zDepth Renderelement in animation: How to get the focus point at a grey mid value, to add Defocus only in compositing?

[BeneZ]

Hello,
I'm testing zDepth in an animation sequence.
I have already animated the focus distance with a locator (from camera and also from the renderelement zdepth), so the focus distance is correctly specified.
But I get a much too dark result.

I already read, that near and far clip plane influences this, but changing these settings or toggling "Auto render clip plane" doesn't change anything.

When I use zDepth RE without specified "Camera ZDepth" it renders fine, but this does not use my focal point distance at all.
So have I to animate Depth black and Depth White instead? And if so, which sense makesthe Camera ZDepth value?

I would expect, that in a sequence my specified focus point renders always as medium grey, and depth black & depth white were following in "same distance" from that specified focus.

I want to render sharp, but to add zdeth blurriness in compositing.

How can I achieve this?

Thanks

[SonyBoy]

I think I understand what you're asking, which is how to keep your focus distance in 3D rendering to the Z channel as a consistent mid gray? I'm not really sure how to do that, since I believe the 50 precent gray point is going to be dictated by your near and far points in the depth render element as calculated from the camera, not from your point of focus. But why are you trying to do this? The whole point of doing depth blurring in post is that you are able to fully control what's in focus and what isn't outside of the 3D environment. So relative gray values are pretty arbitrary as you can dial your depth of field and up and down to taste in post. It is possible to sometimes not always get the range of values you want in a depth pass, particularly if you have a shot that includes both extreme close ups and long shots in a single camera move. In those cases it might be necessary to animate near and far points in 3D, or use animated color correction in post to compress depth values. But those are unusual situations. And if you render your depth pass to 32-bit, you should have more than enough values in there for control. If you really need to do what you describe you might be able to do it by using a black to white ramp parented to your focus distance locator, projected sideways into your scene -- or something along those lines. Hard to say without a clearer understanding of your scene.

[BeneZ]

Yes, I have a scene with quick camera and focus changes and I spent a while to keep the focus point perfect with a locator through the entire sequence.
But now I don't now, how not make a use of it in render passes for compositing (when rendering a sharp image and applying defocus later in nuke e.g.).

I guess, the only way to keep that focus point is, when a "middle grey" is assigned in the depth render pass.

I guess there must be here some people, who know that task?
Thanks

[SonyBoy]

You still seem to be suggesting that there is an intrinsic point of focus in a depth pass, but there isn't and in fact that's one of the reasons for doing depth blurring in post -- you can set your in focus range to taste and change it without having to re-render from 3D as you would if you used in-camera depth of field. So your mid gray point, in that context at least, is meaningless. You can just as easily set any other grayscale value to be in focus. If you need to animate the focus depth, you'd do this either by animating values on the depth blurring effect (in Nuke most likely a zDefocus node, in After Effects perhaps Frischluft Lenscare), or by animating color correction on the depth pass to push the black to white range, or both.