david,
your point is well made: the panamorph does not introduce any keystone of it's own.
HOWEVER, the panny (752) is designed to provide same-height compression to 1.78 for projectors whose native 4x3 image is at the same height as the lens (ie: no built-in tilt.)
This means that if you currently have a level-mounted projector whose image falls below the height of the lens in ceiling-mount configuration (like my UP-1100 and countless others,) you will need to tilt the projector UP to maintain
image height, thus introducing keystone, JUST AS IF you tilted the projector up without the panny.
my projector was previously mounted perfectly level, with the top of the native 4x3 image ~12" lower than the projector's lens and zero (i mean ZERO) keystone distortion. i set this up in accordance with the LT-100 (clone) manual at
http://support.nectech.com/Vsd/dlp/lt100/lt100.pdf)
my throw is about 203" onto a 49x87" screen starting ~27" from ceiling. my lens is about 6" from the ceiling.
this doesn't seem like a strange configuration, afaik.
i had to tilt my projector up about 4 degrees to keep the
16x9 image in the same location (as using the projector's 16x9 mode.) this causes the top of the image to be more than 1" wider than the bottom. significant, imho.
i have 9' ceiling and cannot raise my projector any higher.
if i could lower my screen by 20" to eliminate the keystone forced by the panny (which i can't,) the bottom of my image would be ~12" off the floor - too low.
To me, it seems like the panny was designed for the high-end DILA's (with their zero tilt), not us average joe DLP owners...
fwiw: shawn claims to be mulling this issue over. he may be humoring me (and i wouldn't blame him, as i'm apparently the first to voice such concerns) but i believe this will prove to be serious problem for widespread panny acceptance among the non-DILA crowd...
ok, call me <whatever> but that's just too much keystone for me...
your mileage may vary. and as much as i'm bitching about the keystone issue, the overall effect of the panny is well worth what i paid for it a year ago, but i can't really recommend it at the retail/OEM price, unless you have a DILA or some other projector with ZERO built-in tilt.