--- title: "Caustics" canonical: "https://documentation.chaos.com/space/VC4D/116855220/Caustics" format: markdown --- This page offers information about the Caustics effect in V-Ray for Cinema 4D. ## **Overview** --- ## **Parameters** --- > Macro (anchor) ### Example: Search Distance --- For this example, the light used in the scene is [V-Ray Sun](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116850807). The Caustics method is set to **Progressive** and the **Search Distance** is set in **Pixels**. The V-Ray Sun has its Photon emission properties adjusted as so: **Caustics Subdivs** are at their default value of **1500**; the **Caustics Mult** is set to **2** and the **Photon Radius** is set to **30 cm**. > Macro (ui-text-box) > > Tips when working with progressive caustics: > > **Required**: > > - The **Affect Shadows** option should be off in refractive materials if they are to generate caustics. The option can be found in the [V-Ray Material's Refraction options](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855190), as well as in the [V-Ray Node Material options](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855972). > - The **Affect Channels** option should be set to **Affect all Channels** in refractive materials to ensure the **Caustics Render Element** contains also the ones fallen behind refraction. > Not doing so leaves photons fallen behind refractive surfaces inside the [Refraction RE](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855496), but not inside the [Caustics](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116853252) one. The **Affect Channels** option can be found in the [V-Ray Material's Reflection options](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855144), as well as for in the [V-Ray Node Material options](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855972). > - If present, the [VRaySun's ](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116850807)Photon Emission Radius should be set to a value large enough to encompass the relevant parts in the scene. > > **Optional** > > - It is **strongly recommended to set time limit** when rendering with Progressive Caustics, rather than relying on Noise Threshold value only. > - **Set a higher ****[Min Subdivs](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855825)**** value.** > A higher **Min Subdivs** value (16, 24, even higher.) means there is a longer phase of fixed sampling with no adaptation to the photon casting, so the screen coverage of samples remains more consistent, allowing for quicker filling of, for example, big flat areas or long thin lines. > The later phase of rendering, with adaptation, then just brings noise down to ensure the **Noise Threshold** is respected. > > **Managing Expectations**: > > - **The Progressive caustic solver is "fire and forget"**. > This means that it can be turned on in any scene, and *expected to trace photons on any specular or refractive surface*. > It doesn't, however, mean that doing so results in an image converged to perfection within a short time. > The approach, novel as it is, is still photon-map based, and judgement should be used to ensure quick, noise and frustration-free results. > > - **It renders with the beauty.** > The solver does indeed render happily alongside a beauty pass, storing caustics in the appropriate Render Element (see requirements tips above!), but that may not be the best solution as far as performance is concerned. > It's suggested to consider preparing a dedicated caustic rendering pass if the photon tracing is particularly extensive, and/or if sequences are to be rendered. > That way, it is possible to optimize the caustics calculation separately from the requirements of the beauty pass. > Macro (anchor) #### Progressive Caustics Advantages --- - they require nearly no setup; - each cast photon is more useful than those in traditional Photon Mapping; - the number of photons castable is only limited by time, not memory; - they can resolve tiny caustic details, compared to the scene size; - they can resolve caustic details also when a camera is very zoomed in on them; - statistics about the photon tracing can be found in the VFB2 stats panel; #### Progressive Caustics Limitations --- - they require the progressive image sampler; - this image sampler often requires **Min. subdivs** values much higher than 1; - it's non-deterministic, meaning that there could be somewhat unpredictable render times, and also tiny differences in the visual results when rendering the same frame twice; - currently doesn't work with distributed rendering; - Depending on the scene, the performance might not scale linearly with the number of threads/cores, resulting in inefficient CPU utilization. ### Photon Map method --- > Macro (rw-ui-expands-macro) > > > Macro (rw-expand) > > **Multiplier** – Controls the strength of the caustics. It is global and applies to all light sources that generate caustics. If you want different multipliers for the different light sources, use local light settings.  > > **Search Distance Units** – Specifies the units of the caustics photon lookup radius. You can choose between **World** or **Pixels**. When V-Ray needs to render the caustics effect at a given surface point, it searches for a number of photons on that surface in the area surrounding the shaded point (search area). The search area is a circle with a center at the original photon and its radius is equal to the **Search Distance** value. Smaller values produce sharper, but more noisy caustics; larger values produce smoother, but blurrier caustics. *For more information, see the **[Search Distance example](https://docs-chaos.atlassian.net/wiki/spaces/VC4D/pages/116855220/Caustics#Caustics-searchDist)**.* > > **Search Distance World/Pixels** – Specifies the photon lookup radius in pixels or world units. > > **Max Photons** – Maximum number of photons within the search area circle that are considered when rendering the caustics effect on a surface. Smaller values cause less photons to be used and the caustics are sharper, but noisier. Larger values produce smoother but blurrier caustics. Assigning a value of **0** means that V-Ray is not limited and uses all the photons that it can find inside the search area. > > **Max Density** – This parameter allows you to limit the resolution (and thus the memory) of the caustics photon map. Whenever V-Ray needs to store a new photon in the caustics photon map, it first looks if there are any other photons within a distance specified by Max density. If there is already a suitable photon in the map, V-Ray just adds the energy of the new photon to the one in the map. Otherwise, V-Ray stores the new photon in the photon map. Using this options allows you to shoot many photons (and thus get smoother results) while keeping the size of the caustics photon map manageable.  > > **Caustics Photon Map File** – Specifies the file used to load the caustics photon map when the **Mode **is set to **From File**. Click the Browse button to the right to specify the file name. > > **Auto Save** – When enabled, V-Ray automatically saves the caustics photon map to the file specified in the **Auto Save File** field when rendering is complete. > > **Auto Save File** – Specifies the file to which the caustics photon map is saved when **Auto Save** is enabled. Click the Browse button to the right to specify the file name.