Photographer's Resolution panel allows you to use different resolution per camera.
Format: Set a ratio from common photography ratios, or set your own custom ratio or resolution.
Long Edge: When setting a ratio, you can then adjust your render resolution with a single resolution size. The Short Edge will be calculated from this value.
Percentage: Set a percentage ratio to quickly render smaller versions.
Orientation: Switch between Landscape (Horizontal) and Portrait (Vertical) framing.
Fit inside Sensor is a smarter Automatic Sensor Fit that makes sure the image cannot be rendered outside of the actual Sensor Size. This ensures physically-correct Field of View that matches real-life cameras. It is recommended to enable it especially when incorporating 3D assets into photographs.
However note that when changing resolution values, your framing might visually "jump" in the viewport. This is expected and simply requires to reframe the viewport without Lock Camera to View.
Resize Canvas (Experimental)
Similar to Photoshop, the Resize Canvas allows you to expand or reduce your rendered image framing using Anchors.
Important: this feature comes with several limitations:
Sensor Fit cannot be automatic, a warning button will pop and allow you to fix the Sensor Fit before using Resize Canvas
As Resize Canvas makes use of the Camera Shift properties, using both Resize Canvas and Lens Shift can lead to unexpected results and changes of perspective.
Resizing Canvas can be stacked only using the same Anchor. In order to change the Anchor, you will have to revert the previous Resizing.