Please send us more details about the issues you are reporting. Things such as viewport screenshots and example renders would be great, and scenes where those issues can be easily reproduced would be perfect. Please see this guide for basic information how to report issues to us: https://coronarenderer.freshdesk.com/support/solutions/articles/5000524006
If you are not willing to share your images or scenes publicly, you can contact us at support@corona-renderer.com or using this form: https://coronarenderer.freshdesk.com/support/tickets/new
No changes planned to the caustics for Corona 6 (if there were, they would be on the roadmap). As Marcin mentioned, seeing the scene and results you are getting would help us know if this is just a scene setup problem, a bug, or something that is working but could be made better. Right now though, we are in the dark about any of that.
Please send us more details about the issues you are reporting. Things such as viewport screenshots and example renders would be great, and scenes where those issues can be easily reproduced would be perfect. Please see this guide for basic information how to report issues to us: https://coronarenderer.freshdesk.com/support/solutions/articles/5000524006
If you are not willing to share your images or scenes publicly, you can contact us at support@corona-renderer.com or using this form: https://coronarenderer.freshdesk.com/support/tickets/new
Third time’s the charm?
Please send us more details about the issues you are reporting. Things such as viewport screenshots and example renders would be great, and scenes where those issues can be easily reproduced would be perfect. Please see this guide for basic information how to report issues to us: https://coronarenderer.freshdesk.com/support/solutions/articles/5000524006
If you are not willing to share your images or scenes publicly, you can contact us at support@corona-renderer.com or using this form: https://coronarenderer.freshdesk.com/support/tickets/new
@madcat117 - do you know any renderer that can do what you want? Otherwise it sounds like: Bummer, why won’t you make my Ferrari drive 100km pr liter. I need it!
First of all, why do you need caustics at all in this specific scene, and in this specific place?
Maybe you can just get rid of them in the unwanted areas using the rayswitch material or some other workarounds?
Check this out: https://coronarenderer.freshdesk.com/support/solutions/articles/12000066318
Just a note, it all depends on your scene, so saying you “have to use” is not true. For example I am rendering a scene (pretty simple, just gemstones on a plane, but lots of gemstones) and it only takes 40 or so passes - while it is a much simpler scene, it illustrates that what you “have to use” depends entirely on what you are rendering).
“Your current caustics solver does not work for production scenes” again depends on your scene and what you are looking for. Recent Spaces use it in production scenes a lot these days https://www.recentspaces.com/lathampools and those are not simple scenes 
I use caustics only for stills. I also have huge amount of fireflies from pool caustics but I use caustics channel and edit it in ps. But it would be nice to know how to use caustics in anims or how to get clean caustics as in link provided by TOMG.
Throwing caustics into a random interior scene will most probably never work. There is always some manual optimization needed. I am pretty sure it’s the same with all other render engines which feature caustics. And it isn’t like that only with caustics. You often have to be careful with reflections, lights, etc. You can’t just enable all the cool-sounding stuff and call it a day.
@madcat117 - as I already asked once: please give an example of one of those “other renderer” that does caustic faster and better.
Otherwise I’ll consider you a troll.
I’m starting to notice that people want corona to compensate their lack of abilities/talent/effort
Not sure I’ve seen that elsewhere.
Corona is just a tool, I bet if they could make caustics an order of magnitude better, they would have already. If you don’t like something as fundamental and you believe it’s a crucial ingredient to realistic renders, the smartest thing to do would be to use other render that does offer what you want.
Please post your renders that are so complex and absolutely need caustics, that bathroom picture is bad for many reasons other than caustics.
Btw. You should buy the 3990x because it will make everything in your live better, not just caustics.
You’ve had your chance.
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 - What are caustics and how to render them the right way “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 - Shaw House / Patkau Architects | ArchDaily and even then, they’re still relatively simple scenes. Here’s another not so typical example, that I wouldn’t even attempt Raytrace by Benjamin Hubert
So 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.
@dj_buckley
Let me hug you, bro exactly my thoughts, except that I dont have 3990x and I am the one who tries to kill all my time, achieving maximum realism
Here’s another way of looking at it. Rather than asking for scenes that demonstrate it doesn’t work as expected. Let’s ask for scenes where people have successfully used caustics on a live arch viz client commissioned production job (other than an outdoor sunlit pool or closeup of a glass/water). I don’t think you’ll find many - if any at all but I’ll happily be proven wrong.
We used caustics on an animation of a residence with a pool. It worked well after some experimentation, but we rendered out caustics as a seperate pass and masked it on in after effects. There were too many fireflies on the walls of the adjacent buildings, etc. This was on a 3990x machine and even rendering quite a few passes didn’t solve it.
The two big things I see as improving caustics would be:
1 - Include\Exclude for either objects or materials for receiving caustics. That way if you have a wall that doesn’t even ‘need’ caustics but is getting dancing fireflies you could just exclude it, much like how you can exclude certain lights from generating it.
2 - Playing better with forest pro elements. I find my caustics REALLY speed up when I start hiding grass and trees. Probably not really forest pro specific, maybe something to do with complex geometry or opacity maps.
The only other glitch I’ve run into is when I had kind of a low quality bump map on my water…but that was my fault and I fixed it
All this said, I have had much better luck with Corona caustics than I have had with VRay’s over the years. So all this is just a matter of degrees, in my opinion.
Thanks everyone for your feedback. Especially dj_buckley for the exhaustive post. We will definitely take this forum thread into account when deciding about what to improve in our caustics solver and how to prioritize it.
I will just leave this short reply here, and will return later with some further info (or alternatively someone else from the team). It seems that there is a difference between the developer and user point of view here, and also our marketing/support materials do need some clarification.
(Internal ID=529569515)
this is exactly what we wanted to hear from you guys, thanks to Maru and the entire development team, corona is an excellent render engine, otherwise we would not write here) I hope you will surpass yourself again and we will get the best tool on the market to achieve the maximum photorealism, as always.
PS
if possible, I would like to learn from you about the possibility of introducing a calculation of caustics in volumes, how realistic is it in the foreseeable future, or is it better to forget about it)