I have an R100 APS-C Crop Sensor camera and have been looking at options for a lens with macro capability. My interests are mostly landscapes and wildlife, and the macro aspect interests me because it provides a way to get better photos of some of the smaller things in our outdoor world.
When I look at other RF series lenses, NOT RF-S lenses, you apply a crop factor of 1.6 to get the equivalent focal length. For example, I have an RF-28mm prime lens, which gives me pretty much a "nifty 50"...