Installation

Caustica is a complete Blender 5.2 LTS build, not an add-on. There is no installer and nothing is written to your system.

1. Unzip the archive anywhere you like.
2. Run blender.exe from that folder.
3. Enable your GPU under Edit > Preferences > System > Cycles Render Devices if you have not already.

It runs alongside your existing Blender. Because it is Blender 5.2, it uses the same user settings folder you already use — add-ons, preferences, themes and keymaps are simply there. Nothing to reinstall.

Windows may warn you on first start. SmartScreen shows "Windows protected your PC" for any program that is not yet signed with a paid code-signing certificate. Click More info, then Run anyway. A certificate is planned for an upcoming release.

Turning caustics on

Render Properties > Light Paths > Caustics > Photon Caustics Solver

That is the whole setup. Open an existing scene, tick the box, render. With the box off, the build behaves as official Blender.

The controls

• Photon Count — how many photons are traced. Higher means finer caustics without more grain. The default suits most scenes.
• Detail — buys sharpness at the cost of some grain. Works well with high sample counts and a denoiser; lower it if you render few samples.
• Intensity — an artistic multiplier. 1.0 is physically correct.
• Casters — All Materials, or Selected Materials Only to concentrate the photon budget on your hero objects.
• Cast Photon Caustics — the per-material switch used by Selected Materials Only, in Material Properties > Settings.
• Caustics on lights — each light has its own switch. Turning off fill lights sends the budget to the lights that matter.

Blender’s own Reflective and Refractive checkboxes also steer the solver. Light Linking is respected.

Render passes

Enable View Layer Properties > Passes > Light > Caustics to get the caustic contribution as its own AOV. Combined minus Caustics equals the render without them, so you can grade caustics separately.

If you use Light Groups, each group also gets its own Caustics pass, so you can rebalance lighting in comp without re-rendering.

Note: the per-group caustic passes are deliberately not denoised. Denoising is non-linear and would break the guarantee that the groups add up to the total. Render passes without a denoiser if you need them to sum exactly.

Suggested settings

• Look development in the viewport — defaults are fine. Caustics appear immediately and keep refining.
• Hero stills — high Photon Count, high Detail, high sample count, denoiser on.
• Fast previews — lower Detail. High Detail is grainy until samples accumulate.
• Jewellery and small-scale scenes — no adjustment needed. The gather radius is measured in pixels through the camera, so a ring comes out as sharp as a swimming pool does.
• Animation — no special settings. Every frame is deterministic and renders identically each time.

If you have more than one GPU

The solver currently runs on a single GPU. If you own several cards, tick just one of them under Edit > Preferences > System > Cycles Render Devices. Everything then runs at full speed — nothing else to change.

With several cards enabled at once it still renders correctly, and the caustics are the same. It is simply slower: the photon map is traced on one card and has to be handed to the others, and right now that costs more than the extra cards give back.

Spreading the photon map properly across all cards is in active development and will arrive as a free update.

Good to know

• Sharpness comes from the camera, not from the scene. The gather radius is measured in pixels, at the distance of the nearest caustic caster — the same approach V-Ray takes. Two things follow from that. Scene scale does not matter: model in millimetres or in metres, the caustics come out the same. And a small object no longer goes soft because something large happens to stand next to it.
• Because the radius is tied to the camera, framing and output resolution change it slightly. A 50 % preview is a touch softer than the 100 % final, and moving the camera closer sharpens the caustics. This is intended, and it is how other renderers behave.
• Caustics react to real geometry and displacement. Bump and normal maps are supported on the main surface, but not on the coat normal.
• On CPU the solver runs in its fast mode — the accurate material path is GPU only.
• Building at real-world scale is still worth doing — not for the caustics, which no longer care, but because light falloff, volumes and depth of field all assume it.

Updates

Your purchase includes lifetime updates — fixes, new features and rebuilds onto new Blender LTS releases as they arrive. Updates are published by replacing the product files, so the latest version is always the one you download from your Orders page.

What is coming next

Caustica went on sale three days ago, and the first update is already being worked on. Nothing here stops you from shipping renders today, but it is being fixed, and it will land as a free update like everything after it.

• Metallic BSDF — the standalone Metallic BSDF node is not yet picked up as a caustic caster. Metal caustics work today through Principled with Metallic turned up; the dedicated node is being added.
• Textured emission — when a light takes its colour from a texture inside an Emission node, the solver currently reads it as plain white. Constant emission colours already carry through correctly, including colours set on the light itself.
• Importing assets while Rendered view is running — pulling a model in from BlenderKit, or any import that swaps geometry on the GPU, can freeze the viewport while the solver is mid-flight. You will see:
  Illegal address in CUDA queue synchronize (photon_trace)
  Until the fix ships, switch the viewport to Solid before you import and back to Rendered afterwards. If it does catch you, restarting Blender clears it — nothing in your file is harmed.

Found something else? Write to [email protected]. Every report so far has gone straight onto this list, and this is exactly how it should work: one person builds it, you tell them what broke, it gets fixed.

That is what lifetime updates is meant to mean. You bought once. The work carries on.