Do you have any sample images that showcase the qualities you are talking about? I can probably search it up myself, but if there’s anything you would like to showcase. Thanks!
I don't have pictures online to show around. After using that lens for years now I think there are a number of factors contributing to this 3D effect:
* In the center of the image things behind the sujet are strongest out of focus.
* With the focus "plane" wandering off to the rear towards the corners, you can put up some "visual pillars" on the sides which are somewhat in focus, but shouldn't be from our own visual training. That seems to mentally push whatever is actually in focus in the center even further to the front. It also means if you just isolate the sujet without that most of the effect goes poof.
* On my A7s, through that field curvature, the corners are also somewhat smeared.
* The lens actually does have a lot of microcontrast in the center, i.e. is really sharp.
I mentioned this lens, because it is in certain ways superior than the Leica, but in overall has very similar visual qualities. It doesn't show in every wide open picture, it requires this "context" to work its magic, and some of the examples show that.
Another lens with this effect is the Voigtländer 21/1.8, but because it suffers in general in the sharpness department wide open it is less pronounced. I think on the above linked website there should be some examples for that, too. More perfect lenses look ... different. They certainly work better if you don't want these "visual pillars", so it is not like that field curvature is always the perfect thing to have, quite the contrary. However, it is a tool, or can be used as such, like so many other things in photography.
