Oh? I thought it was pretty clear and precise. The arbitrary zoom limit should be removed.
I'd love to know what further details you would like.

To reiterate after further testing:
When zooming in on a picture, it stops once one of the sides of the picture "fills" the screen. Ie, if the image is wider than my screen I can zoom in untill the top and bottom are aligned with my screen, but no further.
This prevents zooming in very far. And on a large (high resolution) image that prevents from zooming in on the details.

Edit:
Turns out that the zoom just happened to be the same on a couple of pictures (they had the same aspect ratio) so it looked like it stopped when the top and bottom hit the screen edge. But it was just a coincidence.

The point still stands. An arbitrary zoom limit prevents from zooming close enough on large images. It is unnecessary and a nuisance.