As much as the OP has gone about making their point in the wrong way, they do have a point. Caustics is slow in my experience (and I have a 3990x, paired with a i9 and some xeons).
Some of the response to the OP have been 'user error/rarely works out of the box/needs tweaking/use a different render engine then/that image is shit so caustics are the least of your worries' which as Marchik has pointed out, is the exact opposite of how it was sold to us as a 'new feature'. If we're told it works out of the box and is a 'one click solution' then why would we expect anything different?
Also questioning why you'd want caustics in certain scenes seems a bit odd to me, if your goal is to achieve ultimate realism, the scene in reality would have caustics and the tools you're using have a 'one click' caustic solution then why wouldn't you want caustics, no matter how small the effect on the scene? Sat at my desk just now and there are multiple examples of reflective/refractive caustics going on around me.
I saw Recent Spaces mentioned as a valid reference point for caustics working in production renders. Their work is great and the caustics look great, but following them on various social media channels it's evident that they've had to put a lot of R&D in to get it to that point, which suggest it really isn't as simple as made out. And to be fair, in terms of caustics, they are all still relatively simple scenes, outdoor, pool, single sunlight. I don't see any caustics on the dusk ones which would be the complex scenes in terms of lighting. They even say this themselves in your interview with them here -
https://corona-renderer.com/blog/recent-spaces-test-out-caustics-in-production-scenes/ "They’re now an essential part of making water look real, at least in daytime shots with strong direct light." And that statement pretty much backs up the only time it works as described in your marketing material - simple and fast-ish.
As already mentioned, it's great in simple scenarios, there's a reason why all tutorials/examples/demos for caustics are simple outdoor pools or a single glass with water in a studio environment, anything beyond this really does start to take forever. The demo scenes aren't your typical production jobs.
So far in this thread, I've seen 'send us your examples that you're having difficulty with' - I think the reason you've had no response to this is because there aren't any, people have cancelled renders before getting something worth showing.
I've tried to use caustics on a number of occassions and ended up giving up because what I was seeing wasn't worth the massive increase in rendertime. The difference in time between having/not having caustics is too great if you aren't equipped with a huge render farm and/or you're on a tight production schedule (which is a lot of the time). The example I tried was an open plan interior with some glassware/water on a dining table, a few highly reflective elements dotted around the scene and otherwise normal materials - the interior takes a couple of hours to render without caustics at 5k, turning on caustics more than doubles the render time. I don't think that's a particularly unusual scenario for a production job and it's one that in reality would definitely have and benefit from visible caustics adding to the realism. This project has some shots that I think would take a considerable amount of time to render -
https://www.archdaily.com/225678/shaw-house-patkau-architects and even then, they're still relatively simple scenes. Here's another not so typical example, that I wouldn't even attempt :)
https://www.archiproducts.com/en/news/raytrace-by-benjamin-hubert_70297So while these features are great in theory, they're usage is probably limited to the larger studios in a production environment for the time being. And although the OP had an interesting approach to making their point - it's not broke, but the point is still valid and when taking into account the 'marketing blurb' for caustics I think the responses are a bit 'off'.
A lot of frustration boils down to the marketing material and how things are sold - this
https://coronarenderer.freshdesk.com/support/solutions/articles/12000056738-how-to-render-caustics-with-the-new-caustics-solver- starts with "enabling effortless use of caustics in your scenes" and "Since the new caustics solver is a one-click solution, you do not have to worry about anything more than your materials in order to get plausible caustics effects." which are very enticing, so of course users will no doubt go and open a scene, enable caustics as described, only to then realise its actually pretty slow. Whereas had they scrolled to the very very bottom of the article they'd have found this tucked away "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."
TLDR the general vibe is that caustics are simple and relatively fast if you're rendering a pool, outside in direct sunlight. If you're not, it's probably not worth it unless you have plenty of time to kill.
