I Need Short-Throw Projector Advice

I’ve been using two projectors for a while now, neither are short-throw. Now I want to do a new installation using 2 short-throw projectors. This new project spurred me to really research projector technology for the first time. What I learned is that most projectors in general, especially sub-$2000 short-throw projectors are designed so that the projector will be placed above or below the actual screen. This is called the vertical offset of the projector and each projector has a vertical offset ratio that can be used to determine the offset at a given distance. Adhering to the offset ratio should, in theory, give you the clearest possible projection.

If you checkout Optoma’s distance calculator you’ll see that every Optoma projector is designed to be placed above or below the actual screen.

Interestingly though, I called BenQ and ViewSonic and representatives from both companies could not tell me what were the offset ratios for their projectors.

The really high-end of InFocus projectors allow you to manually adjust the “vertical lens shift” of the projector (which changes the angle of the lens I believe), essentially allowing you to adjust the offset ratio.

Over the phone, an InFocus tech warned that taking a projector without lens shift and angling it with a ceiling mount to essentially lower the offset ratio and using keystone adjustment to make the image square would negatively effect the life of the projector (he didn’t say those dreaded words, “nullify your warranty” but I did get the feeling it was on the tip of his tongue).

The ViewSonic tech I spoke to said I could angle the projector any which way I pleased, no prob, bob.

Anyway, after all this research I realized that I had improperly mounted my Optoma HD20 projector a year ago. Currently the projector sits a good two feet lower than the top edge of the apx 13 ft wide screen. Optoma recommends a 14" offset meaning my projector is mounted a good 3’ from where it should be, ideally. Thing is, I’ve never noticed. The picture looks great. (I believe that in theory an improperly mounted projector should have one edge that is more out-of-focus than the other)

So after all that, my question is… can I cheat with short-throw projectors? Can I mount a projector intended to be 9"-12" inches above the screen 1 or 2 feet below the top edge of the screen? I suspect that long-throw projectors might have more leeway than short-throw in these sort of circumstances. However, can anyone shed any light on this issue who might have experience with short-throw projectors?

This is the projector I’m thinking about doing this with…

( Or… do you know of a sub-$1600 720p short-throw projector that would fit the bill? )

hi gilbi,
i have some experience with the short throws, in particular i have used the benq line of short throws like the BenQ MP772ST, and the hitachi too (more short throw thant the other you saw). http://www.projectorpoint.co.uk/projectors/Hitachi_CP-A100.html
anyway, i’ve used the benq and the hitachi in many installations, sometime using the suggested setting, but sometimes using some strange settings, like the projector in vertical (from top to the floor of a room). I’ve never had problems about that, i think when you project and your eyes see a good result it’s ok.
hope it helps ;)

ps. i know that nec is making some nice short throws, but never tried for now http://www.necdisplay.com/Products/Product/?product=311c5952-12d1-44d6-84c6-e81120c4d482

ps2. i don’t know if you know this site, but when i want to calculate a distance and the brightness of a projector for using in an installation i always try this very complete calculator (you find all the projectors over the market) http://www.projectorcentral.com/projection-calculator-pro.cfm

i often use the optoma EW610ST but it does nave quite a bit of Y shift. Amazingly short lens on it and good brightness and price. Also RS232 control which is nice for installations.

oh yeah and I guessing that if you are mounting the projector on the ceiling but need to bring it down below the top of the screen and hence point the projector up a little because of the Yshift and offset, the projector my make some adjustments of the focus when you keystone this square again. This is an assumption, I can test later for you if you want. Not is office till much later though.

@screamer, those specific projectors won’t work cause they’re not 720p. The projector central site IS great. When I was on the phone with Optoma they actually suggested using the calculator on that site in addition to their own.

@xd_nitro, the US-version of your Optoma projector TW610ST might just fit the bill here. But FYI–this projector does not have lens shift. I found that some of the really hi-end Optomas do have this feature, such as…


The Optoma distance calculator gives a vertical offset range of 12.5-83in for the TX765W projector when setup for a 180in diagonal screen. Strangely enough, this range does not go into negative territory so this projector’s lens shift feature wouldn’t really help me anyway.

Also, since the EW610ST does not have lens shift, adjusting the Keystone will not effect the angle of the lens. Keystone is in fact a software-based operation which means that the actual projection rectangle does not change. Adding any amount of Keystone is essentially removing some pixels from the projected image in order to squeeze one edge of the rectangle.

That being said, I would be grateful if you could test your EW610ST. If you can put it on the edge of a table 7’8" from the wall (or as far as you can cause that’s gonna be a pretty big picture), angled down so that the bottom edge of the projection rectangle is one foot below the projector. Then adjust the keystone and focus. In this configuration, can you Keystone the image into a perfect rectangle, and can you focus the image so that none of the edges are out-of-focus? If that works well, angle the projector further so that the bottom edge of the rectangle is two feet below the projector and then retest.