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Projector throw - How far away does the screen need to be?

Discussion in 'Projectors' started by Cobalt, Jan 18, 2009.

  1. Cobalt

    Cobalt Member

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    Hi all,

    I'm sure this question has been asked before though I've scouted a few pages back and not got what I'm looking for, so here goes...

    How much distance do you need between the projector and the screen? I know it will vary between projectors, depend on things like zoom and so forth, but I'm looking for a ballpark figure. I like the idea of having a screen on my living room wall and mounting a projector either on the wall or ceiling opposite but I've only got around 3m to play with so probably only around 2.5m between a projector and the actual screen. The room is about 3 x 6m but unfortunately the ends furthest apart both have large windows in them so using those walls is out the question.

    We use projectors at work and can usually get away with two or three metres though the image quality isn't fantastic though how much of that is to do with a cheap projector I'm not sure.

    Any advice would be welcome - I know plenty when it comes to computers but hooking them up to a big screen and surround sound isn't anything I've done before so any advice is welcome.

    Also, how much would I need to spend? I'm on a fairly tight budget so I can't afford anything in the four figure range but I would like to get the ball rolling so to speak and I think going with a projector over a bigger TV would be a step in the right direction.

    Cheers for any advice,
    John
  2. Big_Si_Owen

    Big_Si_Owen Member

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  3. dovercat

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    I think you would be better off using the longest axis of the room, projectors can be ceiling mounted or put on a table. The screen could be ceiling mounted pull down, some people use window blinds or a portable screen.

    But going with only a 2.5mtr throw distance.

    Using a typical low cost projector that a lot of people seem to like as an example the Infocus X9 DLP costs around £500 probably get it for less, and it is not the cheapest. Note this is just a example not a recommendation, there are many projectors to choose from. For a screen many people just make a DIY screen or project on to a wall. If making a diy screen by painting a wall, a matt white screen is more forgiving of uneven screen surface than a grey screen, the darker the screen the less forgiving, more obvious any uneveness in the surface.

    Throw ratio for this projector is 1.55 to 1.77. You devide the distance to the projector by the throw ratio to get the screen width (note projectors use screen width not diagonal) so: 2.5mtrs devided by 1.55 to 1.77 equals 161cm to 141cm screen width depending on the lens zoom you use. I think there are some ultra short throw projectors that may suit you better than normal short throw projectors like the X9. Some I believe are as low as 1:1 giving you a 2.5mtr wide image at 2.5mtrs. But be aware that the reason regular short throw projectors are usually just over 1.5 throw ratio, is because recommended viewing distance is around 1.5x screen width. At closer viewing distances screen door effect - intrusively visible pixel structure may make the image unwatchable, so you may want to view before you buy.

    When you look at projectors also check offset. DLP projectors are very limited in their placement and some have large offsets. LCD projectors usually have a lot more placement flexiblity.


    In a dark room you want around 12ft lamberts, some people prefer up to 20ft lamberts, others are happy with 8ft lamberts (a crt tv is around 35ft lamberts). Too bright with DLP projectors is likely to induce the dlp rainbow effect and may make the projector unusable. Some people are more sensitive to dlp rainbows than others. Lcd does not suffer negative effects from being too bright.

    Projector Lumens devided by screen size in square feet, multipled by screen gain (matt white is 1) equals ft lamberts.

    The Infocus X9 has 1800 Lumens in bright mode, I would recommend treating manufactures quoted lumens as 50% less since you will probably want to use a projector in low lamp mode for longer lamp life, calibrate the image for best picture quality, and lamps dim as they age. 900 devided by 15.49sq ft (a 161cm wide 16x9 screen) = 58ft lamberts

    At 58ft lamberts you would probably want (likely need with a dlp like the X9) a Neutral Density Filter or/and a low gain grey screen to reduce brightness. A low gain greyscreen will also help reduce unwanted light reflections from light coloured ceiling and walls. While a ND filter can easily be removed as the lamp dims. A ND2 filter halfs brightness (perceived as a 20% drop due to the way eyes-brains work) a ND4 filter reduces brightness to one quarter (perceived as about a 50% drop), low gain grey screens usually only reduce brightness by 20%. So with a dlp at 58ft lamberts you would probably need a ND4 filter, 58 devided by 4 equals 14.5ft lamberts, so maybe a low gain grey screen as well.


    Contrast ratio you want as high as you can get. DLP traditionally has better contrast than LCD which usually relys on a dynamic iris. To benefit fully from high contrast you need no ambient light for on/off contrast, and no reflected light from white ceiling and light coloured walls for ansi contrast. Most of the benefit to ansi contrast can be had by darkening 4 to 6ft of the side walls and ideally the ceiling next to the screen.


    Colour wheel used only in DLP projectors, look for one as fast as you can get to reduce rainbow effect. Colour wheel segments you probably do not want a white(clear) segment they increase brightness at the expense of colour saturation.


    Keep in mind projector warranty type and duration for peace of mind.

    Lamp warranty. Lamp average life and replacement cost.
    Be aware that quoted lamp life is for half of lamps still working with at least half of original brightness, and is based on you using the projector for 2hrs+ a time, and when you turn it off letting it cool down fully before turning it back on.


    Your main problem with a 2.5mtr throw distance will be the distance causing you to have a relatively small and hence very bright image and a very close viewing distance. I prefer the image quality of dlp but you may want to go with lcd as they have more placement flexibility and no dlp rainbow effect with too bright an image. However the pixel structure on LCD used to be more visible than with DLP and could be intrusive at close viewing distances, I do not know if this is still an issue.
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    Last edited by a moderator: Jan 19, 2009
  4. jacko5

    jacko5 Member

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    I have windows either end of my through lounge and I use a pull down screen in front of floor to ceiling velour curtains which pass no light through. using the longer aspect of the room gives you more flexibility in the choice and set up of your PJ and seating.
  5. Cobalt

    Cobalt Member

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    Thanks for the input - I'll have another look and see how much money I'm talking and whether it would be worth turning the room round as it were to use a screen in front of the window.

    Are there any recommendations on budget projectors? I'd like decent picture quality but I'm not enough of a fanatic to want anything top of the line - The ones we use at work are alright as data projectors though they aren't as good when it comes to showing films so I wondered if there was any model or even brans which are worth looking into first.

    Reviews always seem to be so subjective on comparison websites - One person could love a model and think it's the best thing since sliced bread then the next guy claims its rubbish :confused:

    The main thing I want is a decent warranty and reasonably affordable bulbs - Again to use work as an example, we often find it's much cheaper to chuck a projector than to replace its bulb which is something I don't really want to be doing every couple of years.

    Thanks again for the help so far, you've been brill :thumbsup:
  6. Seraphim

    Seraphim Member

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    Hi, I'm thinking of buying a projector and have found this site very interesting. The link below takes you directly to the review of the model which I think is the equivalent of the Infocus IN80. Lots of other models also reviewed.

    InFocus X10 1080p Home Projector Review: Overview
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