I managed to figure out what the problem is and I see you have given me very good advice in your replies. I had some geometry far away from the model I was working on. It appeared when I imported a dwg file into SU and it was so far along the vertical axis I didn't know it was there. When i zoomed out and deleted it the shadows worked perfectly again, no clipping. Obviously focal length had nothing to do with my problems.
Thanks very much everyone

First one - shadows off, second one - shadows on.

I'm not a pro in SU, far from it actually, but i know the basics. So maybe i'm doing something wrong but before I started changing focal length everything was working fine. I could position the camera, turn on shadows and export. When I changed focal length and turned on the shadows the camera started clipping into the houses. If I turn off the shadows it goes back to a normal view, no clipping. So that's why I thought there might be a connection between focal length and shadows.

Hi.
I created a model in SketchUp, turned on the shadows and exported 2D images without any problems. Then I decided to change focal length and field of view and now, when i turn the shadows on again the view changes automatically. It jumps forward and it looks like my model is sectioned - i can see the inside of the houses. I then set focal length and field of view to default settings but it doesn't work. I can't shade the view that i want.
Does anyone know what to do?