Reply To: Specular vs. roughness?
@techworker1 great question. Conceptually, yes, increasing roughness to 1.0 has a similar effect to a specular value (“IOR Level” in 4.0+) of zero. It’s hard to tell the visual difference in the renders below, but the one with specular at 0.5 and roughness at 1 (A) is a touch lighter from the reflection. Overall I qualify the difference as barely noticeable.
(B) is the same except for specular (IOR level) at 0.0 for all materials. Notice how A rendered slightly longer at 9.42 seconds compared to 9.29 in B. The thing to consider is that reflections take longer to calculate. It’s quite a small difference in this simple example but if you have a scene with hundreds of objects with 1.0 roughness reflections, it could be quite significantly longer render times or noticeably more noise in the results.
My practice is to leverage a 0.0 specular value for objects that appear “entirely diffuse” or “matte” rather than a roughness of 1.0. In fact I rarely use roughness above 6.0 because reflections get very subtle beyond that point and it’s not worth the extra render calculation. BUT I wouldn’t deny a claim that higher roughness is technically more accurate than specular at 0.
I hope that helps clarify!