View Full Version : Difference between "Ray Recursion Limit" and "Reflection Recursion Limit"

03-05-2018, 11:52 PM

Could someone explain the difference between the "Ray Recursion Limit" and "Reflection Recursion Limit" in the Render Properties panel.
I try to see the difference in some examples, but it is not evident on how they behave in a different way. The doc (link below) is not clear for me, it says that in both case reflections are concerned :


So, if someone has a better explanation, thanks.

03-06-2018, 06:02 AM
reflection recursion is for reflections. mirror like reflective surfaces, metals, clear coat.

ray recursion is for light. so would affect your lighting in the scene. how many times the light ray bounces.

diffuse bounces being for gi. how many times the global illumination bounces around while sampling the scene.

as i understand it.

what i would do is grab a cornell box or similar test scene, chuck a light in there some place, drop the lot to 1 or 0 then start adding to each one at a time, to see the effects.

03-06-2018, 08:30 AM
Thank you for taking the time to answer.
I wil investigate in the direction you propose.

03-06-2018, 08:35 AM
yeah i hope that’s useful. someone else might have a better explanation :)

03-09-2018, 08:13 PM
If you position a semi-transparent mirror in front of a solid mirror, you get an infinitely repeating series of reflections. It works with strings of lights, and with small set pieces. Here's an example from a Halloween enthusiast for a bottomless pit illusion.


Unfortunately, with infinite reflection bounces, the rendering engine will bog down and stall, so having a limit makes sense. You can set it higher when you have lots of reflective objects in the scene and you really do need to see a reflection of a reflection of a reflection.

03-09-2018, 11:20 PM
Thank you for your answer KurtF.
I understand what you say and it is clearly explained in the lightwave docs, but the difference between Ray Recursion limit and Reflection Recursion Limit is difficult to understand in practice. I try several to configure a scene where I can clearly see their difference but with no succes at this day.

03-10-2018, 07:36 AM
Ray Recursion Limit is simply global recursion limit. It affects numbers of reflection, refraction, transparency and even number of GI bounces. If you set reflection recursion to 6 and Ray Recursion Limit only 3, you will get only 3 reflection bounces. Same for refraction, transparency and GI bounces.