user2504: I have a few small projectors for small rooms, but I'm finding that these do not work well for pushing light to a larger screen further from the point of projection. 
In looking for possible upgrades, what key features do I need to evaluate in comparative shopping?  Is there a metric or feature I need to look for in a projector that will allow it to throw a bright, clear video projection from further away?  To clarify, I'm not needing to replicate what the local cinema's use - I'm only showing slides not video content.  

user2836: The lumens of the projector is the primary indicator of how bright it is.  Contrast ratio is also significant for determining how dark the dark pixels will be when bright pixels are bright, but a lot of that also depends on the type of screen you are using.
The size a projector can project is determined by the overall amount of light it can throw.  As surface area increases, the amount of light that reaches it goes down according to the inverse square law.
This inherently makes sense when you think about it for a minute since you have a fixed amount of light coming out of the projector, but the larger the area you are trying to cover, the less light you have to cover it with per inch.

user5074: You'd probably want to look for the following characteristics:

Min and max projection distance (from the data sheet, make sure the projector can focus correctly for the desired distance)
Lumen (some people recommend 500 lumen per square meter projection area, but of course, this also depends on your ambient lighting)
Native image resolution (projecting on a large area the image may become blurry with low resolution)
Diagonal image size (make sure the resulting image size fits your intended projection area)


2504: <p>I have a few small projectors for small rooms, but I'm finding that these do not work well for pushing light to a larger screen further from the point of projection. </p>

<p>In looking for possible upgrades, what key features do I need to evaluate in comparative shopping?  Is there a metric or feature I need to look for in a projector that will allow it to throw a bright, clear video projection from further away?  To clarify, I'm not needing to replicate what the local cinema's use - I'm only showing slides not video content.  </p>
 2836: <p>The lumens of the projector is the primary indicator of how bright it is.  Contrast ratio is also significant for determining how dark the dark pixels will be when bright pixels are bright, but a lot of that also depends on the type of screen you are using.</p>

<p>The size a projector can project is determined by the overall amount of light it can throw.  As surface area increases, the amount of light that reaches it goes down according to the <a href="http://en.wikipedia.org/wiki/Inverse-square_law" rel="nofollow">inverse square law</a>.</p>

<p>This inherently makes sense when you think about it for a minute since you have a fixed amount of light coming out of the projector, but the larger the area you are trying to cover, the less light you have to cover it with per inch.</p>
 5074: <p>You'd probably want to look for the following characteristics:</p>

<ul>
<li>Min and max projection distance (from the data sheet, make sure the projector can focus correctly for the desired distance)</li>
<li>Lumen (some people recommend 500 lumen per square meter projection area, but of course, this also depends on your ambient lighting)</li>
<li>Native image resolution (projecting on a large area the image may become blurry with low resolution)</li>
<li>Diagonal image size (make sure the resulting image size fits your intended projection area)</li>
</ul>
