We are talkin about this. 

Plate surface are easy. How do you achieve this here ? 

More or less the same?

Sorry, but it's not the topic. non blame here but you are not in the right subject. 

They are talking about reflection plane to have a mirror surface. So, in the cases you send here, there no mirroring surfaces on both of your semi sphere.

The goal of the renders I posted, is to show you that have a spheric shape with mirroring surfazces is impossible with reflection plane, because this tool is flat, so no possibilities to apply on a circle surfaces to acheive this. 



Where is the renders I shared, you see the drum miroring on the sphere, on the bench etc.....

So I was not referring to any spheres at all, I was indicating  on circled flat shaped stages / round corners on stages, so the overhang of the plane creates blacks on the lower layers of stage platforms please see image indicating below in red.

How, my mistake sorry

yup it's annoying !