In full screen mode there is a large empty space around the whole image. On a mobile this is ridiculous waste of screen, and is nothing to do with preserving aspect ratio. Many others are asking how to do this with fancybox.
Please see attached image - the top photo shows what happens immediately after clicking the full-screen icon. Total waste of space around the image. The lower photo shows what should happen. Aspect ratio is the same in both. The whole photo is visible in both.
Are you able to help with this?