I need to setup a ceiling mount camera to capture manuscripts

I have had to do exactly what you are attempting. Although the documents I was imaging were not quite as large. 80cm x 60cm or so. The problem you will run into is one of getting all the detail in one shot. I took several overlapping photos methodically from upper left moving to the right in as many rows as needed. Mine were old handwritten taped together pages of a family tree we were trying to preserve. Hopefully your documents are single layers and there won't be tape stains, offsets, mismatches, hard to read folds etc. I took the individual images and stitched them back together in PS. The results were acceptable. If you have a large number to try this on I would highly suggest building a platform, well lit with rails running above it that you can slide your camera along while keeping the same height. Reducing the amount of work you will need to do later. Fine writing in pencil is hard to capture from 1.5 meters away. As far as the focus and gravity, a little blue painters tape or a wide rubber band works. Check on youtube for large document scanning. Plenty of good examples. I would have built my own but I only had a few to capture. Good Luck!! Jeff

To do what you want even, high quality lighting is much more critical than what camera you use.

If you need to minimize geometric distortion and maintain high sharpness from edge to edge use the longest focal length prime Macro lens you can use in the space you have available.¹

_{¹ Since you didn't reveal how much space is between your mounting point and the document(s), telling us document size doesn't help much, as that is only half of the equation,}

Recommendations:

1. A lens with autofocus to deal with the potential for focus creep.
2. A camera that allows full control from a tethered computer to avoid fiddling with the controls of a camera in an awkward location and to allow aligning the subject with the camera rather than vice versa.
3. A camera that allows continuous external AC power to avoid changing batteries in a ceiling mounted camera.
4. Rigging a “goal post” from two C-stands, a piece of speed rail, a camera platform (rather than a tripod head) and various clamps, pins, and other ordinary rigging hardware designed for professional studio and cinema use.
5. Use of a mirror to align the camera parallel to the work surface. Place the mirror on the work surface below the camera. When the mirror reflects the center of the lens into the center of the picture the surfaces are parallel.
6. If the project is temporary, consider renting equipment rather than purchase.