I had some strange rendering problemsw hen rendering a scene with an
object like this :
#declare MyObject1 = difference {
  cylinder { <0.0,-0.07, 0.0>, <0.0, 0.07, 0.0>, 85.935 }
  cylinder { <0.0,-1.00, 0.0>, <0.0, 1.00, 0.0>, 85.815 }
}

It looks like someone has cut some part of the 'sides' of the cylinder.
The endcaps are O.K., but it looks like two disks instead of a solid
ring.

This object is used within a pretty complex CSG, but the same problem
exists when rendering the object on its own.

When the ratio of radius to hight is > +/- 500, the problem disapears.
I had to solve this by using a higher cylinder and cutting the ring with
a plane :

#declare MyObject2 = difference {
  cylinder { <0.00,-0.07, 0.00>, <0.00, 5.00, 0.00>, 85.935 }
  cylinder { <0.00,-1.00, 0.00>, <0.00, 6.00, 0.00>, 85.815 }
  plane { y, -0.07 }
}

It should be seen with a little scene like this :

camera {
  location <-0.5, 0.5, 0.5>
  look_at <0.0, 0.0, 0.0>
}

light_source {
  <-5.0, 5.0, 5.0>
  color rgb <1.0, 1.0, 1.0>
}

object { MyObject1      //PROBLEMS !!!!!
// object { MyObject2     //PROLBLEM SOLVED !!!!!
  pigment { color rgb <1.0, 1.0, 0.5> }
  transform -85.875*y
}

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