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June 17, 2009

4

Multi-Touch Table – Projector Selection

Selecting a projector for a project like this isn’t as easy as it might seem.  There’s a huge selection of choices available and price certainly plays a factor when trying to decide between them.  One of the key requirements for a projector going into a multi-touch table is the throw length and in this case length really does matter.

While I am waiting for some other pieces to arrive I decided to try and find a suitable projector for this project.  I really need to come up with a name for this, “project” isn’t very cool sounding.  As previously stated one of the key factors when looking for a projector to go inside a table is the throw length.  Specifically you want a projector with as short a throw length as you can get.  A projector with a short throw length will create a larger image at a given distance than a projector with a longer throw length.  There are “short throw” projectors available but they typically involve complex optics and have correspondingly high prices.  They can also complicate your table design since the steep throw angle often (but not always) requires placing the projector in such a way that it requires significantly more space on one side of your design than the other.  With all of this in mind I set out to find the best projector for my table – that I could reasonably afford.

Requirements

Before you get into this too deeply there’s a few key things you need to know:

  • What is your desired screen size – how big do you want your projected image to be?
  • What is your desired enclosure size – how big do you want your table to be?
  • What resolution and aspect ratio are you planning to run your table at – 800×600?  1024×768? 1920×1080?!
  • What environmental conditions will you be using the table in – Dark room?  Full sunlight?  Something in between?
  • Your budget – how much can you spend?

Once you have answers to those items you’re ready to go.  In my case, I’d like a roughly 45″ diagonal screen size at either a 16:9 or 16:10 aspect ratio.  This amounts to an image about 25″ high and 38″ wide (slightly different depending on which aspect ratio).  Because of the aspect ratio I want I am looking for a projector with 1280×800 or 1280×768 resolution.  I had initially hoped for a 1080P resolution but then reality hit (see the budget part).  As for the enclosure, I don’t want my table to be more than 30″ high which is typical desk/table height (between 28-30″) and I don’t want it to be more than about 34″ wide – since it won’t fit through the doorways/stairways in my house if it’s wider.  I imagine the table will be roughly 50″ long but that doesn’t really factor in here – the key dimensions here are the height and width.  I also want the table to be usable in fully lit rooms, perhaps not full sunlight (that causes it’s own issues with IR tracking) but certainly partially sunlit rooms are on the list for me.  My budget for the projector is $500 – which is , as I quickly realized, too low.  More on that later.

Projector Resources

Now that I had some parameters to work with I set about finding suitable models.  A couple of great resources for this are:

http://www.projectorcentral.com

and

http://www.aboutprojectors.com

Between them they cover a huge range of manufacturers and models and give pretty detailed specs on all of them.

Reality Strikes

I spent about 2 days combing through looking for projectors matching the specs I wanted.  Once I had the list narrowed down a few things became apparent – my budget was woefully small, and nothing even within the realm of twice my budget was going to get me the screen size I wanted within the size contraints of my enclosure.  The first of these issues was addressed by setting my budgetary expectations to a more realistic level.  While there are several 800×600 and even a few 1024×768 projectors around that can be had for just over or around $500, there are not many 1280×800 projectors that can.  While there are many 1280×800 projectors that list under or near $1000, none of them are true “short throw” projectors – those list for somewhere around $1500-$3500.  Projector brightness or lumens is also a factor here.  Some projectors output 1200-1600 lumens – this is still really bright, but maybe not bright enough for full daylight viewing or when paired with high contrast projection materials.  I wanted something with 2000+ lumens.  This, also, means more money.

The obvious first step after this dose of reality is to think “well, maybe I can find a used projector and save some money – I’ll hit my budgest that way”.  And that seems perfectly reasonable.  The problem with that idea at the level of projector I am buying is that replacement bulbs cost 1/3 – 2/3 the price of the whole projector.  So if I were to find a $1000 projector for $500, but had to buy a replacement bulb (within a few weeks or even months), I might end up paying $800 in the end (bulbs typically range between $200-$300).  At that point I’d be better off just springing for the new model, getting a warranty, and knowing the bulb should last a good, long time.  So I upped the budget to $800-900.  Really only two projectors made this cut (though there are lots of projectors in the range of $800-$1200).  The first is the Dell 1609WX, the second was the Epson PowerLite Home Cinema 700 (hereafter known as “The Epson”).  The list prices for these are $849 and $799 respectively.  Features and specs are very similar with a few differences – here’s a comparison.

Final Evaluation

Here’s how I made my selection-

  1. Price – the Dell lists and pretty much sells for $849.  The Epson lists for $799, but sells for as low as $749.  Advantage Epson.
  2. Throw distance – The Epson throw ratio is at 1.5, the Dell, 1.55 (smaller is better).  The Epson has a better zoom.  The difference in throw distance for the screen size I want ends up being about 3″.  That seems insignificant but as you’ll see later, every inch counts.  Advantage Epson.
  3. Display Technology – The Dell is DLP, the Epson is LCD.  Most would say DLP gives a better picture with greater contrast, and it’s probably true, but the rated contrast gives the edge to the Epson (but never trust those numbers folks!) so how to decide?  In this case, because of the potential for strange mounting orientations LCD is a safer bet.  DLP has moving parts and they are engineered to work properly witht he projector sitting on a table, or hanging from the ceiling – both cases projecting horizontally.  In my case I may need to mount the projector vertically and that means possible issues with the DLP color wheel.  Advantage Epson.
  4. Size and weight – the smaller it is, the easier to mount/position.  The Dell wins here but the margin is slim, still, inches count.  Advantage Dell.
  5. Brightness – The Dell is rated at 2500 lumens, the Epson, 2000.  Since both meet my requirement of at least 2000 I needed to look a little deeper.  Heat is going to be a concern in this box and honestly 2000 lumens might be overkill anyway.  In most cases the Epson should run cooler since it should have a less powerful lamp = less power draw = less waste heat.  Advantage (conditionally) Epson.
  6. Connectivity – This is pretty much a wash as all I cared about was a digital video input but since the Epson supports HDMI it does reduce the total number of cables required if I decide to use the projectors speaker (and I probably will), it’s smaller physically than a DVI connector and easier/cheaper to find right-angle connectors for.  Advantage Epson.

All in all, the Epson solidly wins.  So now I have a projector.  There’s only one problem…  To get the screen size I want requires 56″ inches of throw and I have a box no more than 30″ tall.  Fun.

Tune in next time for the answer of how to fit 56″ of crap in a 30″ box.

Remus out.

Read more from Multi-Touch
4 Comments Post a comment
  1. Mitch
    Jun 2 2010

    This is fantastic, it was just the information I was looking for.
    I’ll probably have more room for throw than you will; is a short throw a costly specification? Will it be easier to find (and cheaper) monitors with that have a more common long throw and a higher resolutions?

    Reply
  2. RexRemus
    Jun 3 2010

    @Mitch
    Mitch-

    Short throw projectors are pretty much always more expensive because of the complex optics that go into creating that short throw. So yeah, it’s cheaper to get a longer throw projector but there’s a catch here – with a longer throw you’re going to need to fold the projection (unless you are building a pub-height table!) and that means getting first surface mirrors and even the cheap ones can be pretty pricey. If you need to do a 2 mirror bounce it’s even more costly. There’s also an investment in time. In the end it might be cheaper to get the short throw and avoid the rest but it’s going to vary by use case. You really need to run down your design and understand the trade-offs between solutions.

    Reply
  3. Mitch
    Jun 4 2010

    @RexRemus
    Remus, thanks for the reply.
    How do you account for distortions when using the mirrors? Won’t they change the way the projector hits the acrylic surface?
    I’m researching this in the hopes of building more of a aisle surface than a desktop, so I have a pretty good deal of flexibility in setting up the projector, but I’m unsure of the effects of using a longer throw distance on the resolution, perspective distortions caused by bouncing the projection off of mirrors, etc.

    Reply
  4. RexRemus
    Jun 4 2010

    @Mitch
    Configuring a folded projection is as much art as it is science but it can be done. In fact it’s done quite often in rear projection scenarios. Here’s a good/quick writeup about it: http://www.da-lite.com/education/angles_of_view.php?action=details&issueid=28

    Basically you don’t need to worry about getting a non-distorted image but you DO need to worry about calculating the math involved in the proper projector/mirror placement to get that undistorted image. Setting it up is not easy or fun. Like I said earlier sometimes the cost of a short throw projector can outweigh the cost in materials and TIME for trying to fold a longer throw.

    Reply

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