Use F-stop issue in 28.1x Tweet

[J.C]

When Use-F-stop is enabled in Octane camera settings the render preview and final render has different levels of lens blur. Preview has less while final render has more blur.
When Use F-stop is disabled and aperture slider is used both render views are the same.

[linograndiotoy]

I can't reproduce the issue on a scene I made.
Can you please share a very simple scene showing it? Thanks.

[J.C]

Here is the file with the issue.

[J.C]

Still not fixed in 28.13

[linograndiotoy]

From the developer:

"This "f-stop" difference is a limitation.

Why the "f-stop" produces different blur effect?
Basically, in Octane, the final "dof" blur effect is determined by the "Aperture" value. So the preview and final render produce the same results when using the "Aperture".
When the "f-stop" is used, Octane calculates the "Aperture" based on the focal length and f-stop. The f-stop is exactly the same. But the focal length has to be modified between preview and final render, which results in a different "Aperture" and "dof" blur effect.

Why the focal length has to be changed?
Briefly, it's caused by the change of the FOV. In Octane, the focal length and FOV are synced. When we change the FOV, the focal length is changed too.
And the FOV is different between preview and final render as the resolution is different. The preview resolution is determined by the viewport while the final render is determined by the "Resolution" property.
So the focal length in Octane is different in Octane. All of those leads to a different "Aperture" and blur effect.


I can implement a f-stop to aperture converter in the code. No matter whether users enable "use f-stop", we will convert them to "aperture" in all cases. (it seems to be how Cycles does it).
But this way breaks backward compatibility. So I can provide a new option for users to decide whether they want to use the new mode."

We'll go for the new option.

[J.C]

Thanks for the information!