How to use Caustics in Cinema 4D?

Accompanying our V4 release of Corona Renderer for Cinema 4D, we have introduced our new super (super) fast caustics solver. Now, absolutely stunning caustic images can be rendered in basically just a few clicks. There is no need to adjust parameters and settings or "try your luck" with the old experimental engines as done before. The new caustics solver is easy to work with, supports reflective and refractive caustics, fast to render and it will take your images to the next level of photo-realism. Oh, did we mention it's fast!?

Swipe left or right to view the difference!


At the moment, the caustics solver supports the following features:


  • Reflective and Refractive caustics. (Glass, water, and highly reflective metals etc).

  • Dispersion in refractive materials (useful for diamonds, crystals, etc).

  • Motion blur (the caustics effect will motion-blur correctly).

  • Separate caustics multi-pass for post-processing.

  • Caustics work with both UHD Cache and Path Tracing.

  • Caustics from each light source will also be correctly adjusted by LightMix
  • Disable caustics from a light source or an environment light. Ie: HDRI or Corona Sky.


There are, however, also currently some limitations:


  • Caustics inside volumes are still calculated the old way and are not accelerated by the new solver.

  • Refractive caustics still require having caustics enabled in the material. Reflective caustics do not.

  • Only Corona Lights will produce caustics (standard Cinema 4D lights are not supported).

  • The new caustics use a Markov Chain Monte Carlo algorithm, which means each frame in an animation (or even rendering the same frame twice) will have a different pattern in the noise. To avoid flickering in animations, you will have to render a significant number of passes to ensure the solution has converged. 
  • Caustics may render slower/differently when using render regions (this will be fixed).

Setting up Caustics

As mentioned, working with caustics is extremely easy to set up. In the Corona render settings under the performance tab, ensure that you have 'Enabled' activated. By default, "Caustics only in caustics pass" is enabled, this means that you can render just the caustics to its own separate render pass and be composited later in a third-party software such as Photoshop for example. If you want the caustics to show up just in the beauty pass, you must uncheck "Caustics only in caustics pass".

If you are working with transparent materials such as glass or water you must also enable 'Caustic (slow)' in the materials refraction settings.

Highly reflective metals do not require the need to enable 'Caustics (slow)' as done for refractive materials. Instead, it is recommended to increase the Fresnel IOR to a value of 10 or greater.

Adding a caustics pass

A new caustics pass has been added to Corona's Multi-pass list. This allows you to create a separate render pass just for the caustics whilst keeping your beauty pass clean. This can be extremely handy if you want to have more control over the strength of the caustics when it comes to compositing. By default, "Caustics only in caustic pass" is enabled. If you only want caustics in your beauty pass you must uncheck this setting. Caustics generated from your environment can also be disabled in the render settings. This is useful to keep render times from any unwanted caustics. 

Unchecking this activates caustics in the beauty pass.

Caustics generated from your environment can also be disabled for any unwanted caustics. 


  • I can't see caustics!

    Make sure that your glass material has the "Caustics (slow)" option enabled under refraction properties and that you are using Corona lights and not standard Cinema 4D lights. 

  • I still can't see caustics in my render!

           Unless you are using the Multi-pass for Caustics, please ensure that "Caustics only in caustics pass" in unchecked.

  • My caustics are too dark!
    The caustics solver calculates physically accurate caustics and so the intensity of the light will directly affect the intensity of the caustics effect.

  • My caustics look strange with AI-based denoisers (Intel, Nvidia)

    Unfortunately, the AI based denoisers need to be trained to optimally denoise caustics and since the caustics solver in Corona is very new, there has not been enough time to train the denoisers. 

    Denoising quality of the AI-based denoisers will improve in the future as we work with both Intel and Nvidia on training their respective AI denoisers.

    The Corona high quality denoiser works with caustics perfectly fine.

    See: how to use denoising?

Are there some other tips and tricks on rendering caustics?

  • Do not enable caustics “just for the heck of it”. Rendering with caustics enabled is still slower than rendering without them and unless it’s absolutely necessary, keep caustics to the minimum.

  • Enable dispersion for highly refractive materials to add realism (e.g. diamonds). Beware, this will slow the rendering further, more than just having caustics enabled.

  • Avoid using atmospheric effects like fog with caustics. Even though it is supported, it has not yet been optimized and may cause slowdowns and excessive noise in the current implementation since the old method of calculating in-volume caustics is still being used.

  • Corona lights can also be controlled by the click of a switch. If you do not want a certain light to generate caustics, you can uncheck "Generate caustics" in the lights settings.


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