Hello!You have no reason to find good lessons about caustics. Not because I did not look well, or someone could not write an explanatory lesson. Everything is much more banal. You did not find them because the algorithm itself for calculating the caustic is clumsy. And this does not apply to the viraiya or mentala. Simply this is a very complex light phenomenon (phenomenon), which is not fully understood and all the engines imitate it rather not physically, but visually. Just make a fake.At the moment, the most common algorithm for calculating caustics (light trajectories / lines) is photonic mapping, which simulates the behavior of light rays, literally firing photons (portions of light energy) into the space of the scene. Then, he tracks their behavior and, after a few rebuffs / bounces, from the surfaces of the scene, writes light information into a so-called photon map. Nominally, it is used as a GI algorithm.That is, thousands of rays shoot from the light source into the scene. Kony horses will be distributed, how they will be reflected, what will be the result - even the developers of the renderer do not know. It's simple, unpredictable. Thus, the whole scene is filled with chaotic light information. Moreover, the relative accuracy of the result obtained, directly depends on the number of these photons (caustic). The more they are emitted by the light source, the more detailed will be the photon map (caustic map). Otherwise, from the lack of photons, there will be dark corners in the scene (since not just one photon has simply not fallen into them), incorrect illumination of light / color artifacts (color music, as in your rendering😁), etc. By the way, the photon map even looks like a bunch of multicolored spots that have stained the scene.In order to get rid of these problems as much as possible, it is necessary to increase the number of photons fired by a light source. This will inevitably lead to an increase in the light information recorded on photons. How much RAM do you need to get a beautiful detailed photon map? Two gigabytes? Three? 10 gigabytes? In this every now and then, the more the better. So, on a computer with 4 or 6 gigs oz, a normal photon map can not be dreamed of.To simulate the caustic effect, in the vira, a modified version of the photon mapping is used, the so-called Caustics algorithm, which has all the "buns" of the main photonning. The same requirements for the number of photons (RAM), the same artifacts. This is the same Photon mapping, but, taking into account only photons that have passed through refractive materials. That is, through objects with transparent and translucent mats. For example, the materials made by VRayMtl base with the color Reflection, other than black.What are the conditions for the appearance of caustics in the scene?First, the light source emitting photons, of course, the more directional it will be, the more pronounced will be the photons.Secondly, the presence in the scene of materials with refraction.To mats themselves, there are no special requirements. The mat should be transparent / translucent.Third, of course, it is necessary to activate the Caustics algorithm itself in the scroll of the same name, the folds of Indirect Illumination.He has only four parameters. Multiplier, Search distance, Max photons and Max density.The first is just the power of compositing / mixing the render of the VrayCaustics element in the main render. The larger the multiplier, the brighter the caustic effect.The second is a zone for collecting information about caustics on the surface of objects in the scene.As I said, the photon map, yes IM, it's just a map of color spots on the surface of the scene objects that are calculated, depending on how much, what color and intensity of the rays hit the zone of this spot. In our case, rays are caustic. For example, 10 beams fell into the information gathering zone. Renderer takes their colors and intensities, and then mixes them into a common average color. Thus, the entire zone becomes one blurry light spot.Hence it is not difficult to guess that the smaller the collection zone, the smaller the spot size and the more detailed the caustic map will be, but also the more noisy (spotted😁). Of course, for smaller collection distances, more photons are needed.The third one is just a limiting value that works like a Noise threshold in the DMC Sampler, which simply stops the calculation of the effect, after a certain number of photons in the data collection zone.The last parameter is designed to optimize information about photons in the RAM. It does not affect the rendering itself, but it is responsible for monitoring duplicate information about the fonts.That's all.Gus_ann, as I understand it, you need some advice on how to set up caustics.They are, as in the case of object-oriented 3d visualization, but you will not like them much. Because the only one let's set up beautiful caustics in the scene, it's a race. At random, selecting and experimenting with the right number of photons, the position of the light sources, the optimal size of the distance of collection, etc.Of course, if you experiment for a long time, you can already, at the level of intuition, foresee how, in this or that scene
That itself is a scene in a format 3ds Max 2008 included caustics .
As to the form of glare, etc., is simply to pick up, changing the position of the light source, a ring shape, the parameters most carat caustics.
V-Ray Caustics by Ricardo Eloy