render black circle ?

in latest buil I got this render
and did not change anything I my set up
what is causing the black circle in background in render output?

thanks for any feedback
happy bl


Looks like it’s Fresnel applied to backface (inverted normal): try flipping normals of the plane, or giving it 3 dimensions (ie put a solidify modifier)

already check that and it is ok
normals are out and it is a thick solid slab not a plane


I got a simple diff gloss mix shader node
very simple

and yup I disconnected the glossy node and it is gone

why the heck in this case is It doing that

not normal I think but why is it a bug ?

looks like a strong Fresnel effect at radial distance from camera

if I move camera back then circle is moving backward too
but still there

happy bl

can you post the blend?

here is file

tried different locations for lamps ect.
but does not seems to change much

happy bl


reflect-law.blend (103 KB)

indeed a normals problem. you have your plane set to smooth shading. you can:
set it to flat in edit or object mode
put an edge split modifier
use auto smooth (mesh-data panel)
set each edge to sharp in edit mode

i suggest the first option

what does it do or how it does that ?

I mean I did another file with same set up and it does not do that at all


will experiment with that smooth thing

happy bl

I see the smooth and flat effect

looks like smooth is making the face like a sphere with some Fresnel

is there an indication on screen that ob is smooth of flat may be?

happy bl

yes you can see it at first glance in viewport: smooth doesn’t show hard edges. Just try to toggle smooth/flat and you’ll see what i mean