A simple studio shot takes ages to render

[Alex_M]

I've got a studio shot with simple food containers. For the life of me I can't find a way to render it! It's taking ages on my 4930k. The scene is very simple - HDRI light + 2 directional disc lights and some refractive food containers on white backdrop. Render settings is mostly default with minor tweaks that shouldn't hinder performance, to the contrary. So why is it so slow to render? I don't think I've ever encountered a scene that simple that is so slow to render. Should a scene like this be that slow?

Screenshot of the scene and the container material:



Oh, and another finding that's been bugging me for a while. Ever since Vray 3 or later, I've noticed that light cache calculation is very slow with refractive objects. Much much slower than with opaque objects. Refractive objects just kills light cache. Even on low subdivs (100-200) it feels like it's calculating 1000-2000 subdivs. I don't remember this being the case 3-4 versions back. Is it just me and have others noticed that to?

Anyways, any help with rendering this scene is greatly appreciated.

PS: I did a test with Corona. It takes just 2 minutes to render what Vray needs whopping 8-10 minutes. I also see Corona's light cache (called HD cache) takes approximately 3-4 times less time to calculate. So I'm getting 4-5 times less speed with Vray. This certainly can't be normal, can it?!? See below:



I also tried rendering this scene with the GPU from my signature by putting RT CUDA in production render mode. My PC completely locked 10-20 sec. in rendering and I had to restart my PC as I couldn't even bring up Task Manager to kill Max.

[glorybound]

What's slow? What was the resolution and render time? How about your V-Ray settings?

[Alex_M]

As already mentioned in my initial post and as seen from the screenshots, render settings are practically at default and the resolution is 800 x 600. I just don't want to think about how much time it would take me to render that scene at 2400 x 1800 with Vray. Maybe a day or two. As soon as I'm not using refractive materials, it renders blazing fast - within seconds I have a clean image. Then I apply the plastic material to the containers and BOOM! It now suddenly takes 10 minutes per pass. I'm worried how and if I'll be able to deliver those renders. I'm now actually trying to figure out how to fake that plastic material to avoid the ridiculous render times as I have to deliver those images. I had hopes that CUDA will save my @ss as we all know that GPU is great for studio/product shots. Well, that wouldn't render with CUDA too. My PC just locks up and I have to restart it. This simple material proves to be a real problem for my PC and Vray.

[vlado]

It really depends on the material. If you can get me a scene, I can probably give you some tips on optimizing it.

From your images, it looks like there's a lot more light scattering going on in the V-Ray image than in the Corona one, which generally looks darker - that explains why it also renders faster.

Best regards,
Vlado

[Alex_M]

Here's the scene for anyone that wants to take a shot at it: https://we.tl/FyMCihaW14

Are there ways to fake this type of material even if it doesn't look that realistic?

[Ihno]

Seems to be much faster here... I've a 5950x so my system is a bit faster than yours but it cleaned the image in about 5 min. Shouldn't be so much faster I think. Just opened the scene and pushed render.
Tried to reboot?
Edit: Just realized you set the rendertime to 5 min's
Takes quite a bit longer to reach the noise threshold

[Alex_M]

Thanks Ihno, actually it does render fine in 5 min now! What happened? Something must have happened yesterday that messed with my PC. Thank god it's fine now!

PS: Here's the render at 1024 x 768 rendered on 2 x 4930k + 2 x 2600k. Took 6-7 min. I'm finally happy with the result and render times. Before it wouldn't even go past pass 0 after 10 minutes.