The main organ is located in front of the rose window at the western end of the cathedral. The main organ today comprises 128 stops and five manuals plus pedals. The modern organ is computerized, with full computer control of combinations and couplers and the like that allows each of the organists of the cathedral to define a personal configuration of the instrument for his preferences. The organist can also alter the way the keyboard responds to touch to suit his liking. The choir organ is used for routine stuff.
Several organists play the instruments in rotation.
The southwest corner of the bridge on the Left Bank side is the best vantage point, and it was the point I used for my main picture of the cathedral. The cathedral is very dark, as all cathedrals tend to be. For long exposures, brace yourself against something and hope for the best, and turn off the flash. Most cameras can do this.