distortion of the material when rendering

[Assyl]

Hey! Can you tell me why it appears and how to get rid of it?

[burnin]

If you mean distortion you get on the roof tiling, it's called Moire Pattern/Effect.

V-Ray Example: Anti-aliasing Filters and Moire Effects

You can somewhat get rid of it by couple of different techniques - either using "right" AA Filter or "Super-sampling" (render bigger image and after down-scaling it).

[Assyl]

This is a profiled sheet. Why does the corona material fit like this? I mean these incomprehensible circles.

[Beanzvision]

This will even happen with standard C4D materials. Did you try the recommendations above? What size is your render, have you tried increasing it also?

[Assyl]

The geometry is correct. Higher resolution doesn't help. The number of passes is the same. the solution should be simple.

[BigAl3D]

You are definitely running into the Moiré effect. This was always a concern with broadcast video since the resolution was so low (720x486). The angle of your lines plays a big part in it as well. The only solution is to change the angle, enlarge the pattern or increase the resolution. The image that Beanzvision posted is spot-on. The scaled-down image doesn't have the resolution to resolve the detail and it conflicts with the screen's pixels. This is why top professionals on TV never wear fine patterns on camera. Their clothes will dance with this effect. In this example, notice the farther away the camera gets (lower effective resolution), the worse the shimmering gets? Same problem you have here.