Transparency problem

[Tgjohnson]

I imagine it can be done with creative use of track mattes and duplciated layers.

[Darby Edelen]

If I understand you correctly you’re trying to have a layer that is farther back in Z-space show up as though it is on top of a layer that is closer to the camera. This can be accomplished by putting the layer that is closer (“Front”) beneath the farther layer (“Back”) in the timeline then setting the “Front” layer to use “Back” as a Track Matte.

Make sure you use an ‘Alpha Inverted’ Track Matte so that the areas of the “Back” layer that are non-transparent cause the “Front” layer to become transparent (sorry if this is confusing, search in the After Effects help files for ‘Track Matte’). The last step would be to make the “Back” layer visible again (when you set a Track Matte AE automatically toggles the Track Matte layer’s visibility off).

[Alberto Forlai]

Thank you, I feel that this is not so simple, I’ll try it and I’ll post a answer.

Alberto

[Alberto Forlai]

Well, I have done some experiment but I have not solved the problem.
To explain better what I want to do I have put here an image of my work.
I want to simulate a camera diaphragm, using 8 levels (blades)
Each blade is locked on an corner and rotate on it.
In the image that follow you can see the result

Blade number 1 is the topmost, blade number 8 is the lower.
For a correct simulation blade 1 must be on the top but must also go under blade 8 and also under blade 7
Of course when the diaphragm close the number of blades that must go on Blade 1 increase see the image below:

The result shoud have to be :

I have no idea how to simulate this.

Thanks for any advice.

Alberto