At the moment, the new image lightbox seems to zoom to an arbitrary 300% when clicking the image, which is somewhat surprising compared to other image views, such as browsers when they display an image file.
I think it would be more natural to match the behaviour of other image viewers:
- For small images that fit in the viewport, display them at 100% by default, and clicking the image is disabled
- For large images that would overflow the viewport, shrink to fit by default, and enable clicking the image to toggle between 100% and shrink to fit