Help on Camera DOF

[Byteman3D]

I have a camera, targeted and focused onto a glass marble.
When I turn on DOF and set some parameters, my glass marble is focused and sharp, while the background and foreground are blurred.
I need to make the scene behind the marble blurred but the marble and the scene in front of the marble sharp and focused.

Near will be in focus with the marble and the back will be blurred. Any help on this?

[Designerman77]

Sounds like you have a big aperture (small F-stop like 4 or 2) and your object in focus.

Then the effect you describe is absolutely normal. Background and everything in front of your focussed object will be blurry, except your object - depending on distances.

[Juraj]

Very simple, focus in front of the subject :- ). In CGI there is no physical limitation of minimum focus distance, you can even set it 1 cm  in front of camera (Super Macro!).

So focus reasonably closer to you than your subject. Then adjust DOF until subject is sharp. Do this using the viewport helping planes that show you the "zone".

Fun fact: In theory it is possible to program for CGI a fully individually adjustable focus planes. I've seen Vlado mention it many years ago, but said it would create some issues. There is probably some post-production plugin that does it much easily.

[Byteman3D]

I'm not unfamiliar with F-stops and sorts of photography parameters however, my camera is 330cm away from the subject and the background wall is 100cm away from the subject.
I need is some sort of fake DOF setup. The subject and front of it should be in focus while the background (at 1 m dist. from the subject) will be blurred. The floor has an image on it and it should also reflect the changing focus. I guess I'm trying to achieve something physically impossible.
Sample image is nice but the subject is in focus while both the front and back is out of focus.

[romullus]

As Juraj already said, you need to create physical camera and enable DOF in its settings. That way, you'll get visual representation of focus zone and will be able to adjust it to your needs in no time. Enable DOF, then adjust aperture and/or target distance

[Designerman77]

I'm not unfamiliar with F-stops and sorts of photography parameters however, my camera is 330cm away from the subject and the background wall is 100cm away from the subject.
I need is some sort of fake DOF setup. The subject and front of it should be in focus while the background (at 1 m dist. from the subject) will be blurred. The floor has an image on it and it should also reflect the changing focus. I guess I'm trying to achieve something physically impossible.
Sample image is nice but the subject is in focus while both the front and back is out of focus.

Render two or three pictures and combine them in PS.

[Juraj]

You don't even need to render it multiple times if you are ok with Z-Depth based post-production DOF ( no refraction,etc... ).

But otherwise that's the most flexible workflow indeed. Combine tack-sharp and shallow DOF renderings using Z-depth as the mask Photoshop. Allows every unrealistic combination possible.