Hi,
“zooming” can have different meaning depending on the context… In a orthographic camera context, it means reducing the frustum, and in perspective it could mean moving the camera forth OR decreasing the FOV.
So what you really want to do I guess is to tweak these parameters depending on the camera your are using, in order to make an object take the same space on screen.
There is a thread where you can find how to do this, and if you search the forum you can find more.