get new curtain track.....what can I add to the screen to improve the gain and get rid of excess ambiant light? For instance, is there a glass beading liquid solution I can add?
Any thoughts on this would really be welcomed. Thanks again for your excellent responses to Jesuslovesyou's thread. I am not trying to hi-jack it either but embellish it....hopefully for my needs and his!
Kind regards,

Martin
 

Fred Flintstone4

Active Member
Hi Martin, you're right about my interest in screens. A few years ago I tried to get the editors of a few well known high street magazines to publish an article about screens and they weren't interested - they said "Screens are boring!" How wrong can you be?

With regard to glass beads, I don't know of any paint or other treatment for embedding glass beads. I did have a bag of glass beads for an experiment but I couldn't find a safe and sensible way of getting them to stick so I gave up and left it to the material manufacturers.

I see in your post that you mention curtain track. We have been working with a well known manufacturer and using their products for about 20 years and they have a new line in curtain track available. Have a look at the website and see what's available. Sorry, no glass beaded paint...
 

Peter Parker

Distinguished Member
Hi Walter,

I used a basic manually operated chorded curtain track in my last home cinema (currently cinemaless due to house move), but when I get round to doing the next room I may be interested in the remote operated track on your site. My curtains were hand made with a slim pocket down the leading edge and a thin piece of dowel was inserted to give a heard edge against the image, but it sometimes needed manual tweaking for best results (wouldn't always hang straight). How do you ensure a vertically straight hanging edge to your curtains? Is the bottom weighted to some degree?

Gary
 

Fred Flintstone4

Active Member
Ah - a chance for a short answer - with curtains we only supply the track. You supply the curtains!

For your application I would tend to treat them as masks rather than curtains. Masks tend to be almost touching the screen surface. On some multi format screens the masks move to the desired position then swing toward the projection surface and touch the screen. If you use a laser video projector then you can get away with quite a gap between the curtains and the screen but that's another story!
 

Fred Flintstone4

Active Member
Just to get back to JLY's request about a screen. If you want to put a screen in front of a window then there is a possibility of combining a blackout blind with a projection screen. The main material for projection screens is a black backed woven fibreglass which does not allow the transmission of light. At the end of the day it's down to budget...
 

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