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Help required selecting the best DIY screen for a DIY LCD projector

Discussion in 'Projectors, Screens & Video Processors' started by NathanLance, Apr 29, 2005.

  1. NathanLance

    NathanLance
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    Hello all,

    I recently completed my DIY projector, which uses the old 'placing an LCD screen over an overhead projector' method.

    I am massively chuffed with it (especially with total cost < £150), but now I need to build myself a decent screen so I can get the best results. At the moment I am just using a white bed sheet that I have hung up.

    The OHP is 4,500 lumens output, and the LCD monitor has a 450:1 contrast ratio. From what I can gather this means I should go for a grey shade screen, so I can gain more contrast by sacrificing some brightness. Indeed, when I judge the image quality by eye, it seems that the main problems are that sometimes the whites are too white (like a saturation type effect), and the blacks/dark colours could do with being darker. Overall the colours could be more 'punchy', they appear a little washed out. In addition there is a huge amount of 'backwash' - even with the OHP being the only light source in the room, there is still a lot of ambient light - easily enough to read a book by without straining your eyes for example.

    I've arrived at these forums during my search for advice on building your own projector screens and it's been very interesting to read the huge amount of info here!

    My current plan is to build a wooden frame, stretch some sort of material over it, then paint that with this icestorm 5 or 6 that everyone seems to go on about :) Does this seem like a good choice?

    Thanks all,

    Nathan
     
  2. sploo

    sploo
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    Hi,

    I've done basically the same (with a similar power OHP), but a lower quality monitor. See:

    http://spikyfish.com/1.jpg
    http://spikyfish.com/2.jpg
    http://spikyfish.com/3.jpg

    I got a cheap (<100GBP) screen that's almost certainly intended for office presentations, rather than a special cinema screen.

    I do find that contrast is an issue - anything dark grey and below is just a mess of dark grey. I've tried flipping the screen over (white on one side and black on the other) and it's arguably better for dark films, but I generally prefer the white side.

    I run the OHP on a reduced power mode as I also find it's full power is too much. It's worth it though, as it apparently increases the bulb life.

    I'd strongly recommend just getting a cheap white screen - or maybe a white/light grey unit, as the picture from these homemade units is good - but doesn't justify a fancy screen.

    BTW You've probably noticed from the pics that I've made cabinet for the OHP & PC. It's very good - as you get almost no light pollution. In any case however, I'd strongly recommend you keep an eye on LCD temperature - I'm running two 120mm PC fans, with a homemade vent, which directs air onto the LCD panel - otherwise it gets *very* warm.
     
  3. PJTX100

    PJTX100
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    Ingenious idea, less discrete than a PJ but sploo's pics look very impressive.

    Depending on the material it may sag or not take the paint very well. If you are going to paint then perhaps MDF or hardboard may be a better idea...PJ
     
  4. NathanLance

    NathanLance
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    Sploo,

    Thanks for posting those pics, it's really interesting to see how someone else has fared with their DIY projector. You seem to have a very nice setup there.
    I spent last night building a cardboard housing for the projector to prevent all the uneccesary light leakage, and it did make quite a difference - I was very pleased. The ambient light in the room was a lot lower, and the picture had more contrast and was a lot more striking. (However, the projector does look like sh*te - not that _I_ care, but it's not as impressive to the women to have some carboard monstrosity sat in the middle of the room). I wanted to ask, did you build your cabinet from scratch, or did you buy one from somewhere and then adapt it? Where have you placed your fans? (I assume at least one blows between the LCD and the OHP - do you have a fan that blows into/out of the cabinet also?). As a side point - I can run my projector with no fans on it (other than the internal OHP fan) and the LCD screen doesn't overheat. How does yours fare in this respect? (I'm thinking about before you put it in the cabinet).

    Also, I find the next 'thing' on the list I need to fix (besides sorting out a better screen) is the noise that the OHP makes - caused by the internal OHP fan. Did you experience any problems with this? I find mine can cause the OHP to vibrate at times. I assume your cabinet also reduces the perceived fan noise?


    PJTX1000,

    The reason why I suggested the material approach instead of simply painting an MDF board is because I'm a student and thus move accommodation relatively often. I want my screen to be at least 6 foot square (it has to have a 4:3 ratio because I also use my projector for playing games on, and the screen has to be free-standing - i.e. I can move it around, and it stands on the ground), and I don't have the means to transport a board of wood that size every time I have to move! So I need a screen I can dismantle really. I would prefer to have a solid board though - I was thinking about perhaps buying two 6' by 3' boards, and then joining them together somehow. The problem then of course is joining them together without making a visible seam. If I was only to project on one side, I guess I could screw them together on the back side, perhaps use some kind of tape to go over the seam on the front side, and then paint it. BUT, ideally, what I want to do is use both sides of the board. One side for 16:9 viewing (films), the other for 4:3 (games). I was going to put some black velvet borders on each side you see, to make the 16:9 and 4:3 ratios. Then I can just flip the board around depending on what I want to use the projector for. So that means I can't join them together with anything visible. I'm assuming glue will not be strong enough?

    And here is another little problem I could do with some ideas for: Ideally, I want the screen to lean forwards a bit. There are two reasons for this:

    1 - the way the OHP projects means that the bottom of the image is wider than the top, I believe the tilt of the screen would correct this.
    2 - I watch my films lying on my bed, which is directly in front of the screen, so it would be nice for the screen to be angled downwards to face where my head is.

    I'm thinking of an angle around 10° - 15°. The difficulty is that I can't attach it to anything on the walls/ceiling. I guess I have to make some sort of mount that it sits on.

    hmmmm....

    Nathan
     
  5. sploo

    sploo
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    You're not wrong about it being less than perfect on the aesthetic scale! Even my old man, who normally coughs up a lung at spending money, took one look at the 'fridge' and said "I think you need to buy a projector!" :)

    When I first got the OHP and LCD screen, I built a simple box with a recessed top lip, and no bottom. The LCD fit on top, and the whole thing went on top of the OHP (the screen being about 5cm above the OHP fresnel glass).

    Big problems - the light power increases significantly as it's focused in towards the lens, and the LCD was discolouring in the center due to heat build up.

    I built a second box, which mounted the LCD about 0.5cm above the OHP, and had two small fans dragging air between the LCD and OHP glass (powered off the LCD circuit board 12v output that was used for the LCD backlight).

    The worked OK, but was still pretty warm, and, as you've found, suffers from light pollution issues.

    So, I build a cabinet from MDF - bottom, sides, back, and an open front, closed with a door using standard kitchen hinges.

    Inside is a shelf to put the OHP (or more specifically the center of the OHP mirror) at the right height for the screen.

    I made the cabinet as short as possible, so there's a chunk removed from the back wall for light to pass, and the lid is a flat piece of MDF with a raised section for the OHP head (see the pics I'd linked).

    Also in the cabinet are a PC and a PS2 (the PS2 going into a TV input card in the PC).

    This works well, and the cabinet makes the system much quieter, but I was still having significant heat problems on the LCD.

    I removed the lid, cut two 110mm diameter holes, and mounted two 120mm fans, powered from the PC (with a resistor pack to quieten them down slightly). You can just see the fan grilles on the third picture.

    On the underside of the lid there's now a cardboard duct to ensure the air is blown down at an angle onto the LCD (and should rise up out of the back of the cabinet - through the hole facing the projector screen).

    I was still having problems with the OHP getting hot, so I cut some grilles into the side of cabinet, and that improved things (the OHP drags air in on one side and expels it out the other).

    Unfortunately, I'm now finding (due to warmer weather) that the PC is having problems, so I may need some more mods to keep it cool. I always had problems with the PS2, so I just lift it out and close the door when playing.

    I guess the whole cabinet probably needs to be water cooled (for efficiency and low noise), but you'd still probably need a fan for the LCD, and for the cost you might as well buy a proper projector!
     

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