If you are working in small spaces or the projector has to be closer to the screen, you will need an Ultra Short throw lens projector. There are two types, some which have build in lenses and some, which use attached mirror lenses. These lenses may shoot over the back of the projector, as shown in the left image.
Because of this lens arrangement, the image is pushed lower (offset). Now if you have a high enough ceiling, this may not matter, since the centre of your image will still be optimal to your viewers eye level as the top of the image moves up with the position of the projector. But if you have a low ceiling your viewers may have to look down.
Of course you could correct some of this with image shift up or by tilting the projector. But tilting is fraught with danger, since the short throw lenses distort strongly, at even slight tilts and the keystone adjustment may not be able to correct this.
If you have a non-offset projector, this issue does not apply. We are using here the Fujifilm Z-series projector, which has a unique 360 degree rotational lens and an extreme image shift. The lens can actually be turned to work from the front edge or the rear of the projector. The lens will project the top of the image to the same level where the lens is. This puts the picture at a higher position, easier to view. If needed the high image shift actually lets you move the image down without having to tilt the projector. So no distortion.
This arrangement works both with floor and ceiling mounted projection. It not only solves you set-up issues, but improves the overall image quality, since the projection beam is not distorted in the first place.
Projector: Fujifilm Z5000 and Z8000.
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