The guide
Small enough to work properly
The island is about seven hundred metres long and one street wide. Everything on it — the quays, the bridges, the shopfronts of the rue Saint-Louis-en-l'Île, the view of the cathedral — is within a few minutes' walk of everything else.
That compactness is the practical argument for it. A session here spends its time photographing rather than walking, which is the opposite of what happens when somebody plans a session across three arrondissements.
Two levels
The upper quays give you the classic frame: plane trees, stone parapets, traffic in the background, the mass of the cathedral to the west.
The lower quays, reached by steps, are a different place entirely. At water level the city disappears, the river becomes the whole background, and the noise drops away. It is where we take most of the frames that people actually keep.
Winter floods close the lower level regularly and without much notice. It is worth checking rather than discovering.
The crowd, and the twenty minutes
This island is on the route between Notre-Dame and the Marais, so by mid-morning it carries a continuous stream of people, and in summer it is dense enough to make a couple session self-conscious.
Before nine, it belongs to residents walking dogs. The transition is abrupt — about twenty minutes — which means an early session gets the whole island and a session an hour later gets a queue for ice cream.
What it suits
A short, dense Paris session where the point is to look unmistakably like Paris. Couples, especially at the lower level. And proposals, because the eastern tip gives a photographer a place to stand at a distance without looking like anything other than a tourist.
It is ten minutes' walk from the Marais and from the canal, so it combines easily. Rates are on the rate card.