Lightbox images are too big

Good evening!
Your theme is absolutely wonderful but I’ve encountered a little trouble. Namely, I have very large photos which I don’t want to minimize (I mean: I don’t want to reduce the resolution of them). And after opening a lightbox with one of the big photo on a post, the picture is completely out of the display (it’s not responsive, it’s seen only a zoomed in small part of the whole photo). Is there any way to fix that kind of problem? Is it possible to display pictures responsively?
I’m looking forward to your reply.
Best regards.