Click to enlarge. SO close
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Of important note, the HD73 offers two digital inputs, a real plus for many users. Of course if you do plan to also hook up your computer, you will need the DVI-I for that. Note, you can buy a HDMI or DVI switch box, but they tend to cost about $250 or more at this time.
The HD72 vents hot air straight out the left side of the projector from vents mounted near the rear. Theoretically you could mount the projector on a rear shelf, but two things make that unlikely: First, the limited range of the zoom, makes it unlikely that most people will find that they can position the projector on a rear shelf in most rooms. Secondly, even if the distance works, the projector needs to be positioned below the bottom of the screen, or above the top of the screen. Below the bottom, shooting across the entire length of the room from a low angle probably won't work, with couches, chairs, etc. being in the way. Mounting up high, would require the projector to be inverted (as with a ceiling mount). That means either putting up a shelf and mounting below it, or building a cradle. If were to build a cradle, it would be extremely important to make sure you compensate for the lost ventilation. As I said, not very practical.
Time to get to the "good stuff" - the Optoma HD73 DLP home theater projectors image quality.