Subsurface Opacity value not working?

[Nintenjo (NintenjoWii)]

I want to add subsurface to my material so that light is scattered through the objects, i understand the way to control the amount of scattered light on an object is to use the Opacity… 0 means all the light will pass through, and 1 no light will pass through… I was using a texture to control that variable and was not seeing the expected results, so instead, i tried a very basic setup using only a float to control Opacity…

From my test it does nothing… here is a simple scene with the sun behind a sphere and flattened cube, and even with 0 or 1 set on the opacity, the result is the same.

But what I would expect to see is something close to this result from Arnold…

Any idea what could be wrong? (I’m using Unreal 5.1).

[dblzeero]

Try using a subsurface profile. I messed around with it a while ago. I opened up the file I tested when I saw this post.

[Nintenjo (NintenjoWii)]

Not sure this would help… but i can try. I have just done a fresh install of 5.2.1 created the exact same material in an empty scene, and its working exactly as i would have expected…

With opacity controlling the radius as I would have hoped.

So now I’m thinking is something in my project stopping it from working or is it a bug in 5.1 ?? (but that seems unlikely as it’s such a basic feature of materials in unreal).

[Nintenjo (NintenjoWii)]

Arrgghh this is a nightmare, i loaded my project into 5.2 and it does not work, so somthing in my project setup is causing it to stop working, this is very annoying as i have no idea what settings might cause that.

[Nintenjo (NintenjoWii)]

For future reference if anyone else has this issue… I have resolved it but not entirely sure how, but here is what I did:

• Copy Rendering Project settings from working 5.2 to 5.1 (didnt help)
• Copy material from 5.2 working versions (didnt help)
• Copy Sun Settings from 5.2 working version (didnt help)
• Tried to migrate level from 5.2 to 5.1 (this cant be done as levels are not backward compatible)
• Upgraded my project to 5.2 (didnt help)
• Copy level from working 5.2 version to new Upgraded project in 5.2 - This worked.

I can only think a setting in my original 5.1 level was causing it to not work, it could be a combination of the Sun Light settings, but also the Exposure control. As my original scene had a much lower Candels value for the sun vs the new scene in 5.2 which was about 75k lux… Im not sure why this would cause and issue but perhaps my original scene had such a low value of light being emitted by the Sun the subsurface was just super faint and failing to calculate correctly.

Not much help I know, but I’ve spent nearly 2 days on this and need to carry on.