[itsallgoode9]

Unless I misunderstand, both of these effects are a way to fake microgrooves and microbumps on a surface.

If I am doing a very high res render closeup of a surface, such as brushed metal (for an example of the anisotropy)...would it be more correct to use a really high res bump map to actually create the anisotropy effect through actual grooves in the metal? While leaving the anistropy at 0?

The same question goes for the roughness.... for example, a really high res close up image of a a piece of semi glossy plastic. The best random example that comes to mind is the plastic of a TV's remote control. Would it be more accurate to create this semigloss plastics look through a very fine bump map while leaving the roughness setting at 0?

I'm thinking that in an image where those specifica surfaces aren't close to the camera, that it would be best in both situations to use the roughness and anisotropy, but if it's a super close up it would be better to semi-physically create those effect through using bump maps.

I'm not sure the correct answer so i'm curious of you guys' thoughts.

[Hervé]

well mostly correct.. but you can also mix both techniques.. it all depend how far you are.. what do you want to do.. voila..

[Bubbaloo]

In some experiments I did a while back with brushed metal close-ups, I settled on using just a super high res 16 bit roughness map. Displacement, bump, and anisotropy all looked unrealistic at super close distance. Besides, the micro grooves in this type of metal can't be seen as bumpy by the human eye, only under a microscope. Although you may be able to get some anisotropy in with it to enhance the effect.