Creating realistic glass in Cycles for Blender 2.73a

I’m trying to create a glass material that is physically accurate for my architectural renders.
I’ve seen that the most common method for creating glass involves the light path node.

But none of these create actual caustics on the surface behind the object. For example, the scene attached shows a sphere made of glass using the light path node.

Light makes it through, but isn’t focused behind the sphere like one would expect in the real world. This use to be possible using the ‘Filter Glossy’ setting on the render panel, that that doesn’t seem to have any effect anymore since Blender 2.72.

Does anyone have a node setup for physically accurate glass? Or is this an issue in the software?


For the most accurate glass, just use the glass bsdf node, that’s what it’s for. The other setups you see are all hacks to render faster. You can add the volume absorption shader to the volume output if you want some color filtering.

And btw, if you’re after realistic caustic effects within a reasonable render time, Cycles is not your friend… You might want to check up on other render engines.

Thank you. I’ll give that a test. I’m willing to spend the extra render time if it looks more realistic. I’ve yet to find a program that does caustics really well without taking a long time. I’ve seen others that can fake it and render faster but it doesn’t look as good.

Plus with GPU support it’s not as bad as it once was! :smiley:

Cycles and “real” caustics is not about spending some extra time. It’s about waiting forever and still getting nowhere.
Cycles is in no way equipped to render refractive effects like that efficiently. Just for comparison:

This is a 5 minutes Thea Render:

And this is a 2.5 hours Cycles render (around 50.000 samples):

Give Thea another five minutes and the image might be perfect. Give Cycles another 2.5 hours and the result will still look unsatisfactory. There is no way around faking them if you want to have at least a vague impression of caustics in Cycles.

I got a way to push the caustic effect in cycles but not realist!

best bet would be with other renderer like Yafaray or Luxrender

happy cl

Ah, I see. Yes it does seem that my biggest hurdle might just be that Cycles doesn’t really do caustics. I also found that my first issue was that I was using a lamp instead of a mesh light. Cycles does not calculate caustics for the default Glass BSDF shader unless you are using a mesh light.

But it looks like I’ll need to use another rendering engine if I really want realistic results.

Thanks for all the help.

That’s not true*. In my Cycles render above the light source is a simple point light. Just make sure that “Multiple Importance” is checked for the light and that it has a significant radius: The smaller the light source, the harder for Cycles to “find” it and the slower the convergence.

That’s also why Cycles’ caustics look less defined than Thea’s in my renders: Ideally you would use a very small point light to get sharp caustics. But if you do that in Cycles, the already slow caustics calculation slows down to an unbearable crawl.

*At least not for Blender 2.75a.
Can’t really remember how things were with 2.73a… BTW, is there a reason why you stick with that version?

Not completely true. I find the glass node unusable due lack of independent controls for reflections and refractions, which is why I prefer a custom glass material for volumetric glass. For sheet glass (like windows, where refraction doesn’t matter), I’ll happily use a custom sheet glass material giving me the same kinds of control possibilities. Glass in TV or eyeglasses can have anti reflective coatings, whereas (old) building glass can have reflective coatings and typically never a single layer of glass but two or three. Modeling this for “realism” is of course just dumb. Speed is essential. “Hacks” give me speed, and I get much happier.

Sure, some “hacks” provide fake caustics and shadowing effects. Node setups looks complex, but rendering speed compared to “real caustics” (which have been demonstrated is not for Cycles at all in the first place) are pretty much free.

That said, why on earth would OP want to use caustics for architectural renderings?

I’m working on an interior scene with knick-knacks that will be visible enough for me to need to do some sort of caustics. I find that most hacks don’t appear to be very accurate. My main goal is to produce as photo-real an image as I can. Thank you all for the clarifications This has been helpful.